Patent Publication Number: US-9414888-B2

Title: Devices and methods for radiation-based dermatological treatments

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-In-Part of U.S. patent application Ser. No. 13/366,202 filed on Feb. 3, 2012, which claims priority from U.S. Provisional Application No. 61/439,353 filed on Feb. 3, 2011; U.S. Provisional Application No. 61/444,079 filed on Feb. 17, 2011; U.S. Provisional Application No. 61/469,316 filed on Mar. 30, 2011; U.S. Provisional Application No. 61/533,641 filed on Sep. 12, 2011; U.S. Provisional Application No. 61/533,677 filed on Sep. 12, 2011; U.S. Provisional Application No. 61/533,786 filed on Sep. 12, 2011; U.S. Provisional Application No. 61/545,481 filed on Oct. 10, 2011; U.S. Provisional Application No. 61/563,491 filed on Nov. 23, 2011 and U.S. Provisional Application No. 61/594,128 filed on Feb. 2, 2012, all of which applications are hereby incorporated by reference in their entirety. 
     This application also claims priority from U.S. Provisional Application No. 61/613,778 filed on Mar. 21, 2012, which application is hereby incorporated by reference in its entirety. 
     This application is also related to Co-Pending U.S. patent application Ser. No. 13/443,717 filed on Apr. 10, 2012; Co-Pending U.S. patent application Ser. No. 13/443,788 filed on Apr. 10, 2012; Co-Pending U.S. patent application Ser. No. 13/443,808 filed on Apr. 10, 2012; Co-Pending U.S. patent application Ser. No. 13/443,876 filed on Apr. 10, 2012; Co-Pending U.S. patent application Ser. No. 13/443,863 filed on Apr. 10, 2012, Co-Pending U.S. patent application Ser. No. 13/443,880 filed on Apr. 10, 2012; and Co-Pending U.S. patent application Ser. No. 13/443,821 filed on Apr. 10, 2012, all of which co-pending applications are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure is related to radiation-based dermatological treatment devices and methods, e.g., laser-based devices for providing fractional treatment, or devices using any other type of radiation source for providing any other suitable type of dermatological treatment. Some embodiments include an automated scanning system for scanning a beam to multiple locations on the skin. 
     BACKGROUND 
     Light-based treatment of tissue is used for a variety of applications, such as hair removal, skin rejuvenation, wrinkle treatment, acne treatment, treatment of vascular lesions (e.g., spider veins, diffuse redness, etc.), treatment of cellulite, treatment of pigmented legions (e.g., age spots, sun spots, moles, etc.), tattoo removal, and various other treatments. Such treatments generally include delivering light or laser radiation to an area of tissue on a person&#39;s body, e.g., the skin or internal tissue, to treat the tissue in a photochemical, photobiological, thermal, or other manner, which can be ablative or non-ablative, among other properties, depending on the particular application. 
     Light-based treatment devices include various types of radiation sources, such as lasers, LEDs, flashlamps, etc. For example, laser diodes are particularly suitable for certain light-based treatments and devices for providing such treatments. Laser diodes are compact, as they are typically built on one chip that contains the major necessary components for light generation other than a power source. Further, laser diodes typically provide an efficiency of up to 50% or higher, which enables them to be driven by low electrical power compared to certain other lasers. Laser diodes allow direct excitation with small electric currents, such that conventional transistor based circuits can be used to power the laser. 
     Other characteristics typical of laser diodes include high temperature sensitivity/tunability, and a highly divergent beam compared to certain other lasers. Laser diodes typically emit a beam having an axis-asymmetric profile in a plane transverse to the optical axis of the laser. In particular, the emitted beam diverges significantly faster in a first axis (referred to as the “fast axis”) than in an orthogonal second axis (referred to as the “slow axis”). In contrast, other types of lasers, e.g., fiber lasers, typically emit a beam having an axis-symmetric profile in the transverse plane. 
     Laser-based treatment devices typically include optics downstream of the laser source to scan, shape, condition, direct, and/or otherwise influence the laser radiation to the target tissue as desired. Such optics may include lenses, mirrors, and other reflective and/or transmissive elements, for controlling optical parameters of the beam, such as the direction, propagation properties or shape (e.g., convergent, divergent, collimated), spot size, angular distribution, temporal and spatial coherence, and/or intensity profile of the beam, for example. Some devices include systems for scanning a laser beam in order to create a pattern of radiated areas (e.g., spots, lines, or other shapes) in the tissue. For some applications, the scanned pattern of radiated areas overlap each other, or substantially abut each other, or are continuous, in order to provide complete coverage of a target area of tissue. For other applications, e.g., certain wrinkle treatments, vascular treatments, pigmentation treatments, anti-inflammatory treatments, and other skin rejuvenation treatments, the scanned radiated areas may be spaced apart from each other by non-irradiated areas such that only a fraction of the overall target area of the tissue is radiated during a treatment session. Thus, in such applications, there are generally regions of untreated tissue between regions of treated tissue. This type of treatment is known as “fractional” treatment (or more specifically, fractional photothermolysis in some cases) because only a fraction of the target area is irradiated during a treatment session. 
     Some known scanning systems move the radiation source itself relative to the device housing or structure in order to form the scanned pattern of radiated areas. Other known scanning systems utilize one or more moving optical elements (e.g., mirrors and/or lenses) in order to scan a radiation beam into a pattern of radiated areas, rather than moving the radiation source relative to the device housing or structure. 
     SUMMARY 
     The present disclosure is related to radiation-based dermatological treatment devices and methods, e.g., laser-based devices for providing fractional treatment. 
     In some embodiments, a hand-held compact device is provided for providing radiation-based dermatological treatments, e.g., skin resurfacing, skin rejuvenation, wrinkle treatment, removal or reduction of pigmentation, hair removal, acne treatment, skin tightening, redness, vascular treatments such as telangectasia or port-wine stains, stretch marks, anti-aging, or anti-inflammatory skin treatments such as treating rosacea, acne, or vitiligo. Other embodiments may apply to non-skin tissue treatment, such as eye tissue or internal organs. In particular embodiments, the device includes one or more radiation sources (e.g., one or more lasers) and an automated scanning system for delivering an array of scanned beams to the skin, while the device is manually moved across the skin, to produce an array of discrete treatment spots on the skin, e.g., to provide a fractional thermal treatment. In other embodiments, the device may be configured for full coverage of a treatment area (i.e., non-fractional treatment), e.g., for skin tightening. In some embodiments, the device may provide a non-thermal treatment, e.g., a photochemical treatment such as a blue light treatment that acts on bacterial porphyrins, photobiological treatment such as low-level light therapy that acts on mitochondria, photodynamic therapy (PDT), etc. 
     The device may include one or more radiation sources that radiate energy in the form of one or more beams to produce one or more irradiated areas on the skin that provide a dermatological treatment. As used herein, “radiation” may include any radiative energy, including electromagnetic radiation, UV, visible, and IP light, radio frequency, ultrasound, microwave, etc. A radiation source may include any suitable device for radiating one or more coherent or incoherent energy beams, e.g., a laser, LED, flashlamp, ultrasound device, RF device, microwave emitter, etc. Energy beams may be generated in any suitable manner, such as pulsed, continuous wave (CW), or otherwise (depending on the particular embodiment, application, or device setting), and then scanned by an automated scanning system to deliver a scanned array of output beams to the skin. In some embodiments, the radiation source is a laser, e.g., an edge emitting laser diode, laser diode bar, HeNe laser, YAG laser, VCSEL laser, or other types of laser, that generates one or more laser beams that are scanned and delivered to the skin to effect a treatment. It should be understood that references herein to a radiation source or an energy beam in the singular should be interpreted to mean at least one radiation source or at least one energy beam, unless otherwise specified, e.g., references to a single radiation source or a single energy beam, or references to radiation sources or energy beams (or references to multiple radiation sources or multiple energy beams). 
     In some embodiments, the device provides automatically scanned and/or pulsed energy beams to the skin to provide a fractional dermatological treatment, e.g., skin resurfacing, skin rejuvenation, wrinkle treatment, removal or reduction of pigmentation, treatment of coarse skin caused by photodamage, etc. Each scanned and/or pulsed energy beam delivered to the skin is referred to herein as a “delivered beam.” In embodiments that provide a fractional treatment, each delivered beam forms an irradiated treatment spot (or “treatment spot”) on the surface of the skin, and a three-dimensional volume of thermally damaged (or otherwise influenced, such as photochemically) skin extending below the surface of the skin, referred to herein as a micro thermal zone (MTZ). Each MTZ may extend from the skin surface downward into the skin, or may begin at some depth below the skin surface and extend further downward into the skin, depending on the embodiment, device settings, or particular application. The device may be configured to generate an array of MTZs in the skin that are laterally spaced apart from each other by volumes of untreated (i.e., non-irradiated or less irradiated) skin. For example, an application end of the device may be manually moved (e.g., in a gliding manner) across the surface of the skin during a treatment session. An automatically scanned array of beams may be delivered to the skin (to generate an array of MTZs in the skin) during the movement of the device across the skin, which is referred to herein as a “gliding mode” treatment, or between movements of the device across the skin, which is referred to herein as a “stamping mode” treatment, or a combination of these modes, or a different mode of operation. The skin&#39;s healing response, promoted by the areas of untreated (i.e., non-irradiated) skin between adjacent MTZs, provides fractional treatment benefits in the treatment area (e.g., skin resurfacing or rejuvenation, wrinkle removal or reduction, pigment removal or reduction, etc.). In some embodiments or applications, the compact, hand-held device may yield results similar to professional devices, but leverages a home use model to more gradually deliver the equivalent of a single professional dose over multiple treatments or days (e.g., a 30 day treatment routine or a two treatment sessions per week treatment routine) Skin rejuvenation generally includes at least one or more of treatments for wrinkles, dyschromia, pigmented lesions, actinic kerotosis, melasma, skin texture, redness or erythema, skin tightening, skin laxity, and other treatments. 
     As used herein, “fractional” treatment means treatment in which individual treatment spots generated on the skin surface are physically separated from each other by areas of non-irradiated (or less irradiated) skin (such that the MTZs corresponding to such treatment spots are generally physically separated from each other). In other words, in a fractional treatment, adjacent treatment spots (and thus their corresponding MTZs) do not touch or overlap each other. In some embodiments in which a radiation source (e.g., laser) is automatically scanned and/or pulsed to generate a successive array of treatment spots on the skin, the automated scan rate and/or the pulse rate may be set and/or controlled based on various factors, such as a typical or expected speed at which the device is manually moved or glided across the skin, referred to herein as the “manual glide speed” (e.g., in a gliding mode operation of the device). In particular, the automated scan rate and/or the pulse rate may be set and/or controlled such that for a range of typical or expected manual (or mechanically-driven) glide speeds, adjacent treatment spots or adjacent rows of treatment spots are generally physically separated from each other by areas of non-treated skin (i.e., fractional treatment is provided). In some embodiments, the device delivers a successive series of automatically scanned rows of beams to the skin while the device is manually glided across the skin, to produce successive rows of treatment spots on the skin. In such embodiments, the automated scan rate may be set or selected such that for a range of typical or expected manual glide speeds, adjacent rows of treatment spots are physically separated from each other from a predetermined minimum non-zero distance, e.g., 1500 μm. 
     In some embodiments, the device may be configured to provide 3D fractional treatment, by generating MTZs at various depths in the skin. For example, this may be achieved (a) by scanning beams to generate MTZs at different depths, e.g., using scanning optics configured to provide different focal depths, or by controlling wavelengths, pulse energies, pulse durations, etc. for different scanned beams, (b) by dynamically moving or adjusting one or more radiation sources, scanning optics or other optics, e.g., to dynamically adjust the focal points of the delivered beams, (c) by providing multiple radiation sources configured to generate MTZs at different depths, e.g., by using multiple radiation sources arranged at different distances from the skin surface, focal depths, wavelengths, pulse energies, pulse durations, or other parameters, or (d) in any other suitable manner. 
     The device may include any suitable beam scanning system including any suitable (transmissive, reflective, or otherwise) beam scanning optics. In some embodiments, the device may include a transmissive disk-shaped multi-sector beam scanning element including multiple sectors (e.g., lenslets) arranged circumferentially around the scanning element. The multiple sectors or lenslets of the disk-shaped scanning element may be configured to that scan an input beam into a sequential array of output beams, each being angularly and/or translationally offset from at least one other output beam, to provide an array of treatment spots at different locations on the skin. 
     In other embodiments, the device may include a transmissive cup-shaped multi-sector beam scanning element including multiple sectors (e.g., lenslets) arranged circumferentially around the scanning element. The multiple sectors or lenslets of the cup-shaped scanning element may be configured to that scan an input beam into a sequential array of output beams, each being angularly and/or translationally offset from at least one other output beam, to provide an array of treatment spots at different locations on the skin. 
     In other embodiments, the device may include a reflective stair-stepped beam scanning element including multiple sectors (e.g., reflective surfaces) arranged circumferentially around the scanning element. The multiple sectors or reflective surfaces of the stair-stepped scanning element may be configured to that scan an input beam into a sequential array of output beams, each being angularly and/or translationally offset from at least one other output beam, to provide an array of treatment spots at different locations on the skin. 
     In any of these embodiments, the beam scanning element may be configured to provide “constant angular deflection” output beams, wherein each output beam from the scanning element maintains a constant or substantially constant angle of deflection with respect to the device housing (i.e., a constant propagation direction) for the duration of that output beam (i.e., for the duration that the input beam acts on the scanning element sector that produces that output beam). In other words, with constant angular deflection output beams, if the device is held stationary on the skin, each output beam creates a stationary or substantially stationary treatment spot on the skin. 
     In some embodiments, the device includes a displacement-based control system including a displacement sensor and electronics configured to measure or estimate the lateral displacement of the device across the skin and control one or more aspect of the device (e.g., on/off status of the radiation source, pulse rate, automated scan rate, etc.) based on the determined displacement of the device. For example, the displacement-based control system may control the delivery of scanned beams to provide a desired spacing between scanned rows of treatment spots (for a fractional treatment) and/or to prevent or reduce the incidence or likelihood of treatment spot overlap. For example, as the device generates and delivers a series of scanned beam rows to create a series of treatment spot rows, the displacement monitoring and control system may allow the next scanned beam row (or individual beams within the row) to be generated and/or delivered only if the device has been displaced a predetermined distance from a previous treatment location (e.g., the device location at the beginning of the previously delivered scanned beam row). Otherwise, the device may interrupt the generation and/or delivery of beams until the displacement of the device meets or exceeds the predetermined distance. In some embodiments, the predetermined distance is based on a predetermined number of consecutive surface features in the skin that may be detected by a displacement sensor. In other embodiments, the displacement may be measured with other types of distance detection such as mechanical rollers, optical mouse sensors, etc. In other embodiments, a dwell sensor and/or a motion sensor may be used to reduce the risk of repeatedly treating the same skin region. 
     In some embodiments, the device includes a single radiation source, e.g., an edge emitting laser diode, a VCSEL having a single micro-emitter zone, an LED, or a flashlamp. For certain treatments, the single radiation source may be automatically scanned to provide a line or array of delivered beams extending generally in a “scan direction,” while the device is glided across the skin in a “glide direction” generally perpendicular to the scan direction, thus form a generally two-dimensional array of treatment spots on the skin. A larger array of treatment spots can thus be created by gliding the device across the skin multiple times in any suitable direction(s) or pattern(s). 
     In other embodiments, the device includes multiple radiation sources, e.g., multiple edge emitting laser diodes, an laser diode bar having multiple emitters (or multiple laser diode bars), a VCSEL having multiple micro-emitter zones (or multiple VCSELs), or multiple LEDs. The multiple radiation sources may be collectively scanned by an automated scanning system or separately scanned by multiple automated scanning systems, to form an array of delivered beams to the skin as desired. 
     In some embodiments, the device is fully or substantially self-contained in a compact, hand-held housing. For example, in some battery-powered embodiments of the device, the radiation source(s), user interface(s), control electronics, sensor(s), battery or batteries, fan(s) or other cooling system (if any), scanning system, and/or any other optics, are all contained in a compact, hand-held housing. Similarly, in some wall-outlet-powered embodiments of the device, the radiation source(s), user interface(s), control electronics, sensor(s), battery or batteries, fan(s) or other cooling system (if any), scanning system, and/or any other optics, are all contained in a compact, hand-held housing, with only the power cord extending from the device. 
     In other embodiments, one or more main components of the device may be separate from the device housing, and connected by any suitable physical or wireless means (e.g., wire, cable, fiber, wireless communications link, etc.) 
     In some embodiments, the device provides eye safe radiation, e.g., by delivering a substantially divergent energy beam (e.g., using an edge emitting laser diode with no downstream optics), and/or using an eye safety control system including one or more sensors, and/or by any other suitable manner. In some laser-based embodiments or settings, the device meets the Class 1M or better (such as Class 1) eye safety classification per the IEC 60825-1, referred to herein as “Level 1 eye safety” for convenience. In other embodiments or settings, the device exceeds the relevant Maximum Permissible Exposure (MPE) (for 700-1050 nm wavelength radiation) or Accessible Emission Limit (AEL) (for 1400-1500 nm or 1800-2600 nm wavelength radiation) by less than 50%, referred to herein as “Level 2 eye safety” for convenience. In still other embodiments or settings, the device exceeds the relevant MPE (for 700-1050 nm wavelength radiation) or AEL (for 1400-1500 nm or 1800-2600 nm wavelength radiation) by less than 100%, referred to herein as “Level 3 eye safety” for convenience. The Accessible Emission Limit (AEL), as specified in IEC 60825-1, e.g., for 700-1050 nm wavelength radiation, is discussed below. Maximum Permissible Exposure (MPE), which is relevant, e.g., for 700-1050 nm wavelength radiation, is not discussed below but is specified in IEC 60825-1:2007. In other embodiments or settings, the device meets the next highest eye safety classification after Class 1M per the IEC 60825-1, i.e., Class 3B, referred to herein as “Level 4 eye safety” for convenience. 
     In some embodiments, the device may be suitable for providing a fractional treatment using a home-use treatment plan that includes treatment sessions of a few minutes or less, once or twice a day. In some embodiments, a treatment session of 4 minutes, for example, may allow an effective treatment of about 300 cm 2  (about 4 in 2 ), e.g., for a full-face treatment. Further, certain embodiments permits the use a small battery, and allow for thermal control without any fan(s). For example, in some embodiments, a small cylindrical block of copper can absorb the waste heat from a laser during a treatment session, preventing excessive temperature rise of the diode without the use of a fan. Other embodiments may include at least one fan for increased cooling of the device components. 
     In some embodiments, the device may deliver a predetermined number of beams (thus providing a predetermined number of treatment spots on the skin), which may correspond to a selected treatment area (e.g., full face, periorbital area, etc.), operational mode, energy level, power level, and/or other treatment parameters. In some embodiments, the device may be glided at any speed across the skin within the target area, and repeatedly glided over the target area multiple times until the predetermined number of beams have been delivered, at which point the device may automatically terminate the treatment. 
     In some embodiments, the device may be controlled to prevent, limit, or reduce the incidence or likelihood of treatment spot overlap, excessive treatment spot density, or other non-desirable treatment conditions, e.g., based on feedback from one or more sensors (e.g., one or more dwell sensors, motion/speed sensors, and/or displacement sensors). For example, the device may monitor the speed or displacement of the device relative to the skin and control the radiation source accordingly, e.g., by turning off the radiation source, reducing the pulse rate, etc. upon detecting that the device has not been displaced on the skin a minimum threshold distance from a prior treatment location. Further, in some embodiments, the pulse rate may be automatically adjustable by the device and/or manually adjustable by the user, e.g., to accommodate different manual glide speeds and/or different comfort levels or pain tolerance levels of the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the disclosure may be understood by referring, in part, to the following description and the accompanying drawings wherein: 
         FIG. 1  illustrates components of an example radiation-based treatment device configured to deliver scanned beams to a user (e.g., to the user&#39;s skin), according to certain embodiments. 
         FIG. 2  illustrates an example control system for the radiation-based treatment device of  FIG. 1 , according to example embodiments. 
         FIGS. 3A-3D  illustrate representations of optical systems  15  for a scanned-beam radiation-based treatment device, according to example embodiments. 
         FIG. 4  illustrates a schematic layout of various components of a scanned-beam radiation-based treatment device, according to example embodiments. 
         FIGS. 5A and 5B  illustrate the general concept of creating rows of treatment spots on the skin using a scanned-beam radiation-based treatment device, according to example embodiments. 
         FIG. 6A  illustrates a basic structure of an example rotating element for scanning an input beam to form an array of output beams, according to certain embodiments. 
         FIGS. 6B and 6C  illustrate example patterns treatment spots created by the beam-scanning element of  FIG. 6A , according to certain embodiments. 
         FIGS. 7A-7C  illustrate an example disk-shaped rotating beam-scanning element, according to certain embodiments. 
         FIGS. 8A-8E  illustrate an example cup-shaped rotating beam-scanning element, according to certain embodiments. 
         FIGS. 9A and 9B  illustrate optical aspects of the example beam-scanning elements of  FIGS. 7A-7C  and  FIGS. 8A-8E , according to certain embodiments. 
         FIGS. 10A and 10B  illustrate top and side views, respectively, of a beam generation and delivery system that includes a disk-shaped rotating scanning element, according to certain embodiments. 
         FIGS. 11A and 11B  illustrate top and side views, respectively, of a beam generation and delivery system that includes a cup-shaped rotating scanning element, according to certain embodiments. 
         FIG. 12  illustrates an example stair-stepped rotating scanning element, according to an example embodiment. 
         FIGS. 13 and 14  illustrate the basic operation of a stair-stepped rotating scanning element, according to an certain embodiments. 
         FIG. 15A-15C  illustrate example downstream optics for use with a stair-stepped rotating scanning element, according to an certain embodiments. 
         FIG. 16  illustrate example downstream optics for correcting the path length of different scanned beams in a system including a stair-stepped rotating scanning element, according to an certain embodiments. 
         FIGS. 17A-17B  illustrate three-dimensional and end views, respectively, of an example stair-stepped rotating scanning element, according to an example embodiment. 
         FIGS. 18A-18B  illustrate example path length correcting optics for use with the stair-stepped rotating scanning element of  FIGS. 17A-17B , according to an example embodiment. 
         FIGS. 19 and 20  illustrate two example optical systems that include a stair-stepped rotating scanning element for scanning an input beam to create a scanned array of treatment spots on the skin, according to certain embodiments. 
         FIG. 21A-21C  illustrates a first example arrangement of sectors of a rotating beam scanning element ( FIG. 21A ), and resulting patterns of treatment spots created by such arrangement ( FIGS. 21B and 21C ), according to example embodiments. 
         FIG. 22A-22C  illustrates a second example arrangement of sectors of a rotating beam scanning element ( FIG. 22A ), and resulting patterns of treatment spots created by such arrangement ( FIGS. 22B and 22C ), according to example embodiments. 
         FIGS. 23A-23B, 24A-24B, and 25A-25B  illustrates example patterns of treatment spots created by various configurations of a rotating beam scanning element, according to example embodiments. 
         FIGS. 26A and 26B  illustrate the smearing of treatment spots created by “constant angular deflection” beams, due to movement of the device during the delivery of the beams, according to certain embodiments. 
         FIGS. 27A and 27B  illustrate the smearing and/or shifting of treatment spots created by “shifting deflection” beams, according to certain embodiments. 
         FIGS. 28A-28F  illustrate the various radiation modes with respect to an example disc-shaped or cup-shaped rotating element having four deflection sectors, according to certain embodiments. 
         FIGS. 29A-29F  illustrate the same various radiation modes with respect to an example stair-stepped type rotating element having four deflection sectors, according to certain embodiments. 
         FIG. 30  illustrates an example scanning element having reflection sectors of different sizes, according to certain embodiments. 
         FIG. 31  illustrates an example rotating scanning element having four deflection sectors separated by non-propagating areas, according to an example embodiment. 
         FIGS. 32A-32C  illustrate beam intensity profiles in the slow and fast axis for on-axis scanned beams ( FIG. 32A ) and off-axis scanned beams ( FIG. 32B ), as well as a graph illustrating the fraction of “ensquared energy” as a function of the target area, for scanned-beam treatment devices according to certain embodiments. 
         FIGS. 33A and 33B  illustrate a first example embodiment of a radiation engine for use in a radiation-beam treatment device, according to certain embodiments. 
         FIG. 34  illustrates a second example embodiment of a radiation engine for use in a radiation-beam treatment device, according to certain embodiments. 
         FIGS. 35A and 35B  illustrate a third example embodiment of a radiation engine for use in a radiation-beam treatment device, according to certain embodiments. 
         FIGS. 36A-36C  illustrate a first example laser package for use in a radiation-beam treatment device, according to certain embodiments. 
         FIG. 37  illustrates a second example laser package for use in a radiation-beam treatment device, according to certain embodiments. 
         FIG. 38  illustrates a block diagram of an example displacement-based control system for a scanned-beam treatment device, according to certain embodiments. 
         FIG. 39  illustrates a flowchart of an example method for controlling a device using a displacement-based control system, while the device is used either in a gliding mode or a stamping mode, according to certain embodiments. 
         FIG. 40A  illustrates a first example single-pixel displacement sensor for use in a displacement-based control system, according to certain embodiments. 
         FIG. 40B  illustrates a second example single-pixel displacement sensor for use in a displacement-based control system, according to certain embodiments. 
         FIG. 40C  illustrates a third example single-pixel displacement sensor for use in a displacement-based control system, according to certain embodiments. 
         FIG. 41  illustrates a pair of experimental data plots for an embodiment of an optical displacement sensor being scanned above the skin surface of a human hand. 
         FIG. 42  represents an example plot of a signal generated by a detector as a displacement sensor is moved across the skin of a human hand. 
         FIG. 43  illustrates three data plots: a raw signal plot, filtered signal plot, and a intrinsic skin feature detection plot, for detecting skin features based on signals from a displacement sensor, according to certain embodiments. 
         FIG. 44  illustrates a more specific example of the general method of  FIG. 39  for controlling a device using a displacement-based control system, according to certain embodiments. 
         FIG. 45  illustrates an example multi-pixel imaging correlation sensor, of the type used in optical mice for computer input, for detecting displacement along the skin, according to certain embodiments. 
         FIG. 46  illustrates an example method for controlling a device using a displacement-based control system that employs a multi-pixel displacement sensor, while the device is used either in a gliding mode or a stamping mode, according to certain embodiments. 
         FIG. 47  illustrates an example method for executing a treatment session for providing treatment (e.g., fractional light treatment) to a user in certain embodiments and/or settings of the device. 
         FIGS. 48A-48G  illustrate example embodiments of a roller-based sensor that may be used a displacement sensor, or a motion/speed sensor, or both, for use in certain embodiments. 
         FIG. 49  illustrates an example method for providing “usability” control of radiation delivery based on feedback from contact sensors and displacement sensors, according to an example embodiment. 
         FIG. 50  illustrates an example configuration of the application end of a scanned-beam treatment device, indicating an arrangement of contact sensors and displacement sensors, according to an example embodiment. 
         FIGS. 51A-51D  illustrate an example optical eye safety sensor ( FIGS. 51A and 51B ) according to certain embodiments, as well as representation of local surface normal directions for example corneas of different shapes ( FIGS. 51C and 51D ). 
         FIG. 52  illustrates an example multi-sensor control/safety system that includes one or more eye safety sensors and one or more skin contact sensors arranged on or near the application end of the device, according to certain embodiments. 
         FIG. 53  illustrates an example method for controlling a device using a multi-sensor control/safety system, according to certain embodiments. 
         FIG. 54  illustrates an example method for calibrating an eye safety sensor for one or multiple users, according to certain embodiments. 
         FIG. 55  illustrates an example system for controlling a scanning system motor and laser pulse parameters, for certain example embodiments that utilize a pulsed laser source. 
         FIG. 56  illustrates an example algorithm for controlling the radiation source and scanning system motor in a scanned-beam treatment device, according to certain example embodiments. 
         FIG. 57A  illustrates a more specific algorithm for controlling parameters of the scanning motor and radiation source in a scanned-beam treatment device, according to an example embodiment. 
         FIG. 57B  illustrates radiation pulse parameters with respect to a rotating beam-scanning element, e.g., for the example control algorithm shown in  FIG. 56 , according to an example embodiment. 
         FIGS. 58 and 59  illustrate electrical schematics for two independent laser current switch controls of an example laser-based treatment device, including a first digital control circuit connected to the laser anode side ( FIG. 58 ) and a second dimmer-type control circuit connected to the cathode side ( FIG. 59 ). 
         FIG. 60  illustrates a three-dimensional cross-section of a volume of skin for illustrating the process of a non-ablative fractional treatment. 
         FIG. 61  illustrates an example scanned-beam radiation-based treatment device, according to one example embodiment. 
         FIGS. 62A-62B  illustrate an example arrangement of components for an example scanned-beam treatment device including a cup-shaped rotating scanning element, according to an example embodiment. 
         FIG. 63  illustrates an example arrangement of components for an example scanned-beam treatment device including a cup-shaped rotating scanning element, according to another example embodiment. 
         FIGS. 64A-64D  illustrate an example arrangement of components for an example scanned-beam treatment device including a cup-shaped rotating scanning element, according to an yet example embodiment. 
         FIGS. 65A-65D  illustrate an example arrangement of components for an example scanned-beam treatment device including a disk-shaped rotating scanning element, according to an example embodiment. 
         FIGS. 66A and 66B  illustrate the optical system and its affects on the fast axis beam profile ( FIG. 66A ) and slow axis beam profile ( FIG. 66B ) for embodiments of the device according to  FIGS. 64A-64D  or  FIGS. 65A-65D  that omit a downstream lens. 
         FIGS. 67A and 67B  illustrate the optical system and its affects on the fast axis beam profile ( FIG. 67A ) and slow axis beam profile ( FIG. 67B ) for embodiments of the device according to  FIGS. 64A-64D  or  FIGS. 65A-65D  that include a downstream lens. 
         FIGS. 68A-68C  illustrate an example arrangement of components ( FIGS. 68A and 68B ) and an assembled view of such components within a device housing ( FIG. 68C ) for an example scanned-beam treatment device, according to an another example embodiment. 
         FIGS. 69A and 69B  illustrate the optical system and its affects on the fast axis beam profile ( FIG. 69A ) and slow axis beam profile ( FIG. 69B ) for an embodiment of the device according to  FIGS. 68A-68C  that omits a downstream lens. 
         FIGS. 70A and 70B  illustrate the optical system and its affects on the fast axis beam profile ( FIG. 70A ) and slow axis beam profile ( FIG. 70B ) for an embodiment of the device according to  FIGS. 68A-68C  that includes a downstream lens. 
         FIG. 71  illustrates a graph and cross-sectional representation of the fast axis and slow axis beam profile of a delivered beam, illustrating the focal plane with respect to the surface of the skin, according to certain example embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Some embodiments of the disclosure may be understood by referring, in part, to the following description and the accompanying drawings, in which like reference numbers refer to the same or like parts. 
       FIG. 1  illustrates various components of an example held-held radiation-based treatment device  10 , according to certain embodiments. Radiation-based treatment device  10  may include a radiation source  14  including a radiation source  14  configured to generate an energy beam, an optical system  15  for scanning, conditioning, and/or delivering a series of scanned energy beams to a treatment area of the skin  40 , control systems  18 , one or more power supplies  20 , and/or one or more fans  34 . 
     In some embodiments, the main components of device  10  may be substantially self-contained in a held-held structure or outer housing  24 . Held-held housing  24  may define an application end (or “treatment tip”)  42  configured to be placed in contact with the skin (or other target surface) during treatment of a treatment area of the skin  40 . Application end  42  may include or house various user interfaces, including the treatment delivery interface for delivering scanned beams to the user, as well as one or more sensors  26  for detecting various characteristics of the skin (or other surface) and/or energy delivered by device  10 . In some embodiments, application end  42  may include an aperture or window  44  through which the scanned beams are delivered to the target surface, or alternatively, an optical element  16  (e.g., a lens) may be located at application end  42  and configured for direct contact or close proximity with the skin during treatment. 
     Device  10  may include any other components suitable for providing any of the functionality discussed herein or other related functionality known to one of ordinary skill in the art. 
     Radiation source  14  may include one or more radiation sources  14 , such as one or more lasers, LEDs, and/or flashlamps, ultrasound devices, RF devices, or microwave emitters, for example. Embodiments including lasers as the radiation source  14  may include any type or types of lasers, e.g., one or more edge emitting laser diodes (single emitter edge emitting laser diodes or multiple emitter edge emitting laser diodes), laser diode bars, VCSEL lasers (Vertical Cavity Surface Emitting Lasers), CO2 lasers, Erbium YAG lasers, pulsed dye lasers, fiber lasers, other types of lasers, or any combination thereof. 
     Radiation source  14  may include one or more radiation source, each operable to generate a beam of radiation. For example, radiation source  14  may comprise one or more laser sources, e.g., one or more laser diodes, CO2 lasers, Erbium YAG lasers, pulsed dye lasers, fiber lasers, etc. In some embodiments, radiation source  14  may comprise one or more single-emitter edge emitting laser diode, multi-emitter edge emitting laser diode (e.g., as described in co-pending U.S. patent application Ser. No. 13/426,995 filed Mar. 21, 2012 and entitled “Dermatological Treatment Device with One or More Multi-Emitter Laser Diode,” the entire contents of which application are hereby incorporated by reference), laser diode bars, or VCSEL lasers. In some embodiments, radiation source  14  may comprise one non-laser sources, e.g., one or more LEDs or flashlamps, for example. 
     For the sake of simplicity, this disclosure often refers to a singular radiation source or laser source (e.g., “a radiation source,” “the radiation source,” “a laser,” or “the laser”), or to a device including a single radiation source or a single laser source. However, it should be understood that unless explicitly stated otherwise, any reference herein to a single radiation source is intended to mean at least one radiation source or laser source. Thus, for example, disclosure herein of a device including a laser source that generates a beam should be interpreted as disclosing a device including a singular laser source that generates a single beam, as well as a device including multiple laser sources each generating a respective beam. 
     In some embodiments, the beam emitted from the radiation source diverges in at least one direction. For example, in embodiments including an edge emitting laser diode or multi-radiation source laser diode bar, the emitted beam may diverge in both a fast axis and a slow axis. Thus, in such embodiments, optical system  15  may include optics directed to the fast axis and the slow axis beam profiles, either together or independently, as discussed below in greater detail. In embodiments including a VCSEL laser, the emitted beam or beams may diverge symmetrically in both axes. 
     In some embodiments, radiation source  14  may be configured for and/or operated at any suitable wavelength to provide the desired dermatological treatment. For example, radiation source  14  may be a laser configured for and/or operated at a wavelength that is absorbed by water in the skin, e.g., between 1400 nm and 2000 nm, e.g., for certain photothermolysis or other treatments. In some embodiments, radiation source  14  may be a laser configured for and/or operated at a wavelength of between 1400 nm and 1550 nm, e.g., for acne treatment or certain fractional non-ablative skin treatments, e.g., skin rejuvenation or resurfacing, wrinkle treatment, or treatment of pigmented legions (e.g., age spots, sun spots, moles, etc.). In other embodiments, radiation source  14  may be a laser configured for and/or operated at a wavelength of between 1700 nm and 1800 nm, e.g., for sebaceous gland related treatment like acne. In still other embodiments, radiation source  14  may be a laser configured for and/or operated at a wavelength of about 1926 nm, e.g., for pigmented lesion treatment like solar lentigo. As another example, radiation source  14  may be a laser configured for and/or operated at a wavelength of about 810 nm for providing hair removal treatment or melanin-based treatments. In some embodiments that include multiple radiation sources, different radiation sources may emit light at different wavelengths. For example, a device may include one or more first radiation sources that emit a wavelength of about 1400 nm-1550 nm and one or more second radiation sources that emit a wavelength of about 1926 nm. As another example, the wavelength may be in the UV (e.g., such as to effect DNA or micro-organisms), may be in the visible spectrum (e.g., such as to affect melanin, hemoglobin, oxyhemoglobin, or photosensitive elements like mitochondria or fibroblasts) or in the IR spectrum (e.g., such as to affect melanin, water, lipids). Likewise, the radiation may be in the ultrasound spectrum (e.g., such as to perform focused ultrasound fractional skin rejuvenation or tightening) or in the radio frequency spectrum (e.g., such as to perform fractional or bulk heating). 
     Radiation source  14  may be configured for or operated at any suitable energy or power level. For example, in some embodiments, radiation source  14  may emit a total energy of between about 2 mJ and about 30 mJ per delivered beam (i.e., per treatment spot). For example, radiation source  14  may emit between about 5 mJ and about 20 mJ per delivered beam. In particular embodiments, radiation source  14  emits about 10-15 mJ per delivered beam. In some embodiments, each delivered beam results from a pulse of a pulsed radiation source, which pulse is then scanned by an automated scanning system  48  to provide an output beam that is delivered to the skin as a delivered beam. Thus, in such embodiments, radiation source  14  may emit a total energy of between about 2 mJ and about 30 mJ per pulse, e.g., between about 5 mJ and about 20 mJ per pulse, e.g., about 10-15 mJ per pulse. 
     In some embodiments, device  10  controls radiation source  14  to generate radiation as continuous wave (CW) radiation, pulsed radiation, or in any other manner, depending on the particular embodiment, application, or device setting. For the purposes of this disclosure, pulsed or continuous wave radiation refers to the radiation emitted by radiation source  14 , not the radiation delivered to the skin, as the radiation emitted by radiation source  14  is scanned to different locations by the automated scanning system  48 . Thus, in some embodiments, radiation generated as CW radiation is delivered to the skin essentially as a series of pulses at different locations, as the CW radiation is rapidly scanned to different distinct treatment spots on the skin, with each treatment spot receiving a brief duration of the CW radiation, which is essentially a pulse. Thus, in embodiments that employ a scanning system, both CW and pulsed radiation sources may deliver energy in a pulsed manner. 
     Thus, to clarify the discussion, as used herein, a “generated pulse” refers to a pulse emitted by a pulsed radiation source  14 , while a “delivered pulse” refers to a pulse delivered out of the application end  42  of the device  10 . A delivered pulse is also referred to herein as a delivered beam  114 , which is defined as the radiation output from one deflection sector of the relevant scanning element and delivered out of the application end  42  of the device  10 , during any one particular scan of the scanning element. Thus, delivered pulses may be provided by both CW and pulsed radiation sources. A delivered pulse may include a single, continuous delivery of radiation, or multiple high-frequency pulses (e.g., in the form of a modulated pulse, pulse train, or super pulse) output from one deflection sector of the scanning element and delivered out of application end  42  during any one particular scan of the scanning element. 
     Embodiments in which radiation source  14  generates pulsed radiation may utilize any suitable pulse parameters, e.g., pulse rate or frequency, pulse on time, pulse off time, duty cycle, pulse profile, etc. In some embodiments, radiation source  14  may be pulsed at a rate between 0.5 and 75 Hz. For example, radiation source  14  may be pulsed at a rate between 2 and 30 Hz. In particular embodiments, radiation source  14  may be pulsed at a rate between 10 and 20 Hz, e.g., about 15 Hz. The energy per pulse on a given treatment spot can be achieved by a single pulse or by multiple repetitive pulses. 
     As used herein, a “treatment spot” means a contiguous area of skin irradiated by a radiation source—during a delivered pulse (as defined above)—to a degree generally sufficient to provide a desired treatment in the skin at that location. For some types of radiation source, including laser radiation sources for example, the boundaries of the treatment spot are defined by the “1/e 2  width,” i.e., the treatment spot includes a contiguous area of the skin surface that is irradiated by a radiation intensity equal to at least 1/e 2  (or 0.135) times the maximum radiation intensity at any point on the skin surface. A treatment spot may include the full extent of the surface (or volume) irradiated. A treatment spot may include the full extent of the tissue being influenced by the irradiation, which may be smaller than the irradiated area or volume, or may be larger (e.g., due to thermal conductivity). Further, reference to a treatment spot “on the skin” or similar language refers to radiation pattern on the skin which generally produces a radiation pattern within the skin, whether or not it produces a treatment effect on the surface of the skin. 
     A treatment spot includes any increased areas due to smearing, blurring, or other elongation in any one or more direction due to movement of device  10  across the skin during a delivered pulse, e.g., in a gliding mode operation of device  10 . For example, due to smearing or blurring effects, the treatment spot generated by each delivered beam  114  may be 10% to 500% larger than the size of the instantaneous irradiated area of skin by that delivered beam  114 , depending on a number of factors. 
     Optical system  15  is configured for scanning, delivering, conditioning, and/or otherwise controlling or affecting radiation from radiation source  14  to the target surface (e.g., the skin), and may include any number and/or type(s) of optics, or optical elements,  16  for providing such functionality. In some embodiments, optical system  15  includes (a) a beam scanning system  48  including any suitable optics  16  configured to convert, or “scan,” an input beam (e.g., a pulsed or CW input beam) into a successive series of output beams for delivery to the skin, and (b) any other optical elements  16  (if any) upstream and/or downstream of the scanning system  48 . The optics  16  of scanning system  48  are referred to herein as scanning optics  62 , while the other optics  16  of optical system  15  (if any) are referred to herein as non-scanning optics  60 , as discussed in more detail below with reference to  FIG. 3A . 
     As used herein, an “optic” or “optical element” may mean any reflective or transmissive element that influences the angular distribution profile (e.g., angle of convergence, divergence, or collimation) of a beam in at least one axis, influences the focus of the beam in at least one axis, influences the propagation direction of the beam (e.g., by reflection or deflection), or otherwise affects a property of the radiation. Thus, optics include planar and non-planar reflective elements such as mirrors and other reflective surfaces, as well as transmissive elements such as lenses, prisms, light guides, gratings, filters, etc. For the purposes of this disclosure, optics do not generally include planar or substantially planar transmissive elements such as transmissive windows or films, e.g., a window or film that serves as a transmissive aperture for protecting internal components of the device. Reference herein to “optics” or “optical elements” means one or more optical elements. 
     Controls 
     Control systems  18  may be configured to control one or more components of device  10  (e.g., radiation source  14 , beam scanning system  48 , fan  34 , displays  32 , etc.). Control systems  18  may include, for example, any one or more of the following: a radiation source control system for controlling aspects of the generation, treatment, and delivery of radiation to the user; a scanning system control system for controlling automated scanning system  48  for scanning a beam to generate a pattern of treatment spots on the area; a displacement-based control system for controlling aspects of device  10  based on the determined displacement of device  10  across to the skin (e.g., as device is glided across the skin during treatment), e.g., relative to a prior treatment position; a temperature control system; an eye safety control system to help prevent exposure of the eyes (e.g., the cornea) to the treatment radiation (an eye safety control system may be omitted in embodiments in which the laser radiation emitted from device  10  is inherently eye-safe, e.g., certain direct exposure embodiments of device  10 ); and/or a battery/power control system. 
     Control systems  18  may include one or more sensors  26  and/or user interfaces  28  for facilitating user interaction with device  10 , and control electronics  30  for processing data (e.g., from sensors  26  and/or user interfaces  28 ) and generating control signals for controlling various components of device  10 . Control electronics  30  may include one or more processors and memory devices for storing logic instructions or algorithms or other data. Memory devices may include any one or more device for storing electronic data (including logic instructions or algorithms), such as any type of RAM, ROM, Flash memory, or any other suitable volatile and/or non-volatile memory devices. Logic instructions or algorithms may be implemented as software, firmware, or any combination thereof. Processors may include any one or more devices, e.g., one or more microprocessors and/or microcontrollers, for executing logic instructions or algorithms to perform at least the various functions of device  10  discussed herein. Control electronics  30  may include exclusively analog electronics or any combination of analog and digital electronics. 
     Control systems  18  may control components or operational parameters of device  10  based on feedback from sensors  26 , user input received via user interfaces  28 , and/or logic instructions/algorithms. For example, control systems  18  may control the treatment level (e.g., low power level, medium power level, or high power level) or treatment mode (e.g., gliding mode vs. stamping mode; or rapid-pulse mode vs. slow-pulse mode; or initial treatment mode vs. subsequent treatment mode; etc.), the status of radiation source  14  (e.g., on/off, pulse-on time, pulse-off time, pulse duty cycle, pulse frequency, temporal pulse pattern, etc.), parameters of the radiation (e.g., radiation wavelength, intensity, power, fluence, etc.), the configuration or operation of one or more optical elements (e.g., the operation of a rotating-element beam scanning system  48 , as discussed below), and/or any other aspects of device  10 . In some embodiments, control systems  18  may control the operation of radiation source  14  and/or component(s) of beam scanning system  48  (e.g., a rotating scanning element) based at least on feedback from a displacement sensor. Thus, for example, control systems  18  may control radiation source  14  and/or a rotating scanning element based on signals from a displacement sensor indicating that device  10  or treatment tip  42  has been translated a certain distance across treatment area  40  from a prior treatment position. 
     Sensors  26  may include any one or more sensors or sensor systems for sensing or detecting data regarding device  10 , the user, the operating environment, or any other relevant parameters. For example, as discussed in greater detail below with respect to  FIG. 2 , sensors  26  may include one or more of the following types of sensors: (a) one or more displacement sensor for determining the displacement of device  10  relative to the skin, (b) one or more motion/speed sensor for determining the speed, rate, or velocity of device  10  moving (“gliding”) across the skin, (c) an encoder sensor for monitoring the speed of a motor of the beam scanning system  48  and/or the position of a rotating scanning element), (d) one or more skin-contact sensor for detecting proper contact between device  10  and the skin, (e) one or more pressure sensor for detecting the pressure of device  10  pressed against the skin, (f) one or more temperature sensor for detecting the temperature of the skin and/or components of device  10 , (g) one or more radiation sensor for detecting one or more parameters of radiation (e.g., intensity, fluence, wavelength, etc.) delivered or indicative of delivered to the skin, (h) one or more color/pigment sensor for detecting the color or level of pigmentation in the skin, (i) one or more eye safety sensor for preventing unwanted eye exposure to light from radiation source  14 , (j) one or more dwell sensor for detecting if the device is stationary or essentially stationary with respect to the skin, (k) one or more roller-type sensors for detecting the displacement and/or glide speed of the device, and/or any (l) other suitable types of sensors. 
     User interfaces  28  may include any systems for facilitating user interaction with device  10 . For example, user interfaces  28  may include buttons, switches, knobs, sliders, touch screens, keypads, devices for providing vibrations or other tactile feedback, speakers for providing audible instructions, beeps, or other audible tones; or any other methods for receiving commands, settings, or other input from a user and providing information or output to the user. User interfaces  28  may also include one or more displays  32 , one or more of which may be touch screens for receiving user input. One or more user interfaces  28  or portions thereof may be included in a separate housing from the treatment device, such as in a smart charging dock or a personal computer, and the treatment device may communicate with the separate housing via hardwire (such as a cable or jack), wireless methods (such as infrared signals, radio signals, or Bluetooth), or other suitable communication methods. 
     Power supplies  20  may include any one or more types and instances of power supplies or power sources for generating, conditioning, or supplying power to the various components of device  10 . For example, power supplies  20  may comprise one or more rechargeable or non-rechargeable batteries, capacitors, super-capacitors, DC/DC adapters, AC/DC adapters, and/or connections for receiving power from an outlet (e.g., 110V wall outlet). In some embodiments, power supplies  20  include one or more rechargeable or non-rechargeable batteries, e.g., one or more Li containing cells or one or more A, AA, AAA, C, D, prismatic, or 9V rechargeable or non-rechargeable cells. In one example embodiment, device  10  uses an LiFePO4 18650XP, 3.2V, 1100 mAh rechargeable battery from Shenzhen Mottcell Battery Techology Co., China. 
       FIG. 2  illustrates example components of control systems  18  for controlling aspects of device  10 , according to certain embodiments. Control systems  18  may include control electronics  30 , sensors  26 , user interfaces  28 , and a number of control subsystems  52 . Control subsystems  52  are configured to control one or more components of device  10  (e.g., radiation source  14 , fans  34 , displays  32 , etc.). In some embodiments, control subsystems  52  may include a radiation source control system  128 , a scanning system control system  130 , a displacement-based control system  132 , a usability control system  133 , a user interface control system  134 , a temperature control system  136 , a battery/power control system  138 , a motor/pulse control system  139 , and/or any other suitable control systems for controlling any of the functionality disclosed herein. User interface control system  134  may include a user interface sensor control system  140  and a user input/display/feedback control system  142 . 
     Each control subsystem  52  may utilize any suitable control electronics  30 , sensors  26 , user interfaces  28 , and/or any other components, inputs, feedback, or signals related to device  10 . Further, any two or more control systems may be at least partially integrated. For example, the functionality of control systems  128 - 139  may be at least partially integrated, e.g., such that certain algorithms or processes may provide certain functionality related to multiple or all control systems  128 - 139 . 
     Each control subsystem  52  (e.g., subsystems  128 - 139 ) may be configured to utilize any suitable control electronics  30 , sensors  26 , and user interfaces  28 . In some embodiments, control electronics  30  may be shared by more than one, or all, control subsystems  52 . In other embodiments, dedicated control electronics  30  may be provided by individual control subsystems  52 . 
     Control electronics  30  may include one or more processors  144  and memory device  146  for storing logic instructions or algorithms  148  or other data. Memory devices  146  may include any one or more device for storing electronic data (including logic instructions or algorithms  148 ), such as any type of RAM, ROM, Flash memory, or any other suitable volatile and/or non-volatile memory devices. Logic instructions or algorithms  148  may be implemented as hardware, software, firmware, or any combination thereof. Processors  144  may include any one or more devices, e.g., one or more microprocessors and/or microcontrollers, for executing logic instructions or algorithms  148  to perform at least the various functions of device  10  discussed herein. Control electronics  30  may include exclusively analog electronics or any combination of analog and digital electronics. 
     Sensors  26  may include any one or more sensors or sensor systems for sensing or detecting data regarding device  10 , the user, the operating environment, or any other relevant parameters. For example, sensors  26  may include one or more of the following types of sensors:
         (a) At least one displacement sensor  200  for detecting, measuring, and/or calculating the displacement of device  10  relative to the skin  40 , or for generating signals from which the displacement is determined. In some embodiments, e.g., as discussed below with reference to  FIGS. 40A-44 , displacement sensor  200  may be a single-pixel sensor configured to determine a displacement of device  10  by identifying and counting intrinsic skin features in the skin. In other embodiments, e.g., as discussed below with reference to  FIGS. 45-46 , displacement sensor  200  may be a multiple-pixel sensor, such as a mouse-type optical imaging sensor utilizing a two-dimensional array of pixels.       

     In other embodiments, e.g., as discussed below with reference to  FIGS. 48A-48G , displacement sensor  200  may be a roller-type sensor  218  in which the amount of roller rotation indicates the linear displacement of the device. For example, a roller-type sensor displacement sensor  200  may include a mechanical roller having one or more indicia, a detection device (e.g., an optical or other scanner) for identifying such indicia as they roll past the detection device, and processing electronics for determining the displacement of device  10  based on the detection of such indicia. In some embodiment, the roller may also be actively driven by a motor to facilitate a gliding treatment. 
     In still other embodiments, displacement sensor  200  may comprise a capacitive sensor, as described below. Displacement sensor  200  may use any number of other devices or techniques to calculate, measure, and/or calculate the displacement of device  10 . 
     Displacement sensor  200  may be used for (i) detecting, measuring, and/or calculating linear displacements of device  10  in one or more directions, (ii) detecting, measuring, and/or calculating the degree of rotation travelled by device  10  in one or more rotational directions, or (iii) any combination thereof.
         (b) At least one motion/speed sensor  202  for detecting, measuring, and/or calculating the rate, speed, or velocity of device  10  moving across the treatment area  40  (the “manual glide speed”), or for generating signals from which the manual glide speed is determined;   (c) At least one encoder sensor  203  for detecting the rotation and/or position of an encoder fixed to a scanning system motor  120  (e.g., encoder wheel  121  shown in  FIGS. 68A and 68B ). For example, encoder sensor  203  may be an optical sensor configured to read the rotation and/or position of the encoder as the encoder is rotated by motor  120 . The signal from encoder sensor  203  can be used for determining the motor speed and/or the position of a rotating scanning element, e.g., for controlling the timing of beam pulses delivered to the scanning element.   (d) At least one skin-contact sensor  204  for detecting contact between device  10  and the skin or treatment area  40 . For example, device  10  may include one or more capacitive contact sensors  204  for detecting contact with the user&#39;s skin.   (e) At least one pressure (or force) sensor  206  for detecting the pressure (or force) of device  10  against the skin or treatment area  40 .   (f) At least one temperature sensor  208  for detecting the temperature of the treatment area  40 , a region of the treatment area  40  (such as the treatment spot  70  before, during, and/or after treatment), components of device  10 , or other object.   (g) At least one radiation sensor  210  for detecting levels or other parameters of radiation delivered to the treatment area  40  or indicative of the radiation delivered to the treatment area  40  (e.g., per light pulse, per individual beam/treatment spot, per delivered array of scanned beams/treatment spots  70 , per a specific number of individual delivered beams/treatment spots  70  or scanned arrays of beams/treatment spots  70 , or per a specific time period). For example, device  10  may include a photodiode to measure the pulse duration of the treatment beam.   (h) At least one color/pigment sensor  212  for detecting the color or level of pigmentation in the treatment area  40 .   (i) At least one eye safety sensor  214  for helping to prevent unwanted eye exposure to light from the treatment radiation source  14 . Example eye safety sensors  214  are discussed below with reference to  FIGS. 48-51 .   (j) At least one dwell sensor  216  for detecting whether device  10  is stationary or essentially stationary with respect to the skin.   (k) At least one roller-based sensor  218  that may be used as a displacement sensor  200 , a motion/speed sensor  202 , a dwell sensor  216  or all, for detecting signals indicative of the displacement of device  10 , the manual glide speed of device  10 , or stationary status of device  10 , or both.   (l) any other type of sensors.       

     User interfaces  28  may include any systems for facilitating user interaction with device  10 , e.g., displaying data or providing feedback to a user visually and/or audibly, and/or palpably (e.g., via vibration), and receiving commands, selections, or other input from the user. For example, user interfaces  28  may include one or more displays  32  (one or more of which may be interactive touch screens), one or more manual devices  220  (e.g., buttons, switches, knobs, sliders, touch screens, keypads, etc.), one or more speakers  222 , and/or any other devices for providing data, information, or feedback to a user or receiving input or information from a user. 
     Control subsystems  52  may be configured to control one or more controllable operational parameters of device  10 , based on feedback from sensors  26 , user input received via user interfaces  28 , and/or execution of logic instructions/algorithms  148 . As used herein, “controllable operational parameters” may include any aspects or parameters of device  10  that may be controlled by any of control subsystem  52 . 
     For example, one or more control subsystems  52  may control any aspects of the operation of radiation source  14 , such as for example:
         (a) selecting and/or switching the treatment mode (discussed below),   (b) controlling the on/off status of radiation source  14  (which may involve controlling individual light sources separately or as a group), and the timing of such on/off status: e.g., pulse trigger delay, pulse duration, pulse duty cycle, pulse frequency, temporal pulse pattern, etc.,   (c) controlling one or more parameters of the radiation: e.g., wavelength, intensity, power, fluence, etc. (e.g., by controlling the power supplied to radiation source  14 ), and/or   (d) controlling any other aspect of radiation source  14 .       

     As another example, one or more control subsystems  52  may control any aspects of the operation of scanning system  48 , such as for example:
         (a) controlling the starting/stopping of rotation of a rotating scanning element  100 ,   (b) controlling the rotational speed of rotating scanning element  100  (e.g., by controlling motor  120 ), and/or   (c) controlling any other aspect of scanning system  48 .       

     Control subsystems  52  (e.g., control systems  128 - 139 ) may control components or aspects of device  10  based on feedback from sensors  26 , user input received via user interfaces  28 , and/or logic instructions/algorithms  148 . For example, in some embodiments, control system  128  may control the operation of radiation source  14  and/or beam scanning system  48  (e.g., the rotation of a scanning element  100 ) based on feedback from one or more displacement sensors  200  and/or skin contact sensors  204 . As another example, control system  128  may control the operation of radiation source  14  and/or beam scanning system  48  based on feedback from one or more displacement sensors  200 , skin contact sensors  204 , and eye safety sensors  214 . In other embodiments, control system  128  may control the operation of radiation source  14  and/or beam scanning system  48  based on feedback from one or more glide rate sensors  202  and skin contact sensors  204 . In other embodiments, control system  128  may control the operation of radiation source  14  and/or beam scanning system  48  based on feedback from one or more dwell sensors  216  and skin contact sensors  204 . In other embodiments, control system  128  may control the operation of radiation source  14  and/or beam scanning system  48  based on feedback from both a displacement sensor  200  or dwell sensor  216  and a glide rate sensor  202 , in addition to one or more other sensors  204 - 218 . 
     Optical System 
     As discussed above, device  10  may include an optical system  15  configured for scanning, delivering, conditioning, and/or otherwise controlling or affecting radiation from radiation source  14  to the target surface (e.g., the skin), and may include any number and/or type(s) of optics, or optical elements,  16  for providing such functionality. Optical system  15  may include (a) a beam scanning system  48  including any suitable beam scanning optics  62  for scanning an input beam to generate a successive series of output beams for delivery to the skin, and (b) any other optical elements  16  (if any) upstream and/or downstream of the scanning system  48 . 
       FIG. 3A  illustrates aspects of the general components of an example optical system  15  for device  10 , according to certain embodiments. In such embodiments, optical system  15  may include beam scanning optics  62  of beam scanning system  48  and (optionally) non-scanning optics  60 . Beam scanning optics  62  may be configured to scan an input beam into a sequentially-delivered series or array of output beams to create a pattern of treatment spots  70  (e.g., spots, lines, or other shapes) in the target area  40 . Non-scanning optics  60  (if any) may include non-scanning optics  60 A upstream of scanning optics  62 , non-scanning optics  60 B downstream of scanning optics  62 , or both upstream non-scanning optics  60 A and downstream non-scanning  60 B. Some embodiments include upstream non-scanning optics  60 A and no downstream non-scanning optics  60 B. 
     With reference to  FIG. 3A , a beam generated by radiation source  14  is referred to herein as a generated beam  108 . At the point of being received at scanning optics  62 , the beam is referred to herein as an input beam  110 . The scanning optics  62  scan the input beam  110  into a plurality of scanned beams referred to herein as output beams  112 . At the point of exiting the application end  42  of device  10 , the scanned beams are referred to herein as delivered beams  114 . 
       FIG. 3B  illustrates aspects of the general components of an example optical system  15  for device  10 , according to certain embodiments. In particular,  FIG. 3B  illustrates that optics  16  may include axis-asymmetric elements that act on different optical axes of an incident beam differently. For example, optics  16  may include first optics configured to influence an incident beam primarily in a first optical axis, and second optics configured to influence the beam primarily in a second optical axis orthogonal to the first axis. Influencing the beam primarily in a particular optical axis may include affecting the intensity profile of the beam in the particular optical axis to a greater extent than in an orthogonal optical axis. As used herein, the intensity profile of the beam along a particular optical axis refers to (a) the shape of the intensity profile along the particular optical axis (e.g., Gaussian, flat-topped, etc.); (b) whether the beam is converging, diverging, or collimated; (c) the degree of convergence or divergence of the beam; etc. 
     In some embodiments, such axis-asymmetric optical elements are used for controlling or treating a radiation source  14  that generates an asymmetric beam, e.g., a laser diode, which generates a generally rectangular cross-sectioned beam that diverges relatively quickly in a first axis (referred to as the “fast axis”) and diverges relatively slowly in an orthogonal second axis (referred to as the “slow axis”). 
     Thus, in the example shown in  FIG. 3B , non-scanning optics  60  include separate fast axis optics  64  (or fast axis optics  64 ) and slow axis optics  66  (or slow axis optics  66 ). Fast axis optics  64  include one or more optical elements  16  configured to primarily affect the fast axis intensity profile of the beam (as compared with the effects on the slow axis intensity profile), while slow axis optics  66  include one or more optical elements configured to primarily affect the slow axis intensity profile of the beam (as compared with the effects on the fast axis intensity profile). In certain embodiments, fast axis optics  64  are configured to affect the fast axis intensity profile without substantially affecting the slow axis intensity profile. Further, in certain embodiments, slow axis optics  66  are configured to affect the slow axis intensity profile without substantially affecting the fast axis intensity profile. In particular embodiments, both of these features are provided: fast axis optics  64  affect the fast axis intensity profile without substantially affecting the slow axis intensity profile, and slow axis optics  66  affect the slow axis intensity profile without substantially affecting the fast axis intensity profile. 
     Alternatively, fast axis optics  64  and slow axis optics  66  may be partially or fully integrated. For example, a particular optical element (e.g., mirror or lens) may significantly affect both the fast axis and slow axis intensity profiles. Such element may be referred to as a multi-axes optical element, and may or may not be symmetrical about all axes (e.g., spherical). Some embodiments may include one or more multi-axes optical elements, along with one or more separate fast axis optical elements; or one or more multi-axis optical elements, along with one or more separate slow axis optical elements; one or more multi-axis optical elements, along with one or more separate slow axis optical elements and one or more separate fast axis optical elements; or any other combination thereof. 
     Fast axis optics  64 , slow axis optics  66 , and beam scanning optics  62  may be arranged in any order along the path of the beam propagation. For example, optics  64  and  66  may be arranged upstream of beam scanning optics  62 , or downstream of beam scanning optics  62 , or beam scanning optics  62  may be arranged between optics  64  and  66 , beam scanning optics  62  may act as either one or both of optics  64  and  66 . Further, where beam scanning optics  62  also acts as a fast axis optic  64 , a slow axis optic  66 , or both, optical system  15  may also include one or more separate fast axis optic  64 , slow axis optic  66 , or both, respectively 
     Further, each of fast axis optics  64  and slow axis optics  66  may be separate from, or integral with, beam scanning optics  62 . In other words, scanning optics  62  may influence either one, both, or neither of the fast axis and slow axis intensity profiles. Thus, for example, scanning optics  62  may act as fast axis optics  64 , with slow axis optics  66  being provided separately. Alternatively, scanning optics  62  may act as slow axis optics  66 , with fast axis optics  64  being provided separately. Alternatively, scanning optics  62  may significantly affect both the fast axis and slow axis intensity profiles. 
       FIG. 3C  illustrates the general configuration of an example optical system  15  for particular example embodiments of device  10 . In this example configuration, optical system  15  includes an upstream fast axis optic  60 A,  64 ; a beam scanning optic  62  that also act as slow axis optics  66 , and optionally (depending on the particular embodiment) a downstream fast axis optic  60 B. Upstream fast axis optic  60 A and optional downstream fast axis optic  60 B may each comprise, for example, a cylindrical or “rod” lens, an aspheric lens, or any other suitable optical element. Beam scanning optic  62 , which also acts as a slow axis optic  66 , may comprise, for example, a rotating multi-sector scanning element, e.g., scanning element  100 A or  100 B discussed below. Optical system  15  may also include one or more planar mirrors configured to direct the beams as desired. For example, a planar mirror may be positioned downstream of beam scanning optic  62  (and upstream of downstream fast axis lens  60 B, if present) to direct the scanned array of output beams  112  toward the application end  42  of device  10 . 
     In particular embodiments, radiation source  14  is a laser diode configured to emit a pulsed or CW generated beam  108 . Upstream fast axis optic  60 A reduces the divergence of the generated beam  108  in the fast axis, and the resulting input beam  110  is received at the beam scanning optic  62 , which scans the input beam  110  to produce a sequential series of output beams  112 . In some embodiments, the output beams  112  may be redirected by one or more planar mirrors (e.g., as shown in  FIG. 3D , discussed below) and/or further influenced by downstream fast axis optic  60 B. In other embodiments, the output beams  112  may be delivered to the skin as delivered beams  114 , without any optics  16  downstream of scanning optic  62 . 
     In some embodiments, the scanning optic  62  (e.g., scanning element  100 A or  100 B discussed below) may provide a sequential array of output beams  112  that are angularly offset from each other in a scan direction. The optional downstream fast axis optic  60 B may extend in the scan direction in order to receive and act on the array of output beams  112 . For example, fast axis optic  60 B may comprise a rod lens extending in the scan direction and configured to reduce the divergence/increase the convergence of each output beam  112  for delivery to the skin as a delivered beam  114 . 
       FIG. 3D  illustrates a configuration similar to the configuration shown in  FIG. 3C , but further including a planar turning mirror  65 , according to example embodiments. In some such embodiments, the scanning optic  62  (e.g., scanning element  100 A or  100 B discussed below) may provide a sequential array of output beams  112  that are angularly offset from each other in a scan direction. The scan direction of the output beams  112  may be shifted, or turned, by mirror  65 . The optional downstream fast axis optic  60 B may extend in the same direction as the shifted or turned scan direction in order to receive and act on the array of output beams  112 . For example, fast axis optic  60 B may comprise a rod lens extending in the scan direction and configured to reduce the divergence/increase the convergence of each output beam  112  for delivery to the skin as a delivered beam  114 . 
     In addition, other embodiments discussed below relate to various configurations of optical system  15 . For instance, in the example embodiments shown in  FIGS. 10A-11B , beam scanning optics  62  also act as slow axis optics  66 , while fast axis optics  64  are provided separately. In the example embodiments shown in  FIGS. 19 and 20 , both fast axis optics  64  and slow axis optics  66  are provided separately from beam scanning optics  62 . 
     As discussed above, the term “optics” as used herein may include a single optical element or multiple optical elements. In some embodiments, e.g., the example embodiments shown in  FIGS. 10A-10B, 11A-11B, 19, and 20 , device  10  includes only a single fast axis optical element  64  and a single slow axis optical element  66 . Also, embodiments according to  FIG. 3C  in which downstream fast axis optics  60 B are omitted include only a single fast axis optical element  64  and a single slow axis optical element  66 . In these embodiments, beam scanning optic  62  acts as the slow axis optic  66  (e.g., each sector of the rotating multi-sector scanning element  62  influences the input beam  110  primarily in the slow axis, such that at any particular position of the rotating scanning element  62 , a beam from generation  108  to delivery  114  is significantly affected in the slow axis by only a single optical element: the respective sector of the rotating scanning element  62 . Such embodiments also include a single fast axis optical element  64  separate from the scanning optic  62 . 
     In the embodiments of  FIGS. 19 and 20 , the fast axis optical element  64  and slow axis optical element  66  are separate from the scanning optic  62 , which utilizes planar mirror facets and thus does not influence the beam in either the fast or slow axis except for planar deflection. 
     In other embodiments, device  10  includes more than one fast axis optical element  64 , more than one slow axis optical element  66 , or both. For example, any of the embodiments shown in  FIGS. 10A-10B, 11A-11B, 19, and 20  may further include one or more fast-axis optical elements  64  and/or slow-axis optical elements  66  to further influence the beam in the respective axes. 
     In still other embodiments, device  10  includes one or more axis-symmetric optics  16 , in place of, or in addition to, fast axis optics  64  and/or slow axis optics  66 . For example, optics  16  of optical system  15  may include one or more spherical optical elements, axis-symmetrical parabolic optical elements, and/or any other type of axis-symmetric optical elements. Such axis-symmetric optical elements may be used, for example, in embodiments of device  10  that utilize a radiation source  14  that generates an axis-symmetric beam, such as a fiber laser, Vertical Cavity Surface Emitting Laser (VCSEL), LED, or lamp, for example. One or more axis-symmetric optical elements may also be used in certain embodiments of device  10  that utilize a radiation source  14  that generates an axis-asymmetric beam, such as a laser diode, for example. 
     Example Device Schematic 
       FIG. 4  illustrates a functional block diagram of an example device  10 , according to certain example embodiments. As shown, device  10  may include various components contained in a housing  24 , including a radiation source  14 , an optical system  15  including a beam scanning system  48 , a control system  18 , user interfaces  28  including displays  32 , a power source (in this example, a battery)  20 , various sensors  26 , and a cooling fan  34 . 
     Radiation source  14  includes a radiation source  14  (in this example, a laser diode) coupled to a heat sink  36 , and a fast axis optical element  64 . Optical system  15  may include upstream fast axis optical element  64 , a slow axis optical element  66 , and an optional downstream optical element  16 . In this example, fast axis optical element  64  (e.g., a rod lens) is mounted to the heat sink  36  of the radiation source  14 , and thus may be considered a component of radiation source  14 . Further, in this example slow axis optical element  66  is a multi-sector rotating scanning element  62  (e.g., element  100 A or  100 B) of a beam scanning system  48 . Thus, in this example, a rotating scanning element  62  acts as both a scanning element and a slow axis optical element. Beam scanning system  48  includes a motor  120  configured to rotate scanning element  62  and an encoder  121 , e.g., an indicator wheel fixed to scanning element  62 . In operation, radiation source  14  emits a generated beam  108 , which is influenced by fast axis optical element  64  to provide an input beam  110  to scanning element  62 . The input beam  110  is scanned by the multi-sector rotating scanning element  62  to generate a successive array of offset output beams  112  (e.g., angularly offset from each other). The output beams  112  are delivered through a downstream optic  16  (e.g., a fast axis rod lens), which further influences the beams, or a protective output window  44  that does not influence the beams, and to the skin  40  as delivered beams  114  to generate an array of treatment spots on the skin. 
     Device  10  may include one or more displacement sensors  200 , skin contact sensors  204 , and/or eye safety sensors  214  (and/or any other type or types of sensors  26  discussed herein). Displacement sensor  200  may monitor the lateral displacement of device  10  relative to the skin, e.g., as device  10  is moved across the skin in a gliding mode or stamping mode of operation. Skin contact sensors  204  may determine whether device  10 , in particular an application end  42 , is in contact with or sufficiently close to the skin for providing treatment to the user. Eye safety sensor  214  may determine whether the application end  42  of device  10  (e.g., an optical element  16  or window  44  at the application end  42 ), is positioned over the skin or the eye, such that device  10  can be controlled (e.g., radiation source  14  turned off) when the eye is detected, in order to prevent unintended exposure of the eye. 
     As discussed above, control system  18  may include any suitable subsystems for controlling the various components and aspects of device  10 . In this example, control system  18  includes a radiation source control system  128 , a scanning control system  130 , a displacement-based control system  132 , a usability control system  133 , a user interface control system  134 , a temperature control system  136 , a battery/charger control system  138 , and/or a motor/pulse control system  139 . Each control subsystem  128 - 139  may utilize or interact with control electronics  30 , sensors  26 , and user interfaces  28 , as appropriate. 
     Radiation source control system  128  may monitor and control various aspects of radiation source  14 . For example, system  128  may turn radiation source  14  on and off, and monitor and control the intensity of generated beam (e.g., by controlling the current to radiation source  14 ). As another example, in embodiments or configurations in which radiation source  14  is pulsed, system  128  may monitor and/or control the pulse duration, pulse on time, pulse off time, trigger delay time, duty cycle, pulse profile, or any other parameters of generated pulses from radiation source  14 . As another example, system  128  may monitor the temperature of radiation source  14 , which data may be used by temperature control system  136 , e.g., for controlling the pulse duration, the motor speed of motor  120 , the operation of cooling fan  34 , etc. In addition, system  128  may turn radiation source  14  off, or reduce power to radiation source  14  based on the monitored temperature of radiation source  14  (e.g., to prevent overheating). Radiation source control system  128  may utilize data or signals from any other control subsystems (e.g., scanning control system  130 , user interface control system  134 , temperature control system  136 , battery/charger control system  138 , and/or motor/pulse control system  139 ) for controlling aspects of radiation source  14 . 
     Scanning control system  130  may monitor and control various aspects of laser scanning system  48 , e.g., motor  120  which is configured to rotate a multi-sector scanning element  62  in certain embodiments. For example, system  130  may turn motor  120  on and off, and monitor and control the rotational speed, direction of rotation, and/or other parameters of motor  120 . Scanning control system  130  may communicate data or signals with, or otherwise cooperate with, other control subsystems, e.g., radiation source control system  128 , displacement-based control system  132 , usability control system  133 , user interface control system  134 , and/or motor/pulse control system  139 . 
     User interface control system  134  may include a user interface sensor control system  140  for monitoring and controlling displacement sensor  200 , skin contact sensors  204 , eye safety sensor  214 , and/or other sensors  26 . For example, system  134  may receive signals detected by each sensor, and send control signals to each sensor. User interface control system  134  may include a user input/display/feedback control system  142  for monitoring and controlling user interfaces  28  and displays  32 . For example, system  134  may receive user input data from various user interfaces  28 , and control information communicated to the user via displays  32  (e.g., visually, audibly, tangibly (e.g., by vibration), palpably, etc.). Scanning control system  130  may communicate data or signals with, or otherwise cooperate with, other control subsystems, e.g., radiation source control system  128 , scanning control system  130 , displacement-based control system  132 , usability control system  133 , temperature control system  136 , battery/charger control system  138 , and/or motor/pulse control system  139 . 
     Temperature control system  136  may be configured to monitor and control the temperature of one or more components of device  10 , e.g., radiation source  14 , motor  120  of scanning system  48 , battery  20 , etc. Thus, temperature control system  136  may receive data from one or more temperature sensors  208 , and control one or more fans  34  based on such data. In addition to controlling fan(s)  34 , temperature control system  136  may generate control signals for controlling radiation source  14 , motor  120 , etc. based on temperature data. For example, temperature control system  136  may communicate signals to radiation source control system  128  and/or scanning system control system  130  to control the operation of radiation source  14  and/or motor  120  based on detected temperature signals, e.g., to dynamically compensate for changes in the radiated wavelength associated with changes in the laser temperature, e.g., as discussed below with reference to  FIG. 63 . As another example, temperature control system  136  may communicate signals to radiation source control system  128  and/or scanning system control system  130  to turn off or otherwise control radiation source  14  and/or motor  120  to avoid overheating (or in response to a detected overheating) of such component(s), to maintain such components within predefined performance parameters, or for any other purpose. Temperature control system  136  may communicate data or signals with, or otherwise cooperate with, radiation source control system  128 , scanning control system  130 , user interface control system  134 , battery/charger control system  138 , and/or motor/pulse control system  139 . 
     Battery/charger control system  138  may be configured to monitor and control the charging of battery  20 . In some embodiments, multiple batteries  20  are included in device  10 . In some embodiments, battery  20  may be removable from device  10 , e.g., for replacement. As shown in  FIG. 3 , device  10  may be configured for connection to a wall plug-in charger  720  and/or a charging stand  730  via control electronics  30 , for charging battery  20 . System  138  may monitor the current charge and/or temperature of battery  20 , and regulate the charging of battery  20  accordingly. Battery/charger control system  138  may communicate data or signals with, or otherwise cooperate with, other control subsystems, e.g., user interface control system  134 , and/or temperature control system  136 . 
     Motor/pulse control system  139  may monitor and control various aspects of radiation source  14  and/or scanning system  48 , and may incorporate or combine various aspects of other subsystems discussed above, including aspects of radiation source control system  128 , scanning system control system  130 , displacement-based control system  132 , usability control system  133 , user interface control system  134 , and temperature control system  136 . For example, motor/pulse control system  139  may turn radiation source  14  on and off, control the pulse duration, pulse on time, pulse off time, trigger delay time, duty cycle, pulse profile, or any other parameters of generated pulses from radiation source  14  (e.g., by controlling the current to radiation source  14 ), control a motor  120  of scanning system  48  (e.g., to control the speed, position, etc. of a rotating beam-scanning element  100 ), etc. Motor/pulse control system  139  may control such parameters based on signals from various sensors  26  and/or by monitoring the rotation and/or position of an encoder  121 , which may be arranged to indicate the rotation and/or position of a rotating beam-scanning element  100 ). Motor/pulse control system  139  may utilize data or signals from any other control subsystems  128 - 138  for controlling aspects of radiation source  14  and/or scanning system  48 . Example aspects of motor/pulse control system  139  are discussed in greater detail below with reference to  FIGS. 55-59 . 
     Device  10  may include a delivery end, referred to herein as application end  42 , configured to be placed against the skin  40 . Application end  42  may include or house various user interfaces, including the treatment delivery interface for delivering output beams  112  to the user, as well as one or more sensors for detecting various characteristics of the target surface and/or treatment delivered by device  10 . For example, in the illustrated embodiment, application end  42  provides an interface for one or more displacement sensors  200 , skin contact sensors  204 , and/or eye safety sensors  214 , allowing these sensors to interface with the skin  40 . As shown in  FIG. 4 , some sensors  26  (e.g., radiation reflection-based displacement sensors  200  and/or eye safety sensors  214 ) may interface with the skin  40  via an optical element  16  or window  44  provided at the application end  42 , while other sensors  26  (e.g., capacitance-based contact sensors  204 ) may interface directly with the skin  40 . 
     General Operation of Scanning System 
       FIG. 5A  illustrates an example pattern or array of treatment spots  70 —in this example, a row  72  of treatment spots  70 —delivered by one full scan of an input beam  110  by scanning system  48 , with device  10  held stationary on the skin. For example, one full scan of an input beam  110  by scanning system  48  may be correspond to one full rotation of a multi-sector rotating scanning element, e.g., scanning element  100 A,  100 B, or  100 C discussed below. In this example, scanning system  48  delivers 12 output beams  112  to create 12 treatment spots  70  on the skin during a single scan of the input beam  110 . Thus, in such embodiment, scanning system  48  may utilize a 12-sector rotating scanning element. 
     As discussed above, in some embodiments or settings, device  10  may be operated in a “gliding mode” in which the device is manually moved, or glided, across the skin while delivering scanned radiation to the skin. Scanning system  48  may repeatedly scan rows  72  of treatment spots  70  onto the target area  40  as device  10  is glided across the skin, thus producing a two-dimensional array of treatment spots on the skin  40 . 
     In other embodiments, device  10  is configured to be used in a “stamping mode” in which device  10  is held relatively stationary at different locations on the skin, with one or more scanned rows or arrays of treatment spots  70  (overlapping or not overlapping) delivered at each location of device  10  on the skin. Thus, device  10  may be positioned at a first location on the skin, at which point one or more scanned rows or arrays of treatment spots  70  may then be delivered to the skin while device  10  is held relatively stationary, after which device  10  may then be moved—by lifting device  10  and repositioning it or by gliding device  10  across the surface of the skin—to a new location, at which point one or more scanned rows or arrays of treatment spots may then be delivered at this new location, and so on, in order to cover an area of the skin  40  as desired. In still another embodiment, beam scanning system  48  is configured to provide a generally two-dimensional array of treatment spots  70  in a single scan of input beam  110  (or multiple input beams  110 ), even assuming device  10  is held stationary on the skin. For example, the scanning system  48  may include a first rotating element that scans the beam(s) in one direction and a second rotating element that scans the beam(s) in the orthogonal direction. As another example, a single rotating element can be can be configured to provide multiple scanned rows of output beams, or a two-dimensional array of output beams, during a single scan, as discussed below. 
     In other embodiments, device  10  may be configured for use in both a “gliding mode” and “stamping mode,” as selected by the user. 
       FIG. 5B  illustrates an example array of treatment spots generated by an example device  10  used in a gliding mode. In particular, the figure shows three scanned rows  72  of treatment spots  70 , indicated as rows  72 A,  72 B, and  72 C, aligned relative to each other in the glide direction, which forms a two-dimensional array  71  of treatment spots  70 . Each row  72  extends generally diagonally with respect to the scan direction due to the movement of device  10  in the glide direction during the successive delivery of individual treatment spots  70  in each row  72 . 
     The degree to which each row  72  is aligned diagonally with respect to the scan direction, which may influence the spacing of adjacent treatment spots aligned in the glide direction (e.g., treatment spots  70 A and  70 B), may depend on one or more various factors, e.g., (a) the manual glide speed (the speed at which device  10  is glided across the skin), (b) the scanning rate (e.g., the rate at which treatment spots are successively delivered to the skin and the time between scans, (c) any displacement-based control, which may enforce a predetermined minimum spacing between adjacent rows in the glide direction, e.g., by interrupting the delivery of radiation to ensure the predetermined minimum spacing, and/or (d) any other relevant factor. In some embodiments, the scanning rate or particular aspects of the scanning rate (e.g., pulse on time, pulse off time, pulse frequency, etc.), and/or the predetermined minimum spacing between rows as controlled by a displacement-based control system, may be selectable or adjustable automatically by control system  18 , manually by a user, or both. 
     Further, the distance between adjacent treatment spots  70  in the scan direction (e.g., treatment spots  70 C and  70 D) may depend on one or more various factors, e.g., the scanning rate, the distance between the center points of adjacent treatment spots, the size and shape of individual treatment spots, etc., which factors may be defined by the configuration of the beam scanning optics  62 , other optics  16  or aspects of optical system  15 , or other factors. In some embodiments, one or more of these factors may be selectable or adjustable automatically by control system  18 , manually by a user, or both. In some embodiments or device settings, adjacent treatment spots in the scan direction are spaced apart from each other by areas of non-irradiated skin, thus providing a fractional treatment. In some embodiments or device settings, adjacent treatment spots in the scan direction may abut each other edge-to-edge, or may overlap each other, in order to provide contiguous rows of irradiated areas. Such contiguous rows may be spaced apart from each other in the glide direction, may abut each other edge-to-edge, or may overlap each other to provide a fully covered (i.e., non-fractional) irradiated area, as defined by a variety of factors such as those discussed above, which may or may not be manually and/or automatically selectable or adjustable. 
     Thus, it should be clear that the fractional pattern of treatment spots shown in  FIG. 5B , in which treatment spots are spaced apart from each other in both the glide direction and scan direction, is merely one example pattern. Device  10 , and in particular optical system  15  (including scanning system  48 ), may be configured for providing various different treatment spot patterns, e.g., as discussed above, and as shown in the example of  FIGS. 21-25 , which are discussed below in more detail. 
     Beam scanning system  48  may include any suitable beam scanning optics  62  and other component for scanning an individual radiation beam into a sequentially-delivered array of beams to form a pattern of treatment spots in the skin  40 . For example, as discussed below with respect to  FIGS. 6-20 , scanning system  48  may include a rotating beam scanning element having a number of deflection sectors that successively deflect (e.g., reflect or transmit with a deflection) a single input beam  110  to provide an array of successively delivered output beams  112 , which may be offset from each other (e.g., angularly offset, translationally offset, or both). This process of using a scanning element to successively deflect an input beam  110  to provide an array of successively delivered output beams  112  (which are offset from each other in some aspect) is referred to as “scanning” the input beam  110 . 
     In some embodiments, the rotating multi-sector scanning element may be generally disc-shaped (e.g., as shown in  FIGS. 7A-7C ) or generally cup-shaped (e.g., as shown in  FIGS. 8A-8E ). The multiple deflection sectors may be arranged around a circumference of the scanning element and may be configured to successively deflect the incident input beam  110  by different angles to provide a successive array of deflected output beams  112  that are angularly offset from each other. The angularly offset array of output beams  112  may be delivered directly to the skin  40 , or may be influenced by further optics  16  before being delivered to the skin  40  as delivered beams  114 . For example, optics  16  may be provided to parallelize the array of output beams  112 , or to influence the divergence or convergence of individual output beams  112 , before being delivered to the target area  40  as delivered beams  114 . 
     As another example, as discussed below with respect to  FIGS. 12-20 , beam scanning system  48  may include a generally stair-stepped rotating scanning element with a number of reflection sectors that successively reflect an incident input  110  beam to provide an array of successive output beams  112  that are translationally and/or angularly offset from each other. In some embodiments, the reflection sectors of the scanning element include planar reflection surfaces that are offset from each other in order to provide a successive array of reflected output beams  112  that are translationally offset from each other and either parallel to each other or angularly offset from each other. The translationally (and/or angularly) offset array of reflected output beams  112  may be delivered directly to the skin  40 , or may be influenced by further optics  16  before being delivered to the skin  40  as delivered beams  114 . For example, optics  16  may be provided to parallelize the array of output beams  112 , or to influence the divergence or convergence of individual output beams  112 , before being delivered to the target area  40  as delivered beams  114 . 
     Scanning System May Include a Rotating Multi-Sector Scanning Element 
       FIGS. 6-20  illustrate various aspects and embodiments of a rotating multi-sector beam scanning element  100  for use in certain embodiments of scanning system  48 . More particularly,  FIGS. 6A-6C  illustrate the general structure and operation of a rotating multi-sector scanning element  100  for scanning an input beam  110 , while  FIGS. 7-20  are directed to three example types of rotating multi-sector scanning elements  100  for use in scanning system  48 : an example disc-shaped multi-sector transmissive scanning element  100 A; an example cup-shaped multi-sector transmissive scanning element  100 B; and an example stair-stepped reflective scanning element  100 C. 
       FIG. 6A  illustrates a basic structure of a rotating element  100 , according to some embodiments. Element  100  has a body  102  configured to rotate about an axis A. Body  102  includes a plurality of sectors  104  generally arranged around the circumference or periphery of the body  12  and configured to deflect and/or otherwise optically influence an input beam  110  into an array of output beams  112  offset from each other. Depending on the particular embodiment, each sector  104  may transmit but deflect and/or otherwise optically influence the input beam  110 , as indicated by example arrow  112 A (e.g., where element  100  is a disc-shaped transmissive element  100 A or cup-shaped transmissive element  100 B, as discussed below) or reflect and/or otherwise optically influence the input beam  110 , as indicated by example arrow  112 B (e.g., where element  100  is a stair-stepped reflective element  100 C, as discussed below). In some embodiments, as each individual sector  104  rotates through the input beam  110 , the angular deflection of the corresponding output beam  112  may remain constant or substantially constant so that each output beam  112  is stationary or substantially stationary with respect to device  10  for the duration of that output beam  112 . Such sectors are referred to herein as “constant angular deflection” sectors. Alternatively, the deflection of each output beam  112  may vary during the rotation of the corresponding sector  104  through the input beam  110  so that each output beam  112  traces a pattern, e.g., a line or arc. 
     As shown in  FIG. 6A , sectors  104   1 - 104   n  arranged circumferentially around axis A are configured to deflect (reflect or transmissively deflect) an input beam  110  to produce an array of offset output beams  112 . Thus, as the rotating element  100  rotates through the input beam  110  for one full revolution (i.e., one full scan of input beam  110 ), sectors  104   1 - 104   n  produce a successively scanned array of n output beams  112 , each offset from one, some, or all other output beams  112  in the scanned array, to provide a scanned row or array of treatment spots  70  on the skin  40 . 
     As used herein, unless otherwise specified, an “array” means any pattern of elements (e.g., output beams  112  or treatment spots  70 ) arranged in any manner, e.g., in a linear row, a non-linear row, a regular two-dimensional pattern, an irregular two-dimensional pattern, or any other pattern. 
     Further, as used herein, unless otherwise specified, “offset” means angularly offset (e.g., diverging or converging lines), translationally offset (e.g., offset parallel lines), or both angularly and translationally offset. Thus, output beams  112  that are “offset” from each other may be angularly offset (e.g., output beams  112  generated by transmissive sectors  104 A and  104 B of certain embodiments of elements  110 A and  100 B, respectively), translationally offset (e.g., output beams  112  generated by reflective sectors  104 C of certain embodiments of stair-stepped element  110 C), or both angularly and translationally offset (e.g., output beams  112  generated by reflective sectors  104 C of certain other embodiments of stair-stepped element  110 C). 
       FIG. 6B  illustrates an example pattern of treatment spots delivered by one rotation of element  100  (i.e., one scan of input beam  110 ), assuming device  10  is held stationary with respect to the target area, for the purpose of illustration. The treatment spots are labeled 1 through 12, indicating the sequential order in which each treatment spot is produced, beginning with treatment spot  1  produced by sector  104   1 , followed by treatment spot  2  produced by sector  104   2 , and so on. In this example, each sector  104  has been configured to provide a constant deflection as that sector rotates through the input beam  110 , such that each sector  104  produces a stationary or substantially stationary spot  70  on the skin. 
     Sectors  104   1  to  104   n  may be configured such that the array of treatment spots  70  may be delivered in any desired sequential order, e.g., in terms of a particular direction of the array. For example, in the example shown in  FIG. 6B , sectors  104   1  through  104   12  are configured to produce treatment spots  1 - 12  in sequential order along the scan direction. However, treatment spots may be delivered in any other sequential order, based on the particular design and configuration of element  100 , e.g., as discussed below with reference to  FIGS. 22-25 . 
       FIG. 6C  illustrates an example pattern of treatment spots delivered by one rotation of element  100  (i.e., one scan of input beam  110 ), assuming device  10  is glided over the target area in a direction substantially perpendicular to the scan direction (e.g., device  10  operating in a gliding mode, as discussed above). As with the example shown in  FIG. 6B , in the example shown in  FIG. 6C , sectors  104   1  to  104   n  are configured to deliver a pattern of treatment spots in sequential order along the scan direction. This configuration of element  100  produces a generally linear row of treatment spots aligned diagonally with respect to the scan direction, due to the movement of the device  10  in the glide direction. Again, it should be understood that treatment spots may be delivered in any other sequential order, based on the particular design and configuration of element  100 , which may provide a variety of different two-dimensional treatment spot patterns as device is glided across the skin  40 , as discussed in greater detail below. 
     Disc-Shaped Rotating Scanning Element 
       FIGS. 7A-7C  illustrate an example embodiment of a rotating disc-shaped, multi-sector beam scanning element  100 A for use in certain embodiments of beam scanning system  48 . In particular,  FIG. 7A  is an isometric front (i.e., upstream) view of disc-shaped element  100 A;  FIG. 7B  is an isometric rear (i.e., downstream) view of disc-shaped element  100 A; and  FIG. 7C  is a side view of disc-shaped element  100 A. 
     As shown, disc-shaped element  100 A has a body  102 A configured to rotate about axis A (e.g., driven by a motor  120 ). In this example, body  102 A includes 12 sectors  104 A 1  to  104 A 12  arranged circumferentially around axis A. Each sector  104 A 1  to  104 A 12  comprises a transmissive lenslet configured to (a) deflect an input beam  110  in a different angular direction, and (b) focus (i.e., influence the divergence/convergence of) the input beam  110  in at least one axis (e.g., the fast axis, the slow axis, or both). As element  100 A rotates one full revolution through the input beam  110  (i.e., one full scan), lenslets  104 A 1  to  104 A 12  produce a successively scanned array of 12 output beams  112  that are angularly offset from each other, to provide a scanned array of 12 treatment spots on the skin  40 . 
     In some embodiments, each transmissive lenslet  104 A 1  to  104 A 12  is configured to (a) deflect the input beam  110  in a different angular direction, such that the output beams  112  are offset from each other along one axis (e.g., the slow axis or the fast axis), and (b) focus the input beam  110  along that same axis (e.g., the slow axis or the fast axis), while not substantially affecting the beam along the orthogonal axis (e.g., the other of the slow axis and fast axis). For example, in an example embodiment, each transmissive lenslet is configured to (a) deflect the input beam  110  in a different angular direction such that the output beams  112  are offset from each other in the slow axis direction, and (b) focus the slow axis profile of the beam, while not substantially affecting the fast axis profile of the beam. Thus, in such example embodiment, scanning element  100 A acts as both a beam scanning element  62  and a slow axis element  66 , e.g., as discussed above with reference to  FIGS. 3C and 3D . 
     As discussed above, lenslets  104 A may be configured such that the array of treatment spots may be generated in any desired sequential order, e.g., in terms of one or more particular directions. In this example embodiment, lenslets  104 A 1  to  104 A 12  are configured such that the 12 corresponding treatment spots are delivered along a linear scan direction in a pseudo-random order, e.g., as discussed below with reference to  FIG. 22C . 
     In the example illustrated embodiment, each lenslet  104 A has a toroid shape defined by rotating a cross-sectional shape around the rotational axis A of element  100 A. The rotated cross-sectional shape may be defined by a pair of opposing edges that form the opposing surfaces of the lenslet upon rotation of the cross-sectional shape. The pair of opposing edges may have any suitable shapes. For example, the pair of opposing arcs may be a pair of opposing arcs (with each arc being circular or non-circular, and with the opposing arcs being symmetrical or non-symmetrical with respect to each other), an arc and an opposing non-arc (e.g., a linear segment or other shape), or any other suitable shapes for forming the desired surfaces of the lenslet upon rotation of the cross-sectional shape. A geometric “centerline” of the cross-sectional shape of each lenslet may be defined between the pair of opposing edges. Further, each toroidal lenslet may define a “lenslet apex,” defined herein as the thickest portion of the lenslet, in the direction from edge-to-edge of the cross-sectional shape. 
     In some embodiments, each lenslet has a toroid shape defined by rotating a cross-sectional shape around the rotational axis A, wherein the cross-sectional shape is defined by a pair of opposing arcs. In other embodiments, each lenslet has a toroid shape defined by rotating a cross-sectional shape around the rotational axis A of element  100 A, wherein the cross-sectional shape is defined by an arc opposed by a linear segment. 
     Thus, while the input beam  110  is incident on any particular lenslet  104 A, it is affected in a manner similar to the shifted lens shown in  FIGS. 9A-9B  (discussed below). The different shapes of lenslets  104 A 1  to  104 A 12  of element  100 A are generated in effect by varying the radial distance from input beam  110  to the lenslet apex, thus presenting the incoming laser beam  110  with a different relative position between the beam center and lenslet apex. This difference in relative positioning results in each output beam  112  being deflected by a different angular amount for each sector. In this example, the angular deflection of each output beam  112  with respect to device  10  is constant as each respective lenslet  104  rotates through input beam  110 , such that output spots (rather than lines, arcs, or other shapes) are produced from each sector. Thus, each output beam  112  may be referred to as a “constant angular deflection” output beam  112 . As discussed above, in addition to deflecting the input beam  110 , each lenslet also focuses the input beam  112 , e.g., in the slow-axis direction, to provide a desired focal plane and/or a desired beam profile at the skin  40 . 
     Further, in this example embodiment, along a front or rear view of element  100 A, each lenslet  104 A is essentially a circular sector sweeping the same circumferential or central angle (30 degrees in this example). Thus, with reference to  FIG. 7A , for each lenslet, θ=30 degrees. In other embodiments of disc-shaped element  100 A, different lenslets may be circular sectors that sweep different central angles. In other embodiments of disc-shaped element  100 A, the lenslets may have any other suitable shapes (i.e., other than circular sectors) in the front or rear view of element  100 A, and the different lenslets may sweep the same or different circumferential or central angles. 
     Further, although the example disc-shaped element  100 A shown in  FIGS. 7A-7C  includes 12 lenslets, in other embodiments disc-shaped element  100 A may include any other number of lenslets, more than or fewer than 12. 
     Cup-Shaped Rotating Scanning Element 
       FIGS. 8A-8E  illustrate various aspects and embodiments of a rotating cup-shaped, multi-sector beam scanning element  100 B for use in certain embodiments of scanning system  48 . In particular,  FIG. 8A  is an isometric front (i.e., upstream) view of cup-shaped element  100 B;  FIG. 8B  is an isometric rear (i.e., downstream) view of cup-shaped element  100 B;  FIG. 8C  is a side view of cup-shaped element  100 B;  FIG. 8D  is a front view of cup-shaped element  100 B; and  FIG. 8E  is a rear view of cup-shaped element  100 B. 
     Cup-shaped rotating element  100 B is similar to disc-shaped rotating element  100 A with each lenslet “tilted” toward the axis of rotation in the upstream direction to form a cup shape lens element. Cup-shaped element  100 B operates according to the same basic principle as disc-shaped element  100 A discussed above, with each lenslet (a) deflecting deflect an input beam  110  in a different angular direction, and (b) focusing the input beam  110  along at least one axis (e.g., the fast axis, the slow axis, or both) to generate a sequential series of output beams  112  propagating to achieve a desired pattern of treatment spots on the skin  40 . As with other embodiments discussed herein, cup-shaped element  100 B can be configured such that the angular deflection produced by each lenslet  104  either (a) remains constant as that lenslet  104  rotates through the input beam  110  (e.g., to produce a spot on the skin) or (b) varies as the lenslet  104  rotates through the input beam  110  (e.g., to produce a line segment or arc on the skin). 
     As shown in  FIGS. 8A-8E , cup-shaped element  100 B has a body  102 B configured to rotate about axis A (e.g., driven by a motor  120 ). In this example, body  102 B includes 12 sectors  104 B 1  to  104 B 12  arranged circumferentially around axis A. Each sector  104 B 1  to  104 B 12  comprises a transmissive lenslet configured to (a) deflect an input beam  110  in a different angular direction, and (b) focus (i.e., influence the divergence/convergence of) the input beam  110  in at least one axis (e.g., the fast axis, the slow axis, or both). As element  100 B rotates one full revolution through the input beam  110  (i.e., one full scan), lenslets  104 B 1  to  104 B 12  produce a successively scanned array of 12 output beams  112  that are angularly offset from each other, to provide a scanned array of 12 treatment spots on the skin  40 . 
     In some embodiments, each transmissive lenslet  104 B 1  to  104 B 12  is configured to (a) deflect the input beam  110  in a different angular direction, such that the output beams  112  are offset from each other along one axis (e.g., the slow axis or the fast axis), and (b) focus the input beam  110  along that same axis (e.g., the slow axis or the fast axis), while not substantially affecting the beam along the orthogonal axis (e.g., the other of the slow axis and fast axis). For example, in an example embodiment, each transmissive lenslet is configured to (a) deflect the input beam  110  in a different angular direction such that the output beams  112  are offset from each other in the slow axis direction, and (b) focus the slow axis profile of the beam, while not substantially affecting the fast axis profile of the beam. Thus, in such example embodiment, scanning element  100 B acts as both a beam scanning element  62  and a slow axis element  66 , e.g., as discussed above with reference to  FIGS. 3C and 3D . 
     As discussed above, lenslets  104   b  may be configured such that the array of treatment spots may be generated in any desired sequential order, e.g., in terms of one or more particular directions. In this example embodiment, lenslets  104 B 1  to  104 B 12  are configured such that the 12 corresponding treatment spots are delivered along a linear scan direction in a pseudo-random order, e.g., as discussed below with reference to  FIG. 22C . 
     As with lenslets  104 A of example disc-shaped element  100 A, each lenslet  104 B of example cup-shaped element  100 B may have a toroid shape defined by rotating a cross-sectional shape around the rotational axis A of element  100 B. The rotated cross-sectional shape may be defined by a pair of opposing edges that form the opposing surfaces of the lenslet upon rotation of the cross-sectional shape. The pair of opposing edges may have any suitable shapes. For example, the pair of opposing arcs may be a pair of opposing arcs (with each arc being circular or non-circular, and with the opposing arcs being symmetrical or non-symmetrical with respect to each other), an arc and an opposing non-arc (e.g., a linear segment or other shape), or any other suitable shapes for forming the desired surfaces of the lenslet upon rotation of the cross-sectional shape. A geometric “centerline” of the cross-sectional shape of each lenslet may be defined between the pair of opposing edges. Further, each toroidal lenslet may define a “lenslet apex,” defined herein as the thickest portion of the lenslet, in the direction from edge-to-edge of the cross-sectional shape. 
     In some embodiments, each lenslet has a toroid shape defined by rotating a cross-sectional shape around the rotational axis A, wherein the cross-sectional shape is defined by a pair of opposing arcs. In other embodiments, each lenslet has a toroid shape defined by rotating a cross-sectional shape around the rotational axis A of element  100 B, wherein the cross-sectional shape is defined by an arc opposed by a linear segment. 
     In some embodiments, e.g., the example embodiment shown in  FIGS. 8A-8E , each lenslet  104 B of cup-shaped element  100 B has a respective cross-section defined by a pair of circular arcs centered around a tilted centerline A′. (The pair of arc and centerline for each lenslet are also discussed below with respect to  FIG. 9B ). Each centerline is “tilted” in that it is angularly offset from the rotational axis A of element  100 B by a defined angle α (i.e., the angle at which each lenslet  104 B of element  100 B is “tilted” toward rotational axis A as compared to the lenslets  104 A of disc-shaped element  100 A). The toroid shape of each lenslet  104 B of cup-shaped element  100 B is defined by rotating the respective cross-section (i.e., pair of opposing arcs centered around a tilted centerline) around the rotational axis A of element  100 B. 
       FIG. 8A  illustrates (a) a tilted centerline A′ 5  corresponding to lenslet  104 B 5  and angularly offset from rotational axis A by an angle α 5 , and (b) a tilted centerline A′ 6  corresponding to lenslet  104 B 6  and angularly offset from rotational axis A by an angle α 6 . Thus, lenslet  104 B 5  has a toroid shape defined by rotating around rotational axis A a cross-section defined by a pair of circular arcs centered around tilted centerline A′ 5 , while lenslet  104 B 6  has a toroid shape defined by rotating around rotational axis A a cross-section defined by a pair of circular arcs centered around tilted centerline A′ 6 . The different shapes of lenslets  104 B 1  to  104 B 12  of element  100 B are generated by varying a “radial” distance—specifically, along each respective tilted centerline—of the lenslet apex (i.e., the thickest part of the lenslet cross-section), as described in greater detail below with respect to  FIG. 9B , thus presenting the incoming beam  110  with a different relative position between the beam center and the lenslet apex, for different lenslets. This difference in relative positioning results in each output beam  112  being deflected by a different angular amount, as discussed below with respect to  FIG. 9B . 
     In some embodiments, cup-shaped scanning element  100 B is configured such that the toroidal shape of each lenslet  104 B provides a “constant angular deflection” output beam  112 , as that lenslet  104 B sweeps across the input beam  110 . 
     In this embodiment, each tilted centerline A′ 1  through A′ 12  is angularly offset from rotational axis A by the same angle α (thus, for A′ 5  and A′ 6  discussed above, α 5 =α 6 ). In other words, each lenslet  104 B is tilted by the same degree. In some embodiments, α is less than 80 degrees. In certain embodiments, α is between about 30 degrees and about 60 degrees. In particular embodiments, α is about 47 degrees. In other embodiments, different tilted centerline A′ 1  through A′ 12  may be angularly offset from rotational axis A by different angles (e.g., α 5 ≠α 6 ). In other words, each lenslet  104 B may be tilted by different degrees. 
       FIGS. 8D and 8E  illustrate the front and rear views, respectively, of cup-shaped element  100 B. From these perspectives, each lenslet  104 B is essentially a circular sector sweeping the same circumferential or central angle (30 degrees). Thus, with reference to  FIG. 8D , for each lenslet, θ=30 degrees. In other embodiments of cup-shaped element  100 B, different lenslets  104 B may be aspherical sectors that sweep different central angles. In other embodiments of cup-shaped element  100 B, the lenslets may have any other suitable shapes (i.e., other than aspherical sectors) in the front or rear view of element  100 B, and the different lenslets may sweep the same or different circumferential or central angles. 
     Further, although the example cup-shaped element  100 B shown in  FIGS. 8A-8E  includes 12 lenslets, in other embodiments cup-shaped element  100 B may include any other number of lenslets, more than or fewer than 12. 
     The basic illustrative theory behind the multi-lenslet elements  100 A and  100 B and how they deflect a radiation beam is shown in  FIGS. 9A-9B . With reference to the orientation shown in  FIG. 9A , the radiation beam B enters from the left and passes undeviated through the center of the lens at the left. When the lens is shifted up (off axis relative to the beam, as indicated by the vertical arrow) as shown on the right, the beam is deviated by an angle generally proportional to the shift. 
     Lenslets  104  may have any suitable shape or configuration to affect the beam. For example, as discussed below in greater detail, lenslets  104  may have a toroidal shape, a circular shape, an aspheric shape, or any other suitable shape or configuration. 
       FIG. 9B  illustrates a representation of a beam scanning element  100  (e.g., element  100 A or  100 B) according to an example embodiment. Element  100  includes a plurality of lenslets  104  arranged around a rotational axis A. In this example, each the lenslet  104  has a toroidal shape defined by rotating a pair of arcs AP around rotational axis A, where the rotation of the arc pair AP in each sector  104  is indicated by the dashed line sweeping through each sector  104  (such that each dashed line is an arc centered on the rotational axis A). Here, each arc pair AP is shown orthogonal to its actual orientation, for the purposes of illustration. Arc pairs AP may comprise circular arcs or non-circular arcs. In some embodiments (e.g., disk-shaped scanning element  100 A), the centerline C of each lenslet  104  resides in the same plane, specifically the plane of rotation of element  100  (i.e., 90 degrees from the axis of rotation A). In other embodiments (e.g., cup-shaped scanning element  100 B), each lenslet  104  is tilted with respect to plane of rotation such that the centerline C of each lenslet  104  extends at an angle between plane of rotation of element  100  and the axis of rotation A). This angle of tilt may be the same for each lenslet  104  or may be different for different lenslets  104 , e.g., as discussed above regarding cup-shaped scanning element  100 B. 
     As shown, the lens apex (i.e., the thickest point) of each lenslet  104  sweeps through the dashed line in each sector  104 . For each lenslet  104 , the distance D of the lens apex from rotational axis A is different than some or all other lenslets  104 . This difference in distance D among the different lenslets  104  provides the different angular deflections of output beam  112  produced by the respective lenslets  104 . 
     The toroidal lenslets  104  as discussed above provide for constant angular deflection of the output beam  112  produced by each lenslet  104 , as that lenslet  104  sweeps across the input beam  110 . 
     In some embodiments, each lenslet  104  may have the same optical power, or substantially the same optical power. In other embodiments, lenslets  104  may have slightly different optical powers, in order to (a) provide a uniform focal plane for the array of output beams  112  with respect to the skin surface (e.g., the optical powers or individual lenslets  104  may be selected to compensate for the different angular deflection of each output beam  112 ), and/or (b) provide for distortion correction among the various output beams  112 . In other embodiments, each lenslet  104  may have substantially different optical powers. 
     It should be understood that the specific shapes of lenslets  104  specifically shown and discussed herein are examples only, and that lenslets  104  may have any other shapes or configurations (which may or may not be toroid shaped) suitable for deflecting an input beam  110  in different angular directions. 
     Example Optics Systems Utilizing a Rotating Multi-Lenslet Scanning Element 
       FIGS. 10 and 11  illustrate example optical systems  15  that utilize a rotating multi-lenslet scanning element  100 , according to certain embodiments. 
       FIGS. 10A and 10B  illustrate top and side views, respectively, of an optical system  15 A that includes a rotating disc-shaped scanning element  100 A, e.g., as described above with respect to  FIGS. 7A-7C , according to certain embodiments. Optical system  15 A is configured to scan and deliver radiation generated by radiation source  14  to form a pattern of treatment spots  70  on the skin  40 . 
     In this example embodiment, the radiation source  14  is a laser diode that generates an axially-asymmetric beam  108  including a fast axis and an orthogonal slow axis. Optics  16  may include a fast axis optic  64 , and a disc-shaped scanning element  100 A rotated by a motor  120 . In some embodiments, optics  16  may also include a downstream fast axis optic  64 ′, whereas in other embodiments this optic is omitted. 
     As shown, laser  14  generates beam  108 , which diverges relatively rapidly in the fast axis (as shown in  FIG. 10B ) and diverges relatively slowly in the slow axis (as shown in  FIG. 10A ). Fast axis optic  64 , e.g., a rod lens, aspheric lens, or any other suitable optical element, is configured to convert the beam in the fast axis from rapidly diverging to less diverging (e.g., slowly diverging, collimated, or converging) toward target area  40 , as shown in  FIG. 10B . In some embodiments, fast axis lens  64  does not significantly influence the slow axis beam angular distribution profile (e.g., the convergence/divergence of the slow axis), as shown in  FIG. 10A . 
     Fast axis optic  64  delivers an input beam  110  to rotating disc-shaped scanning element  100 A, which includes multiple lenslets  104  that generate a successive series of output beam  112  toward the skin  40 , as shown in  FIG. 10A . In addition to deflecting the various output beams in the scan direction to form a desired pattern of treatment spots on the skin  40 , lenslets  104  of element  100 A also focus the beam in the slow axis, to convert the slow axis profile of the beam from slowly diverging to slowly converging (or in some embodiments, collimated). Thus, a single element  100 A operates as both the beam scanning element and the slow axis optic  66 , thus reducing or minimizing the number of separate components for such functions, which may be desirable. In some embodiments, lenslets  104  of element  100 A do not substantially influence the fast axis beam profile, as shown in  FIG. 10B . 
     Fast axis optic  64  and lenslets  104  of element  100 A may be configured to converge the beam in the fast and slow axes, respectively, such that each output beam  112  has a focal point or focal plane located at or slightly above the surface of the skin (i.e., outside the skin). As used herein, the “focal point” or “focal plane” of each delivered beam  114  is defined as the plane perpendicular to the propagation axis of the beam  114  having the minimum cross-sectional area. For embodiments that provide axially-asymmetric delivered beams  114  (e.g., embodiments that utilize an axially-asymmetric radiation source  14 , such as a laser diode), the minimum cross-sectional area is typically located between the waist of the fast axis beam profile and the waist of the slow axis beam profile. 
     Further, as discussed above, in some embodiments a downstream fast axis optic  64 ′ is provided for additional focusing and/or imaging and/or treatment of output beams  112  for delivery to the skin as delivered beams  114 . Other embodiments omit the downstream lens  64 ′, and thus include only a single fast axis optic (element  64 ) and a single slow axis optic (element  100 A). This design may thus reduce or minimize the number of optical elements as compared to existing systems or other embodiments, which may be desirable for various reasons. 
       FIGS. 11A and 11B  illustrate top and side views, respectively, of an optical system  15 B that includes a rotating cup-shaped scanning element  100 B, e.g., as described above with respect to  FIGS. 8A-8E , according to certain embodiments. Optical system  15 B is similar to optical system  15 A, except scanning system  48  includes a cup-shaped scanning element  100 B, rather than disc-shaped element  100 A. Again, it is assumed in this example that the treatment radiation source  14  is a laser diode that generates an axially-asymmetric beam  108  defining a fast axis and an orthogonal slow axis. As with the example discussed above, the downstream fast axis optic  64 ′ may be included or omitted, depending on the particular design. 
     As shown, laser  14  generates beam  108 , which diverges relatively rapidly in the fast axis (as shown in  FIG. 11B ) and diverges relatively slowly in the slow axis (as shown in  FIG. 11A ). Fast axis optic  64 , e.g., a rod lens, aspheric lens, or any other suitable optical element, is arranged to convert the beam in the fast axis from rapidly diverging to less diverging (e.g., slowly diverging, collimated, or converging) toward target area  40 , as shown in  FIG. 11B . In some embodiments, fast axis lens  64  does not significantly influence the slow axis beam angular distributi1n profile (e.g., the convergence/divergence of the slow axis), as shown in  FIG. 10A . 
     Fast axis optic  64  delivers an input beam  110  to rotating cup-shaped scanning element  100 B, which includes multiple lenslets  104  that generate a successive series of output beam  112  toward the skin  40 , as shown in  FIG. 11A . In addition to deflecting the various output beams in the scan direction to form a desired pattern of treatment spots in the target area  40 , lenslets  104  of element  100 A also focus the beam in the slow axis, to convert the slow axis profile of the beam from slowly diverging to slowly converging. (or in some embodiments, collimated). Thus, a single element  100 B operates as both the beam scanning element  62  and the slow axis optic  66 , thus reducing or minimizing the number of separate components for such functions, which may be desirable. In some embodiments, lenslets  104  of element  100 B do not substantially influence the fast axis beam profile, as shown in  FIG. 10B , as shown in  FIG. 11B . 
     Fast axis optic  64  and lenslets  104  of element  100 B may be configured to converge the beam in the fast and slow axes, respectively, such that each output beam  112  has a focal point or focal plane located at or slightly above the surface of the skin (i.e., outside the skin). 
     Further, as discussed above, in some embodiments a downstream fast axis optic  64 ′ is provided for additional focusing and/or imaging and/or treatment of output beams  112  for delivery to the skin as delivered beams  114 . Other embodiments omit the downstream lens  64 ′, and thus include only a single fast axis optic (element  64 ) and a single slow axis optic (element  100 B). This design may thus reduce or minimize the number of optical elements as compared to existing systems or other embodiments, which may be desirable for various reasons. 
     Cup-shaped scanning element  100 B is arranged such that the rotational axis A of element  100 B is aligned at an angle σ relative to a central axis of input beam  110 , indicated as axis X. In some embodiments, e.g., as shown in  FIG. 11A , angle σ is greater than zero, which may allow scanning system  48  to be arranged in housing  24  of device  10  such that one or more external dimensions of housing  24  may be reduced, e.g., as compared to a scanning system utilizing a disc-shaped scanning element, or certain known scanning systems. For example, angle σ may be greater than 10 degrees. In certain embodiments, angle σ is greater than 30 degrees. Further, angle σ may be greater than 45 degrees, which may allow for particular reduction of one or more external dimensions of housing  24 , or other component packaging advantages. In particular embodiments, angle σ is between 45 and 55 degrees. In one example embodiment, angle σ is about 47 degrees. 
     Further, angle σ may be related to the angle of forward tilt of each lenslet  104 , defined above as angle α with reference to  FIG. 8A . For example, σ+α may be in the range between 60 and 120 degrees. In some embodiments, σ+α may be in the range between 80 and 100 degrees. In particular embodiments, σ+α is equal to or approximately equal to 90 degrees (i.e., angles σ and α are complementary or approximately complementary angles). 
     Alternatively or in addition, rotational axis A of element  100 B may be aligned at an angle β relative to a scan direction, i.e., a direction of the beam deflection caused by lenslets  104 , indicated as direction Y. Scan direction Y may or may not be perpendicular to the central axis X of input beam  110 , depending the configuration of the particular embodiment. 
     In some embodiments, e.g., as shown in  FIG. 11A , angle β is less than 90 degrees, which may allow scanning system  48  to be arranged in housing  24  of device  10  such that one or more external dimensions of housing  24  may be reduced, e.g., as compared to a scanning system utilizing a disc-shaped scanning element, or certain known scanning systems. For example, angle β may be less than 80 degrees. In certain embodiments, angle β is less than 60 degrees. Further, angle β may be less than 45 degrees, which may allow for particular reduction of one or more external dimensions of housing  24 , or other component packaging advantages. In particular embodiments, angle β is between 35 and 45 degrees. In one example embodiment, angle β is about 43 degrees. 
     Further, angle β may be related to the angle of forward tilt of each lenslet  104 , defined above as angle α with reference to  FIG. 8A . For example, angles σ and β may differ by less than 30 degrees. In some embodiments, angles σ and β may differ by less than 10 degrees. In particular embodiments, angles σ and β are equal or approximately equal. 
     Stair-Stepped Rotating Scanning Element 
       FIGS. 12-20  illustrate various aspects and embodiments of a stair-stepped rotating beam scanning element  100 C and example scanning systems  48  including a stair-stepped scanning element  100 C. 
       FIG. 12  illustrates an example stair-stepped rotating element  100 C. Rotating element  100 C has a body  102 C configured to rotate about an axis A. Body  102 C defines a plurality of reflection sectors  104 C 1 - 104 C 4  arranged circumferentially around axis A, and respectively defining a plurality of reflection surfaces  106 C 1 - 106 C 4  arranged in a generally stair-stepped manner. Reflection surfaces  106 C 1 - 106 C 4  are configured to reflect an input beam  110  (received directly from radiation source  14  or from optics arranged upstream from rotating element  100 C or otherwise) such that the input beam  110  reflects off each reflection surface  106 C 1 - 106 C 4  in succession, one at a time, as the rotating element rotates about axis A, to generate a successive array of output beams  112 . 
     As shown, reflection surfaces  106 C 1 - 106 C 4  are offset from each other in the direction along rotational axis A. As a result, the different reflection sectors  104 C 1 - 104 C 4  generate a successive array of offset output beams  112  that are translationally (and/or angularly) offset from each other, as explained below in greater detail. 
     In some embodiments, reflection surfaces  106 C 1 - 106 C 4  are planar surfaces that are parallel to each other, such that the array of reflected output beams  112  produced by the input radiation beam successively reflecting off the reflection surfaces  106 C 1 - 106 C 4  as element  100 C rotates are translationally offset and parallel to each other, e.g., as discussed with reference to the array of output beams  112 A- 112 D shown in  FIG. 13 . In some embodiments, the plane of each respective reflection surface  106 C 1 - 106 C 4  is perpendicular to rotational axis A. In other embodiments, the planes of reflection surfaces  106 C 1 - 106 C 4  may be parallel to each other, but arranged at any non-perpendicular angle relative to rotational axis A. 
     In other embodiments, reflection surfaces  106 C 1 - 106 C 4  are planar surfaces arranged at angles relative to each other such that the array of reflected radiation beams are both translationally offset and angularly offset (i.e., not parallel) from each other; for example, the reflected array of beams (as opposed to the individual reflected beams) may diverge or converge, or form multiple rows of treatment spots, as opposed to a single linear row. 
     Forming reflection surfaces  106 C 1 - 106 C 4  as planar surfaces perpendicular to the rotational axis provides the effect that for the duration of time that the radiation beam is reflected off each reflection surface  106 C, the angular direction of the resulting output beam  112  (relative to the device structure or housing  24 ) remains constant over the duration of time, which may be referred to as “constant angular deflection” output beams  112 . “Constant angular deflection” is discussed in greater detail below with reference to  FIGS. 26A-26B . Thus, in such embodiments, reflection sectors  104 C 1 - 104 C 4  may be referred to as constant angular deflection reflection sectors  104 C, similar to the constant angular deflection lenslets  104 A and  104 B discussed above with respect to certain embodiments of the disc-shaped and cup-shaped scanning elements  100 A and  100 B. 
     In some embodiments, some or all reflection surfaces  106 C 1 - 106 C 4  may be non-planar, e.g., concave or convex along one or more axes. In such embodiments, each output beam  112  may either (a) move relative to the device structure or housing  24  during the time that the input beam  110  is incident upon the respective non-planar reflection surface  106 C, or (b) remain substantially stationary relative to the device structure or housing  24  during the time that the input beam  110  is incident upon the respective non-planar reflection surface  106 C, depending on the specific non-planar shape of reflection surfaces  106 C 1 - 106 C 4  and/or other aspects of the configuration of optics  16 , for example. 
     For example, reflection surfaces  106 C 1 - 106 C 4  may be shaped or configured as “shifting deflection” surfaces that provide shifting deflection output beam  112 , similar to the shifting deflection lenslets  104 A and  104 B discussed above with respect to certain embodiments of the disc-shaped and cup-shaped scanning elements  100 A and  100 B. “Shifting deflection” is discussed in greater detail below with reference to  FIGS. 27A-27B . 
     As discussed above, reflection surfaces  106 C 1 - 106 C 4  may be offset from each other in the direction of the axis A. Reflection surfaces  106 C 1 - 106 C 4  may be offset from each other along the axis A by the same distance between each surface, or alternatively, by different distances. The offset distance between different reflection surfaces  106 C 1 - 106 C 4  may be selected to provide the desired spacing between the respective output beams  112  reflected off reflection surfaces  106 C 1 - 106 C 4 . 
       FIG. 13  illustrates a representational side view of rotating element  100 C, with each reflection surface  106 C 1 - 106 C 4  represented by a line extending across the diameter of body  102 C, for illustration purposes. An input beam  110  reflects off each reflection surface  106 C 1 - 106 C 4  in succession, one at a time, as rotating element  100 C rotates about axis A, to produce a successive array of output beams  112 A- 112 D. In this example, reflection surfaces  106 C 1 - 106 C 4  are planar surfaces and parallel to each other, such that reflected output beams  112 A- 112 D are translationally offset and parallel to each other, and stationary with respect to the device structure or housing  24  (i.e., constant angular deflection output beams). 
       FIG. 14  illustrates a side view of another rotating element  100 C, wherein the element body  102 C has a tapered shape, according to certain embodiments. As with  FIG. 13 , each reflection surface  106 C 1 - 106 C 4  is represented by a line extending across the diameter of body  102 C, for illustration purposes. The tapered shape of body  102 C may reduce the mass of body  102 C and/or may prevent unwanted deflection or blocking of the input beam  110  and/or output beams  112 A- 112 D by the structure of body  102 C. 
     Downstream Optics for Stair-Stepped Scanning System 
     As mentioned above, the successive array of output beams  112  may be delivered directly to the skin  40  as delivered beams  114 , or may be influenced by one or more downstream optics  60 B (with reference to  FIG. 3A ) before being delivered to the skin  40  as delivered beams  114 . In some embodiments, one or more downstream optics  60 B may be configured to redirect and/or otherwise influence the array of output beams  112 . Such downstream optics  60 B may include any one or more mirrors or other reflective surfaces, lenses or other optical elements configured to deflect, focus, defocus, or otherwise affect the direction, convergence/divergence, focal point, beam intensity profile, and/or other property of output beams  112 . 
     In some embodiments, downstream optics  60 B may be configured to influence the intensity profile of individual output beams  112  along one axis or multiple axes, e.g., by influencing the shape of the intensity profile along one or more axis, changing whether the beam is converging, diverging, or collimated along one or more axis, changing the degree of convergence or divergence along one or more axis, etc., For example, downstream optics  60 B may be configured to define a focal point or focal plane for each output beam  112  at or slightly above the surface of the skin (i.e., outside the skin). Downstream optics  60 B may influence the intensity profile of each individual output beams  112  equally or differently. For example, in some embodiments, such downstream optics may include an array of lens or mirror elements, each corresponding to an individual output beam  112  and thus operable to influence individual output beams  112  as desired, including influencing individual output beams  112  differently if desired. 
     In addition or alternatively, downstream optics  60 B may be configured to deflect output beams  112 . Downstream optics  60 B may deflect output beams  112  in a manner that does not influence the propagation of output beams  112  relative to each other. For example, in the example shown in  FIG. 15A , downstream optics  60 B include a planar mirror  150 A that reflects an array of output beams  112 A- 112 D from rotating element  100 C towards the skin  40 , without influencing the propagation of output beams  112  relative to each other. In some embodiments, downstream optics  60 B may be configured to deflect at least some of the output beams  112  to increase the normality (i.e., perpendicularity) of such beams  112  relative to the target surface. In other embodiments, downstream optics may be configured to deflect at least some of the output beams  112  to deliver the beams  112  at one or more predetermined normal or non-normal (i.e., non-perpendicular) angle relative to the target surface. 
     Alternatively, downstream optics  60 B may deflect output beams  112  in a manner that influences the propagation of output beams  112  in one or more axes relative to each other, such as (a) influencing whether the array of output beams  112  (as opposed to individual output beams  112 ) converge, diverge, or propagate parallel to each other, and/or (b) influencing the degree with which the array of output beams  112  (as opposed to individual output beams  112 ) converge or diverge from each other. For example, such downstream optics  60 B may include one or more lenses or mirror elements that are concave, convex, or otherwise non-planar in one or more directions. 
       FIGS. 15B and 15C  illustrate examples of such downstream optics. In the example embodiment of  FIG. 15B , downstream optics include a convex mirror  150 B that increases the divergence/decreases the convergence of an array of output beams  112 A- 112 D, thus either (a) converting a parallel array to a diverging array, (b) increasing the degree of divergence of a diverging array, (c) decreasing the degree of convergence of a converging array, or (d) converting a converging array to a parallel or diverging array. In contrast, in the example embodiment of  FIG. 15C , downstream optics include a concave mirror  150 C that increases the convergence or decreases the divergence of an array of output beams  112 A- 112 D, thus either (a) converting a parallel array to a converging array, (b) increasing the degree of convergence of a converging array, (c) decreasing the degree of divergence of a diverging array, or (d) converting a diverging array to a parallel or converging array. 
     In some embodiments, downstream optics  60 B may both (a) influence the intensity profile of individual output beams  112  along one or more axis, and (b) influence the propagation of output beams  112  relative to each other along one or more axis. 
     Path Length Compensation 
     In certain applications, it may be desirable that each beam delivered to the skin  40  has an equal total path length, the total path length being defined as the total travel distance of the beam from the radiation source  14  to the skin  40 . For example, in embodiments in which individual beams delivered to the skin  40  are converging, diverging, or otherwise experiencing a change in intensity profile (in one or more axis) while propagating toward the skin  40 , it may be desired that each beam have an equal path length from the radiation source  14  to the skin  40  to provide a uniform size, shape, and/or intensity of treatment spots on the skin  40  created by the different individual beams. 
     However, as shown in the example embodiments of  FIGS. 13 and 14 , the input beam  110  travels different distances before reflecting off the respective reflection surface  106 C 1 - 106 C 4 . Thus, in some embodiments, downstream optics may include path length compensation optics  152 . Path length compensation optics  152  may include any suitable one or more optical elements to reflect, deflect, or otherwise influence the output beams  112 A- 112 D in order to provide equal total path lengths (e.g., from the radiation source  14  to the skin  40 ). 
       FIG. 16  illustrates an example of path length compensation optics  152 , according to certain embodiments. In this example, path length compensation optics  152  includes a single deflecting element (e.g., mirror or lens) arranged to deflect output beams  112 A- 112 D such that the path length of each beam from the radiation source  14  to optics  152  is equal. Thus, in this example, path length OAE=path length OBF=path length OCG=path length ODH. Optics  152  may be arranged parallel to the skin  40  such that the total path length of each beam is equal. For example, optics  152  may deflect each output beam  112 A- 112 D perpendicular to the page and toward the plane of the skin  40  arranged generally parallel to the page. 
     In other embodiments, path length compensation optics  152  may be arranged non-parallel to the skin  40 , but still provide that the total path length of each beam is equal. For example, optics  152  may be arranged such that a portion of the path length differences from point O to points A-D on the different reflection surfaces  106 C 1 - 106 C 4  is compensated for by the different respective distances between points A-D on rotating element  30  and points E-H on optics  152 , while the remainder of the path length differences is compensated for by the different respective distances between points E-H on optics  152  and the skin  40 . 
     In other embodiments, e.g., as shown in  FIG. 18B  discussed below, path length compensation optics  152  may include multiple optical elements, each corresponding to an individual output beam  112 . 
     As with other downstream optics discussed above, path length compensation optics  152  (a) may or may not influence the intensity profile of individual output beams  112  along one or more axis, and (b) may or may not influence the propagation of output beams  112  relative to each other along one or more axis. 
     Example Stair-Stepped Beam Scanning Element 
       FIGS. 17 and 18  illustrate example embodiments of a rotating stair-stepped beam scanning element  100 C. In particular,  FIG. 17A  illustrates an example three-dimensional view,  FIG. 17B  illustrates an example end view of element  100 C viewed along the axis of rotation A,  FIG. 18A  illustrates an example side view of stair-stepped scanning element  100 C, and including a first example path length compensation optics  152  (single element), and  FIG. 18B  illustrates another example side view of stair-stepped scanning element  100 C, and including a second example path length compensation optics  152  (multiple elements). 
     As shown in  FIGS. 17A and 17B , the illustrated example includes 12 reflection sectors  104 C, each defining a planar reflection surface  106 C that is perpendicular to the axis of rotation A of rotating element  100 C, the planar reflection surfaces  106 C being parallel to each other and offset from each other in the direction of the axis of rotation A. Further, each reflection sector  104 C also defines a tapered side surface  108 C such that the reflection sector  104 C together define a generally conical stepped shape. 
     As shown in  FIG. 18A , the 12 planar reflection surfaces  106 C of rotating element  100 C may reflect a stationary input beam  110  to generate a time-sequential array of 12 output beams  112  that are translationally offset from (and parallel to) each other). As discussed above, path length compensation optics  152  may be provided to compensate for the different path lengths of the input beam  110  incident on the different reflection surfaces  106 C of rotating element  100 C, in order to provide a uniform total path length (e.g., from radiation source  14  to the skin  40 ) for each output beam  112 . In this embodiment, path length compensation optics  152  comprises a single optical element configured to deflect the time-sequential array of output beams  112  toward the skin  40  (or toward further downstream optics before delivery to the skin  40 ). 
       FIG. 18B  illustrates an alternative embodiment of  FIG. 18A , wherein path length compensation optics  152  comprises an array of optical elements  158 , each arranged for deflecting one of the output beams  112  toward the skin  40  (or toward further downstream optics before delivery to the skin  40 ). 
     Reflection Sector Configuration 
     Returning to  FIGS. 17A and 17B , the illustrated embodiment includes 12 reflection sectors  104 C 1 - 104 C 12  arranged around the circumference in the order  104 C 1 ,  104 C 2 ,  104 C 3 , . . .  104 C 12 . The 12 reflection sectors define two sets, reflection sectors  104 C 1 - 104 C 6  and reflection sectors  104 C 7 - 104 C 12 , each set defining a group of six consecutive ascending steps, and each set extending 180 degrees around body  102 C. 
     In other embodiments, reflection sectors  104 C may define one set of consecutively adjacent ascending steps around the circumference, or any multiple number of sets of consecutively adjacent ascending steps around the circumference. 
     Alternatively, reflection sectors  104 C may be arranged in sets that are not consecutively adjacent. For example, two sets of reflection sectors  104 C 1 - 104 C 6  and  104 C 7 - 104 C 12 , each forming a series of (consecutive or non-consecutive) ascending steps, may be arranged in a partial or fully alternating manner around the circumference (e.g., [ 104 C 1 ,  104 C 7 ,  104 C 2 ,  104 C 8 , . . .  104 C 6 ,  104 C 12 ], or [ 104 C 1 ,  104 C 2 ,  104 C 3 ,  104 C 7 ,  104 C 7 ,  104 C 9 ,  104 C 4 ,  104 C 5 ,  104 C 6 ,  104 C 10 ,  104 C 11 ,  104 C 12 ]). 
     As another example, three sets of reflection sectors  104 C 1 - 104 C 4 ,  104 C 5 - 104 C 8 , and  104 C 9 - 104 C 12 , each forming a series of (consecutive or non-consecutive) ascending steps, may be arranged in a partial or fully alternating manner around the circumference (e.g., [ 104 C 1 ,  104 C 5 ,  104 C 9 ,  104 C 2 ,  104 C 6 ,  104 C 10 ,  104 C 3 ,  104 C 7 ,  104 C 11 ,  104 C 4 ,  104 C 8 ,  104 C 12 ], or [ 104 C 1 ,  104 C 2 ,  104 C 5 ,  104 C 6 ,  104 C 9 ,  104 C 10 ,  104 C 3 ,  104 C 4 ,  104 C 7 ,  104 C 8 ,  104 C 11 ,  104 C 12 ]). 
     Alternatively, reflection sectors  104 C may define sets that are not arranged in a consecutively adjacent or alternating order. For example, sets of reflection sectors  104 C may be arranged randomly around the circumference of body  102 C. For example, three sets of reflection sectors  104 C 1 - 104 C 4 ,  104 C 5 - 104 C 8 , and  104 C 9 - 104 C 12 , each forming a series of consecutive ascending steps 1-4, may be arranged in an alternating random manner around the circumference (e.g., [ 104 C 1 ,  104 C 5 ,  104 C 10 ,  104 C 4 ,  104 C 8 ,  104 C 12 ,  104 C 3 ,  104 C 6 ,  104 C 11 ,  104 C 2 ,  104 C 7 ,  104 C 9  (alternating between the three sets)]), or a fully random manner (e.g., [ 104 C 7 ,  104 C 2 ,  104 C 8 ,  104 C 5 ,  104 C 12 ,  104 C 10 ,  104 C 3 ,  104 C 6 ,  104 C 1 ,  104 C 11 ,  104 C 4 ,  104 C 9 ]). 
     As discussed above, reflection surfaces  106 C may be arranged parallel to each other, or non-parallel to each other. In the example embodiment shown in  FIGS. 17A-17B , planar reflection surfaces  106 C are all parallel to each other. Embodiments in which planar reflection surfaces  106 C are all parallel to each other may be configured for either single-scan-direction, single-row scanning or single-scan-direction, multi-row scanning, which terms are defined below with reference to  FIGS. 23A-24B . Embodiments in which at least some planar reflection surfaces  106 C are not parallel to each other may be configured for multi-scan-direction scanning, which is defined below with reference to  FIGS. 25A-25B . 
       FIGS. 19 and 20  illustrate example optical systems  15  that include a stair-stepped rotating scanning element  100 C, according to certain embodiments. As shown, each of the example optical systems  15  of  FIGS. 19 and 20  includes (a) fast axis optics  64 , (b) slow axis optics  66 , (c) stair-stepped scanning element  100 C, and (d) downstream optics  60 B, specifically a mirror  150 . Each optical system  15  receives a beam  108  generated by a radiation source  14 , treats the generated beam  108  to provide an input beam  110  to stair-stepped scanning element  100 C, which converts the input beam  110  into a time-sequential series of output beams  112 , and further treats the output beams  112  to provide delivered beams  114  to the skin  40  to generate a pattern of treatment spots  70 . The beam extending from radiation source  14  to the skin  40  during any particular treatment spot formation, which includes generated beam  108 , input beam  110 , an output beam  112 , and the corresponding delivered beam  114 , is referred to herein as beam  80 . 
     As discussed above, fast axis optics  64  include one or more optical elements configured to primarily affect the fast axis profile of the beam, while slow axis optics  66  include one or more optical elements configured to primarily affect the slow axis profile of the beam. 
     In certain embodiments, radiation source  14  may generate an axially-asymmetric beam  108  having different beam profiles in the fast axis and slow axis. For example, radiation source  14  may comprise a laser diode. In other embodiments, radiation source  14  may generate axially-symmetric beam, e.g., a fiber laser or other axially-symmetric radiation source. 
     Each of the example embodiments shown in  FIGS. 19 and 20  includes a single fast axis optical element  64 , and a single slow axis optical element  66  distinct from the fast axis optical element  64 . In other embodiments, device  10  includes multiple fast axis optical elements  64  and a single slow axis optical element  66  distinct from the fast axis optical elements  64 . In other embodiments, device  10  includes a single fast axis optical element  64  and multiple slow axis optical elements  28  distinct from the fast axis optical element  64 . 
     In still other embodiments, one or more fast axis optical element  64  and slow axis optical element  66  may be integrated, i.e., a single optical element (or multiple optical elements) may substantially act on both the fast axis and slow axis intensity profiles. Such elements may be referred to as multi-axis optical elements. Such embodiments may include one or more multi-axis optical elements in combination with zero, one, or more fast axis optical elements  64 , and zero, one, or more slow axis optical elements  28 . Thus, as an example only, device  10  may include a single fast axis optical elements  64 , a single slow axis optical elements  28 , and a single multi-axis optical element. 
     In some embodiments, fast axis optics  64  (either a single element or multiple elements, depending on the embodiment) may be configured to affect the fast axis intensity profile of beam  80  (i.e., input beam  110  and/or output beam  112 ) without substantially affecting the slow axis intensity profile, and slow axis optics  66  (either a single element or multiple elements, depending on the embodiment) may be configured to affect the slow axis intensity profile of the beam  80  without substantially affecting the fast axis intensity profile. Or, fast axis optics  64  (either a single element or multiple elements, depending on the embodiment) may be configured to affect the fast axis intensity profile of the beam  80  to a significantly greater extent or degree than the slow axis intensity profile, and slow axis optics  66  (either a single element or multiple elements, depending on the embodiment) may be configured to affect the slow axis intensity profile of the beam  80  to a significantly greater extent or degree than the fast axis intensity profile. 
     In other embodiments, one of fast axis optics  64  (either a single element or multiple elements, depending on the embodiment) or slow axis optics  66  (either a single element or multiple elements, depending on the embodiment) substantially affects only the fast axis intensity profile or the slow axis intensity profile, while the other of fast axis optics  64  and slow axis optics  66  substantially affects both the fast axis intensity profile and the slow axis intensity profile. Or, one of fast axis optics  64  (either a single element or multiple elements, depending on the embodiment) or slow axis optics  66  (either a single element or multiple elements, depending on the embodiment) affects one of the fast and slow axis intensity profiles of beam  80  to a significantly greater extent or degree than the other of the fast and slow axis intensity profiles, while the other of fast axis optics  64  and slow axis optics  66  affects both the fast axis intensity profile and the slow axis intensity profile to a substantially similar extent or degree. 
     In other embodiments, each of the fast axis optics  64  (either a single element or multiple elements, depending on the embodiment) or slow axis optics  66  (either a single element or multiple elements, depending on the embodiment) are configured to significantly affect both the fast axis intensity profile and the slow axis intensity profile of the beam  80 . 
     Returning to  FIGS. 19 and 20 , each of these example embodiments includes (a) a scanning system  48  including a stair-stepped rotating scanning element  100 C, and (b) downstream optics  60 B, specifically a mirror  150 , which are both distinct from both the fast axis optical element  64  and slow axis optical element  66 . In this embodiment, rotating scanning element  100 C utilizes planar reflection surfaces  106 C such that rotating scanning element  100 C does not significantly affect the intensity profile of the beam  80  in any axis. In other embodiments, reflection surfaces  106 C of rotating scanning element  100 C may be configured to significantly affect the intensity profile in one or more axis (e.g., the fast axis intensity profile and/or the slow axis intensity profile). 
     In other embodiments, stair-stepped rotating scanning element  100 C may be integrated with fast axis optics  64  and/or slow axis optics  66 . For example, stair-stepped rotating scanning element  100 C may act as a fast axis optical element  64  (as the only fast axis optical element, or in combination with one or more other fast axis optical elements  64 ), with slow axis optics  66  being provided separately. Alternatively, stair-stepped rotating scanning element  100 C may act as a slow axis optical element  66  (as the only slow axis optical element, or in combination with one or more other slow axis optical elements  66 ), with fast axis optics  64  being provided separately. Alternatively, stair-stepped rotating scanning element  100 C may act as both a fast axis optical element  64  and a slow axis optical element  66  (as a single, combined scanning element/fast axis optical element/slow axis optical element; or in combination with one or more other fast axis optical elements  64  and/or one or more other slow axis optical elements  66 ). 
     Fast axis optical element  64 , slow axis optical element  66 , and stair-stepped rotating scanning element  100 C may be arranged in any order along the path of the beam  80 . For example, fast axis optical element  64  and slow axis optical element  66  may be arranged upstream of stair-stepped rotating scanning element  100 C (as shown in  FIGS. 19 and 20 ), or downstream of stair-stepped rotating scanning element  100 C, or stair-stepped rotating scanning element  100 C may be arranged between optical elements  64  and  66 . Further, optical elements  64  and  66  may be arranged in any order with respect to each other. 
     In addition to deflecting an input beam  110  to generate an array of offset output beams  112  (e.g., offset along a scan direction), each sector  104  may further influence the input beam  110  in one or more axis. For example, each sector  104  may further influence the input beam  110  by having curvature in its reflection surface that provides optical power, similar to the examples provided above for the transmissive disk or cup shaped scanning elements. For example, in addition to the deflection, each sector  104  may further act as a slow axis optic and/or a fast axis optic. In some embodiments, each sector  104  may deflect the input beam  110  in the slow axis direction, and also influence the convergence/divergence of the input beam  110 . For example, element  100  may receive an input beam  110  that is diverging in the slow axis direction, and each sector  104  may both (a) deflect the input beam  110  by a particular degree, and (b) convert the diverging beam into a collimated or converging beam, e.g., such that individual collimated, focused, or pseudo-focused output beams  112  can be delivered to the target area, for generating treatment spots. 
     Example Configurations of Rotating Element  100  and Corresponding Treatment Spot Arrays 
     As discussed above with respect to  FIGS. 6A-6C , beam scanning element  100  may be configured to provide a wide variety of treatment spot patterns on the skin  40 , and treatment spots may be delivered in any desired sequential order, based on the particular configuration and arrangement of sectors  104   1  to  104   n . 
       FIG. 21A  illustrates an example beam scanning element  100 , which may be configured as a disc-shaped scanning element (e.g., disc-shaped transmissive element  100 A), a cup-shaped scanning element (e.g., cup-shaped transmissive element  100 B), a stair-stepped scanning element (e.g., stair-stepped reflective element  100 C), or any other type of rotating scanning element. Element  100  has a body  102  configured to rotate about an axis A. Body  102  includes a plurality of sectors  104  generally arranged around the circumference or periphery of the body  12  and configured to deflect an input beam  110  into an array of output beams  112  offset from each other. Depending on the particular embodiment, each sector  104  may transmit but deflect the input beam  110 , as indicated by example arrow  112 A (e.g., disc-shaped transmissive element  100 A or cup-shaped transmissive element  100 B discussed below) or reflect the input beam, as indicated by example arrow  112 B (e.g., stair-stepped reflective element  100 C discussed below). 
     Sectors  104   1  to  104   n  may be configured such that the array of treatment spots may be delivered in any desired sequential order (e.g., in terms of the amount of deflection in a particular direction) and/or to produce one, two, or more rows during each scan of element  100 , as discussed below. 
     Sequential Order of Treatment Spots 
     Sectors  104   1  to  104   n  may be configured such that the array of treatment spots  70  may be delivered in any desired sequential order, e.g., with respect to one or more particular directions. For example, in the example shown in  FIG. 21A , sectors  104   1  to  104   n  are labeled A through L, with sector A (sector  104   1 ) producing the greatest offset (in one or more directions), sector B (sector  104   2 ) producing the next greatest offset, sector C (sector  104   3 ) producing the next greatest offset, and so on. As shown, sectors A-L are arranged in sequential order around the perimeter of element  100 . 
     Thus,  FIG. 21B  illustrates the sequential order of treatment spots delivered by one full rotation of element  100  (i.e., one scan of input beam  110 ), assuming device  10  is held stationary with respect to the target area (e.g., device  10  operating in a stamping mode, as discussed above). As shown, the treatment spots are labeled 1 through 12, indicating the sequential order in which each treatment spot is produced, beginning with treatment spot  1  produced by sector A (sector  1040 , followed by treatment spot  2  produced by sector B (sector  104   2 ), and so on. 
     Further,  FIG. 21C  illustrates the sequential order of treatment spots delivered by one full rotation of element  100  (i.e., one scan of input beam  110 ), assuming device  10  is manually glided over the target area in a direction substantially perpendicular to the scan direction (e.g., device  10  operating in a gliding mode, as discussed above). As shown, the treatment spots are again labeled 1 through 12, indicating the sequential order in which each treatment spot is produced, beginning with treatment spot  1  produced by sector A (sector  104   1 ), followed by treatment spot  2  produced by sector B (sector  104   2 ), and so on. This configuration of element  100  produces a generally linear row of treatment spots aligned diagonally with respect to the scan direction due to the movement of the device in the glide direction. 
     Element  100  may be configured to generate treatment spots in any other desired sequential order. For example,  FIG. 22A  illustrates an example element  100 ′ that, like example element  100  discussed above, includes sectors  104   1  to  104   n  numbered A through K, with sector A (sector  104   1 ) producing the greatest offset (in one or more directions), sector B (sector  104   2 ) producing the next greatest offset, sector C (sector  104   3 ) producing the next greatest offset, and so on. However, unlike element  100  discussed above, sectors A-L of element  100 ′ are not arranged sequentially around the perimeter of element  100 . Rather, sectors A-L are arranged in a specific pseudo-random order around the perimeter of element  100 : A, C, E, I, G, B, D, F, K, J, H, L. 
       FIG. 22B  illustrates the sequential order of treatment spots delivered by one full rotation of element  100 ′ (i.e., one scan of input beam  110 ), assuming device  10  is held stationary with respect to the target area (e.g., device  10  operating in a stamping mode). As shown, the treatment spots are labeled 1 through 12, indicating the sequential order in which each treatment spot is produced, beginning with treatment spot  1  produced by sector A (sector  1040 , followed by treatment spot  2  produced by sector C (sector  104   2 ), followed by treatment spot  3  produced by sector E (sector  104   3 ), and so on. 
     Further,  FIG. 22C  illustrates the sequential order of treatment spots delivered by one full rotation of element  100 ′ (i.e., one scan of input beam  110 ), assuming device  10  is glided over the target area in a direction substantially perpendicular to the scan direction (e.g., device  10  operating in a gliding mode). As shown, the treatment spots are again labeled 1 through 15, indicating the sequential order in which each treatment spot is produced, beginning with treatment spot  1  produced by sector A (sector  104   1 ), followed by treatment spot  2  produced by sector C (sector  104   2 ), followed by treatment spot  3  produced by sector E (sector  104   3 ), and so on. Thus, each scan of element  100 ′ produces a non-linear, pseudo-random pattern of treatment spots. In some embodiments or applications, repeating a non-linear scan pattern (e.g., the pattern shown in  FIG. 22C ) in a gliding mode of device  10  may provide a more uniform or otherwise preferred array (e.g., generates less pain or less thermal interaction between the micro-thermal zones (MTZs) underlying the treatment spots than that produced by a linear scan pattern (e.g., the pattern shown in  FIG. 21C ). In other embodiments or applications, repeating a linear scan pattern in a gliding mode may provide a more uniform or otherwise preferred array of treatment spots than that produced by a non-linear scan pattern. 
     It should be understood that the configurations and resulting treatment spot patterns shown in  FIGS. 21 and 26  are examples only, and that beam scanning element  100  may be configured to generate treatment spots in any other desired sequential order. Further, element  100  may have any other number (more or less than 12) of sectors for generating any other number (more or less than 12) of treatment spots per rotation of element  100 . Further, element  100  may be produced in any suitable manner. For example, element  100  may be formed as a single, integral element. As another example, the individual sectors  104  may be formed separately and then secured to each other to form element  100 . As a further example, it can be understood by one of ordinary skill in the filed that element  100  may be produced by many well-known fabrication methods including injection molding, grinding, machining, electroforming, and further including with or without secondary processes such as polishing, platings, or coatings. 
     Other Example Treatment Spot Patterns Generated by Element  100   
     In addition to the sequential order of treatment spot generated by beam scanning element  100 , the number of rows of treatment spots  70  generated by each rotation of element  100  (i.e., each scan of input beam  110 ) may vary based on the configuration of element  100 . For example, element  100  may be configured to provide “single-scan-direction, single-row scanning,” “single-scan-direction, multi-row scanning,” or “multi-scan-direction, multi-row scanning,” as discussed below. 
     1. Single-Scan-Direction, Single-Row Scanning 
       FIGS. 23A-23B  illustrate example radiation patterns generated by a single-scan-direction, single-row scanning element  100  that includes 12 sectors  104   1 - 104   12  arranged in the order  104   1 ,  104   2 ,  104   3  . . .  104   12 . The sectors  104   1 - 104   12  are configured such that the treatment spots are generated in a single row, in order along the direction of row (i.e., each new treatment spot being adjacent to the previous treatment spot). For stair-stepped scanning element  100 C, single-scan-direction, single-row scanning can be provided where the reflective sectors  104 C are arranged as a single series of consecutive ascending steps around the perimeter of element  100 C. 
       FIG. 23A  illustrates the treatment spot pattern formed on the skin  40  during one full rotation of element  100  (i.e., one scan of input beam  110 ) if the device  10  is held stationary relative to the skin  40 , as well as indicating the sequential order of the generated treatment spots ( 1 - 12 ) and the sector  104   1 - 104   12  that produced each treatment spot.  FIG. 23B  illustrates the treatment spot pattern formed on the skin  40  if the device  10  is moved at a relatively constant speed across the skin  40  during the scanning and radiation delivery process in a glide direction generally perpendicular to the scan direction.  FIG. 23B  shows a first scan, indicated as “Scan  1 ”, created by one rotation of element  100 , and the first four spots of a second scan, indicated as “Scan  2 ,” as well as indicating the sequential order of the generated treatment spots ( 1 - 16 ) and the sector  104   1 - 104   12  that produced each treatment spot. 
     As shown, a full scan (i.e., a full rotation of element  100 ) generates one row of treatment spots. Thus, such patterns are referred to herein as “single-scan-direction, single-row scanning patterns.” A two-dimensional array of treatment spots can be produced in the skin  40  by repeating (continuously or non-continuously) the single-scan-direction, single-row scanning pattern while device  10  is physically moved across the skin  40 . 
     2. Single-Scan-Direction, Multi-Row Scanning 
       FIGS. 24A-24B  illustrate example radiation patterns generated by a single-scan-direction, multi-row scanning element  100  that includes 12 sectors  104   1 - 104   12  arranged in the order  104   1 ,  104   2 ,  104   3  . . .  104   12 . The sectors  104   1 - 104   12  are configured such that the treatment spots are generated in a single row, but out of order along the direction of the row.  FIG. 24A  illustrates the treatment spot pattern formed on the skin  40  during one rotation of element  100  if the device  10  is held stationary relative to the skin  40 , as well as the sequential order of the generated treatment spots ( 1 - 12 ) and the sector  104   1 - 104   12  that produced each treatment spot. 
       FIG. 24B  illustrates the treatment spot pattern formed on the skin  40  if the device  10  is moved at a relatively constant speed across the skin  40  during the scanning and radiation delivery process in a glide direction generally perpendicular to the scan direction. As shown, a full scan (i.e., a full rotation of element  100 ) essentially generates two rows of treatment spots, one corresponding to sectors  104   1 - 104   6  and one corresponding to sectors  104   7 - 104   12 . 
     Thus,  FIG. 24B  shows a first scan, indicated as “Scan  1 ”, created by one rotation of element  100 , and the first three spots of a second scan, indicated as “Scan  2 ,” as well as indicating the sequential order of the generated treatment spots ( 1 - 15 ) and the sector  104   1 - 104   12  that produced each treatment spot. The first scan includes a first row created by sequentially scanning sectors  104   1 - 104   6 , followed by a second row created by sequentially scanning sectors  104   7 - 104   12 . In this manner, a multi-row scanning pattern can be created using a single-scan-direction scanner (e.g., a single-scan-direction scanning element  100 ). Such patterns are referred to herein as “single-scan-direction, multi-row scanning patterns.” 
     Single-scan-direction, multi-row scanning patterns have any other number of rows (i.e., more than two) can be similarly created. For example, an element  100  may include 12 sectors  104   1 - 104   12  configured such that sectors  104   1 - 104   4  generate a first row, sectors  104   5 - 104   8  generate a second row, and sectors  104   9 - 104   12  generate a third row. Thus, the sectors may be arranged around element  100  in the order:  104   1 ,  104   5 ,  104   9 ,  104   2 ,  104   6 ,  104   10 ,  104   3 ,  104   7 ,  104   11 ,  104   4 ,  104   8 ,  104   12 . 
     Further, a larger two-dimensional array of treatment spots can be produced in the skin  40  by repeating (continuously or non-continuously) such single-scan-direction, multi-row scanning patterns while device  10  is physically moved across the skin  40 . 
     For stair-stepped scanning element  100 C, single-scan-direction, multi-row scanning can be provided by arranging the reflective sectors  104 C in multiple groups of consecutively ascending steps around the perimeter of element  100 C, with each group of consecutively ascending steps generating a row of treatment spots during a gliding operation. For example, to produce the example pattern shown in  FIG. 24B  a stair-stepped scanning element  100 C having 12 reflection sectors arranged in order  104   1 - 104   12  around the perimeter of element  100 C may consist of two groups of consecutively ascending steps: sectors  104   1 - 104   6  define a first set of ascending steps (which generate the first row of spots), and sectors  104   7 - 104   12  define a second set of ascending steps (which generate the second row of spots). The embodiment of stair-stepped scanning element  100 C shown in  FIGS. 17A-17B  illustrates an example of such a configuration. 
     In other embodiments, the single-scan-direction rotating element may be otherwise configured to deliver beams in any other sequential order along the scan direction, e.g., based on the number and arrangement of sets of sectors  104 . Further, any of such single-scan-direction radiation patterns may be repeated (continuously or non-continuously) while device  10  is moved across the skin  40  in order to form a larger two-dimensional array of treatment spots. 
     3. Multi-Scan-Direction Scanning 
     In other embodiments, a multi-scan-direction rotating element  100  is used. A multi-scan-direction rotating element  100  scans an input beam  110  in multiple directions, such that treatment spots generated by a single scan (i.e., a single rotation of the rotating element  100 ) are not aligned in a single linear row, even when the device  10  is held stationary during the scan. For example, a multi-scan-direction rotating element  100  may be configured to produce multiple offset rows of treatment spots in a single rotation of the scanning element. Such resulting patterns are referred to herein as “multi-scan-direction, multi-row scanning patterns.” As opposed to a single-scan-direction element  100  configured to form multiple rows in a single scan by moving the device  10  across the skin  40  during the scan, a multi-scan-direction rotating element  100  can form multiple rows in a single scan as a result of the beam scanning itself, regardless of whether the device  10  is moved across the skin  40  during the scan. For example, a single scan of multi-scan-direction rotating element  100  may form multiple rows of treatment spots, in which each row is scanned in a primary scan direction, and the rows are offset from each other in a secondary scan direction, which may be orthogonal to the primary scan direction (e.g., as shown in  FIGS. 29A and 29B  discussed below). 
     In some embodiments, multi-scan-direction rotating elements  100  include multiple subsets of sectors  104 , each configured to produce a different row of treatment spots, regardless of whether the device  10  is moved across the skin  40  during the scan. For example, element  100  for generating three rows of treatment spots (while device  10  remains stationary) may include a first set of sectors  104   1 - 104   n  configured to generate a first row of treatment spots, a second set of sectors  104   n+1 - 104   2n  configured to generate a second row of treatment spots, and a third set of sectors  104   2n+1 - 104   3n  configured to generate a third row of treatment spots. 
     In embodiments in which sectors  104  are lenslets (e.g., element  100 A or  100 B), the lenslets may be shaped or aligned to deflect input beam  110  to form rows of output beams  112  offset from each other in a secondary scan direction. Embodiments of stair-stepped element  100 C may include multiple sets of reflection sectors  104 , each set having reflection surfaces  106  parallel with each other but angularly offset from the reflection surfaces  106  of the other set(s) of reflection sectors  104 . Thus, each set of sectors  104  may generate a separate row of treatment spots offset from each other. An example is discussed below with respect to  FIGS. 29A-29B . Sectors  104  of such a multi-scan-direction rotating element  100  may be configured in any suitable number of sets to produce any suitable number of rows of treatment spots during a single scan. 
       FIGS. 25A-25B  illustrate example multi-scan-direction, multi-row scanning patterns generated using a multi-scan-direction scanning element  100 .  FIG. 25A  illustrates the treatment spot pattern formed on the skin  40  during one rotation of the example multi-scan-direction scanning element  100  discussed above, where the device  10  is held stationary relative to the skin  40 , as well as indicating the sequential order of the generated treatment spots ( 1 - 12 ) and the sector  104  ( 104   1 - 104   12 ) that produced each treatment spot. 
       FIG. 25B  illustrates the treatment spot pattern formed by the example multi-scan-direction scanning element  100  if the device  10  is moved at a constant speed across the skin  40  during the scanning and radiation delivery process in a glide direction generally perpendicular to the scan direction. As shown, each full scan (i.e., a full rotation of element  100 ) essentially generates two rows of treatment spots, one corresponding to each of the two sets of sectors  104   1 - 104   6  and  104   7 - 104   12 . Thus,  FIG. 25B  shows a full first scan, indicated as “Scan  1 ”, created by one rotation of element  100 , and a full second scan, indicated as “Scan  2 ,” as well as indicating the sequential order of the generated treatment spots ( 1 - 24 ) and the sector  104  ( 104   1 - 104   12 ) that produced each treatment spot. Each of the two full scans includes a first row created by sequentially scanning sectors  104   1 - 104   6 , followed by a second row created by sequentially scanning sectors  104   7 - 104   12 . 
     Multi-scan-direction scanning element  100  may be configured in any suitable manner. For example, a stair-stepped scanning element (e.g., element  100 C) may be configured for multi-scan-direction scanning Such scanning element may be similar to the stair-stepped scanning element  100 C shown in  FIGS. 17A-17B , but wherein the two sets of sectors  104   1 - 104   6  and  104   7 - 104   12  are configured to generate two offset rows of treatment spots during a single scan (i.e., a single rotation of element  100 ), even when device  10  is held stationary relative to the skin  40 . Like scanning element  100  shown in  FIGS. 17A-17B , each set of sectors  104   1 - 104   6  and  104   7 - 104   12  of the example multi-scan-direction scanning element  100  defines a group of six consecutive ascending steps. However, unlike scanning element  100 C of  FIGS. 17A-17B  in which all 12 reflection surfaces  106  are parallel to each other, for the multi-scan-direction scanning element  100  the reflection surfaces  106   1 - 106   6  of sectors  104   1 - 104   6  are angularly offset from (i.e., non-parallel to) reflection surfaces  106   7 - 106   12  of sectors  104   7 - 104   12 . In other words, reflection surfaces  106   1 - 106   6  of sectors  104   1 - 104   6  are parallel to each other, and reflection surfaces  106   7 - 106   12  of sectors  104   7 - 104   12  are parallel to each other, but the two sets are angularly offset from each other. Thus, reflection surfaces  106   1 - 106   6  generate a first row of six treatment spots, and reflection surfaces  106   7 - 106   12  generate a second row of six treatment spots, offset from the first row. 
     In other embodiments, the multi-scan-direction rotating element may be otherwise configured to deliver beams in any other sequential order along the scan direction, e.g., based on the number and arrangement of sets of sectors  104 , to form a desired two-dimensional array of treatment spots on the skin  40 . Further, any of such multi-scan-direction radiation patterns may be repeated (continuously or non-continuously) while device  10  is moved across the skin  40  in order to form a larger two-dimensional array of treatment spots, e.g., as discussed above with reference to  FIG. 25B . 
     “Constant Deflection” and “Shifting Deflection” Sectors 
     In addition to the various aspects of element  100  and sectors  104  discussed above, in some embodiments, individual sectors  104  may be configured to produce output beams  112  having a constant deflection (angular or translative, depending on the embodiment), or a variable or “shifting” deflection, as that sector  104  rotates through the input beam  110 . 
     Each sector  104  (or least some of the sectors  104 ) of element  100  (e.g., element  100 A,  100 B, or  100 C) may be a “constant angular deflection” sector, which is defined a sector that deflects the input beam  110  such that the angular deflection of the output beam  112  relative to the input beam  110  remains constant or substantially constant as that sector  104  rotates through the input beam  110 . In other words, the angular direction of each output beam  112  remains constant or substantially constant relative to the input beam  110  (and relative to the structure of device  10 ) during the time that each corresponding sector  104  rotates through the input beam  110 . Some embodiments of element  100  (e.g., embodiments of transmissive elements  110 A and  100 B, and certain embodiments of reflective stair-stepped element  100 C) generate an array of constant angular deflection output beams  112  that propagate at constant angles that are different from each other. Other embodiments of element  100  (e.g., certain other embodiments of reflective stair-stepped element  100 C) generate an array of constant angular deflection output beams  112  that are translationally offset from each other, but propagate in the same constant angular direction (i.e., the output beams  112  are parallel to each other). 
     Thus, with constant angular deflection sectors  104 , if device  10  is held stationary relative to the user&#39;s skin, each output beam  112  generated by a respective sector  104  of element dwells at a (different) particular point on the skin  40 . Thus, if device  10  is held stationary relative to the user&#39;s skin, the plurality of constant angular deflection sectors  104  provide a sequentially-delivered series of stationary or substantially stationary treatment spots  70  on the skin, each stationary or substantially stationary treatment spot  70  corresponding to one of the constant angular deflection sectors  104 . 
     However, as discussed above, in at least some embodiments or operational modes, device  10  is designed to be glided across the surface of the skin during operation, in a manner similar to a shaver being glided across the skin. Thus, in a system with constant angular deflection sectors  104 , each output beam  112  moves relative to the skin as device  10  glides across the skin, such that each treatment spot moves relative to the skin, resulting in elongation, “smearing,” or “blurring” in the direction of the gliding. However, despite this smearing of individual treatment spots, sufficient thermal energy may be provided to the treatment spots on a delivered energy per volume basis to provide the desired affect in the skin  40 , at least within a range of operating parameters. For example, the desired effect may be provided as long as the device  10  is not glided across the skin extremely rapidly. Further, some amount of smearing may actually be beneficial for achieving a desired level of delivered energy per volume of irradiated or affected tissue, as a function of selected design and/or operational parameters (e.g., spot size and/or shape, beam intensity, fluence, and/or intensity profile of the delivered output beams, pulse duration and/or frequency, rotational speed of rotating element  100 , etc.). Thus, in certain embodiments, settings, or uses of device  10 , “constant angular deflection” sectors may be used to achieve the desired treatment effects. 
     In some embodiments, smearing caused by gliding may be compensated for, either partially or entirely. For example, the sectors  104  may be configured to be (a) stationary or substantially stationary in the non-glide direction (for which there is no smearing) and (b) to move the beam in the glide direction (for which there is normally smearing) at the same rate or nearly the same rate as the gliding, thereby compensating or partially compensating for smearing. In some embodiments, a glide rate sensor may provide feedback to the user or the device to ensure that the gliding rate is within predefined ranges such that the smearing compensation is effective. 
       FIGS. 26A and 26B  illustrate example treatment spot patterns generated by an element  100  having “constant angular deflection” sectors  104 , in a stamping mode and gliding mode operation of device  10 , respectively. In this example, it is assumed that each output beam  112  delivered to the skin has a circular cross-section. 
       FIG. 26A  illustrates a row of three treatment spots  70  generated by an element  100  having “constant angular deflection” sectors  104 , while device  10  is held stationary with respect to the skin (e.g., with device  10  being operated in a stamping mode). Each output beam  112  dwells over the skin in a stationary or substantially stationary manner as the corresponding constant angular deflection sector  104  rotates through the input beam  110 , such that each resulting treatment spot has a circular shape corresponding to the circular cross-section of the respective output beam  112 . 
       FIG. 26B  illustrates a row of three treatment spots  70  generated by an element  100  having “constant angular deflection” sectors  104 , while device  10  is moved across the surface of the skin (e.g., with device  10  being operated in a manual gliding mode). As shown, each treatment spot is elongated, or smeared, corresponding to the circular cross-section of each respective output beam  112  moving some distance X across the skin in the glide direction during the delivery of that output beam  112  to the skin. The ratio of length L to the width W of each treatment spot  70  is a function of various factors, e.g., the rate of glide of device  10  across the skin, the spot size and/or shape, beam pulse duration, etc. In some embodiments, one or more of such factors may be selected or adjusted in order to produce treatment spots of a predetermined shape or size (or within a predetermined range of shapes or sizes) to provide the desired effect in the tissue. 
     In other embodiments, each sector  104  (or least some of the sectors  104 ) may be a “shifting deflection” sector, which is defined as a sector that deflects the input beam  110  such that the deflection of the output beam  112  relative to the input beam  110  changes or “shifts” either angularly, translationally, or both, in at least one direction (e.g., the scan direction) as that corresponding sector  104  rotates through the input beam  110 . 
     “Shifting deflection” sectors may be used in certain embodiments for achieving a desired level of delivered energy per volume of irradiated or affected tissue, as a function of selected design and/or operational parameters (e.g., beam width, intensity, fluence, and/or intensity profile of the delivered output beams, pulse duration and/or frequency, rotational speed of rotating scanning element  100 , etc.). Thus, in certain embodiments, shifting deflection sectors may be used to achieve the desired treatment effects. 
     Shifting deflection sectors may be configured to shift the deflection of individual output beams  112  directly in the scan direction, or in a direction between the scan direction and the glide direction (such that the shift direction has one vector component along the scan direction and another vector component along the glide direction), or in the glide direction. 
       FIGS. 27A and 27B  illustrate example treatment spot patterns generated by an element  100  having “shifting deflection” sectors  104 , in a stamping mode and gliding mode operation of device  10 , respectively. In this example, it is again assumed that each output beam  112  delivered to the skin has a circular cross-section. 
       FIG. 27A  illustrates a row of three treatment spots  70  generated by an element  100  having “shifting deflection” sectors  104 , while device  10  is held stationary with respect to the skin (e.g., with device  10  being operated in a stamping mode). Although device  10  is held stationary, each MTZ is elongated in the shift direction for a distance Y due to the shifting deflection caused by the specific shape/configuration of the respective sector  104 . In other words, in some embodiments, the “shifting deflection” sectors  104  trace a short line segment or arc rather than dwelling on a spot during that sectors rotation through the incident beam. With reference to  FIG. 27A , in some embodiments, the distance Y of the shift due to the sector optics (apart from any movement of device  10  relative to the skin, e.g., due to gliding) is (a) greater than or equal to the width W of the output beam  112  received at the skin but (b) less than or equal to half the distance of separation S between adjacent treatment spots in the scan direction. In particular embodiments, the distance Y of the shift due to the sector optics is (a) greater than or equal to width W of the output beam  112  but (b) less than or equal to 75% of the distance of separation S between adjacent treatment spots in the scan direction. 
     Further, in some embodiments in which element  100  generates output beams  112  that are angularly offset from each other (e.g., example elements  100 A and  100 B discussed below), in a particular time period during the rotation of a particular sector  104  through the input beam  110 , the angular shift of the output beam  112  caused by that sector  104  (apart from any angular shift due to movement of device  10 , etc.) is less than the angle of rotation of element  100  during that same time period. In more simple terms, the angular shift of the beam caused by a sector  104  is less than the corresponding angular rotation of element  100 , during a particular time period. In some embodiments, the angular shift of the beam caused by a sector  104  is significantly less than the corresponding angular rotation of element  100 , during a particular time period. For example, in some embodiments, the angular shift of the beam caused by a sector  104  is at least 50% less than the corresponding angular rotation of element  100 , during a particular time period. In particular embodiments, the angular shift of the beam caused by a sector  104  is at least 75% less than the corresponding angular rotation of element  100 , during a particular time period. 
       FIG. 27B  illustrates a row of three treatment spots  70  generated by an element  100  having “shifting deflection” sectors  104 , while device  10  is moved across the surface of the skin (e.g., with device  10  being operated in a gliding mode). As shown, each treatment spot is elongated simultaneously in both the deflection shift direction (by a distance Y) and the glide direction (by a distance X), resulting in a generally diagonal elongation. In some embodiments, one or more of such factors may be selected or adjusted in order to produce treatment spots of a predetermined shape or size (or within a predetermined range of shapes or sizes) determined to provide the desired effect in the tissue. 
     In the example shown in  FIGS. 27A and 27B , the shift direction (i.e., the direction of the deflection shift due to the sectors) is in the scan direction. However, the shift direction may be in any other suitable direction, e.g., in the glide direction or any other angular direction. Further, the shift direction may be linear, as in the example shown in  FIGS. 27A and 27B , or non-linear (e.g., tracing an arc or other non-linear path). 
     Radiation Modes 
     Radiation source  14  may generate radiation in any suitable manner relative to time, e.g., continuous wave (CW) radiation, pulsed radiation, or in any other manner relative to time. With respect to embodiments that include a rotating scanning element  100  having a plurality of reflection or deflection sectors (e.g., rotating elements  100 A or  100 B having a plurality of beam-deflecting lenslets, or rotating element  100 C having a plurality of beam-reflection sectors), radiation may be delivered from radiation source  14  to scanning system  48  according to any one or more of the following modes (and/or one or more other modes not covered below), depending on the particular embodiments, device configuration, or device setting of device  10 . 
       FIGS. 28A-28F  illustrate the various radiation modes with respect to an example disc-shaped or cup-shaped rotating element  100 A/ 100 B having four deflecting lenslets  104 A/ 104 B.  FIGS. 29A-29F  illustrate the various modes with respect to an example stair-stepped rotating element  100 C having four reflection sectors  104 C. 
     (1) “Continuous” radiation mode ( FIGS. 28A and 29A ): radiation from radiation source  14  is delivered without interruption to scanning system  48  for a duration equal to or exceeding one full rotation of the rotating scanning element  100  (i.e., a rotation of 360 degrees). Such radiation may be generated as CW radiation (such that the radiation is continuously delivered for any number of multiple rotations of element  100 ), or as pulsed radiation (e.g., where the pulse duration of each pulse corresponds to one full rotation of element  100 , with a pulse-off period between such pulses). 
     (2) “Inter-sector longer pulsed” radiation mode ( FIGS. 28B and 29B ): pulsed radiation is delivered to scanning system  48  such that:
         (a) the duration of individual pulses (i) is greater than or equal to the average duration of individual sectors  104  of the rotating scanning element  100  rotating through a reference point (i.e., a rotation of 360 degrees divided by the number of sectors  104  on the rotating scanning element  100 ), but (ii) less than the duration of one full rotation of the rotating scanning element  100  (i.e., a rotation of 360 degrees), and   (b) individual pulses are incident on multiple sectors  104  of the rotating scanning element  100 ; i.e., individual pulses bridge at least one separation or transition between adjacent sectors  104 .       

     (3) “Inter-sector shorter pulsed” radiation mode ( FIGS. 28C and 29C ): pulsed radiation is delivered to scanning system  48  such that:
         (a) the duration of individual pulses is less than the average duration of individual sectors  104  of the rotating scanning element  100  rotating through a reference point (i.e., a rotation of 360 degrees divided by the number of sectors  104  on the rotating scanning element  100 ), and   (b) individual pulses are incident on multiple sectors  104  of the rotating scanning element  100 ; i.e., individual pulses bridge at least one separation or transition between adjacent sectors  104 .       

     (4) “Intra-sector single pulsed” radiation mode ( FIGS. 28D and 29D ): pulsed radiation is delivered to scanning system  48  such that:
         (a) individual pulses are incident on only one reflection/deflection sector of the rotating scanning element  100 ; i.e., individual pulses do not bridge separations or transitions between adjacent sectors  104 , and   (b) a single pulse is delivered to individual sectors  104  during a revolution of the rotating scanning element  100 .       

     (5) “Intra-sector constant multi-pulsed” radiation mode ( FIGS. 28E and 29E ): radiation from radiation source  14  is delivered to scanning system  48  in a pulsed manner such that:
         (a) multiple pulses are delivered to individual sectors  104  during a revolution of the rotating scanning element  100 , and   (b) the pulse frequency remains constant during a revolution of the rotating scanning element  100 .       

     (6) “Intra-sector non-constant multi-pulsed” radiation mode ( FIGS. 28F and 29F ): pulsed radiation is delivered to scanning system  48  such that:
         (a) multiple pulses are delivered to individual sectors  104  during a revolution of the rotating scanning element  100 , and   (b) the pulse frequency is not constant during a revolution of the rotating scanning element  100 .       

     As mentioned above,  FIGS. 28A-28F  illustrate the various modes with respect to an example disc-shaped or cup-shaped rotating element  100 A/ 100 B having four deflecting lenslets  104 A/ 104 B. 
       FIG. 28A  illustrates a front view of example disc-shaped scanning element  100 A or cup-shaped scanning element  100 B, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to a “continuous” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 A/ 100 B traces a path  230  that extends around the full circumference of element  100 A/ 100 B as element  100 A/ 100 B rotates a full revolution. 
       FIG. 28B  illustrates a front view of example disc-shaped scanning element  100 A or cup-shaped scanning element  100 B, in which radiation is delivered to scanning system  48  according to an “inter-sector longer pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 A/ 100 B is delivered in two pulses  232 A and  232 C during the full rotation of element  100 A/ 100 B, each pulse  232 A and  232 C tracing a path longer than a corresponding arc length of each individual lenslet  104   1 - 104   4 . (Or, in other words, the duration of each pulse  232 A and  232 C is greater than or equal to the average duration of an individual lenslet  104   n  rotating through a reference point (i.e., in this embodiment, a 90 degree rotation of element  100 A/ 100 B). Further, as shown, each pulse  232 A and  232 C crosses over a transition between adjacent lenslets  104 , thus rendering each pulse an “inter-sector” pulse. 
       FIG. 28C  illustrates a front view of example disc-shaped scanning element  100 A or cup-shaped scanning element  100 B, in which radiation is delivered to scanning system  48  according to an “inter-sector shorter pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 A/ 100 B is delivered in two pulses  232 A and  232 C during the full rotation of element  100 A/ 100 B, each pulse  232 A and  232 C tracing a path shorter than a corresponding arc length of each individual lenslet  104   1 - 104   4 . (Or, in other words, the duration of each pulse  232 A and  232 C is less than the average duration of individual lenslet  104  rotating through a reference point (i.e., in this embodiment, a 90 degree rotation of element  100 A/ 100 B). Further, as shown, each pulse  232 A and  232 C crosses over a transition between adjacent lenslets  104 , thus rendering each pulse an “inter-sector” pulse. 
       FIG. 28D  illustrates a front view of example disc-shaped scanning element  100 A or cup-shaped scanning element  100 B, in which radiation is delivered to scanning system  48  according to an “intra-sector single pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 A/ 100 B is delivered in pulses  232 A- 232   d , such that a single pulse is delivered to each lenslet  104   1 - 104   4 , and such that the path traced by each pulse  232 A- 232   d  is located within its corresponding lenslet  104  (i.e., pulse  232 A- 232   d  do not cross over transitions between adjacent lenslets  104 ), thus rendering each pulse an “intra-sector” pulse. 
       FIG. 28E  illustrates a front view of example disc-shaped scanning element  100 A or cup-shaped scanning element  100 B, in which radiation is delivered to scanning system  48  according to an “intra-sector constant multi-pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 A/ 100 B is delivered such that multiple pulses  232  are delivered to each lenslet  104   1 - 104   4  during a revolution of the rotating element  100 A/ 100 B, and such that the pulse frequency remains constant during the revolution of the element  100 A/ 100 B. 
       FIG. 28F  illustrates a front view of example disc-shaped scanning element  100 A or cup-shaped scanning element  100 B, in which radiation is delivered to scanning system  48  according to an “intra-sector non-constant multi-pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 A/ 100 B is delivered such that multiple pulses  232  are delivered to each lenslet  104   1 - 104   4  during a revolution of the rotating element  100 A/ 100 B, but wherein the pulse frequency is not constant during the revolution of the element  100 A/ 100 B. In this example, a three-pulse burst  232 A- 232   c  is delivered to each lenslet  104   1 - 104   4 . 
     As mentioned above,  FIGS. 29A-29F  illustrate the various modes with respect to an example stair-stepped scanning element  100 C having four reflection sectors  104 C that define reflection surfaces  106   1 - 106   4  offset from each other in the direction of the axis A. 
       FIG. 29A  illustrates a front view of example stair-stepped scanning element  100 C, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to a “continuous” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 C traces a path  230  that extends around the full circumference of element  100 C as element  100 C rotates a full revolution. Due to the fact that reflection surfaces  106   1 - 106   4  are offset from each other in the direction of the axis A, the portions of the radiation beam path  230  traced on the different reflection surfaces  106   1 - 106   4  are located at varying distances from the center (i.e., axis A), which should be clear in view of  FIGS. 12-14 . Thus, although path  230  appears to “skip” when crossing the threshold between adjacent reflection surfaces  106   1 - 106   4 , it should be understood that the radiation beam is continuously delivered to element  100 C for the full revolution of element  100 C. 
       FIG. 29B  illustrates a front view of example stair-stepped scanning element  100 C, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to an “inter-sector longer pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 C is delivered in two pulses  232 A and  232 C during the full rotation of element  100 C, each pulse  232 A and  232 C tracing a path longer than a corresponding arc length of each individual reflection surface  106   1 - 106   4 . (Or, in other words, the duration of each pulse  232 A and  232 C is greater than or equal to the average duration of individual reflection surface  106   1 - 106   4  rotating through a reference point (i.e., in this embodiment, a 90 degree rotation of element  100 C). Further, as shown, each pulse  232 A and  232 C crosses over a transition between adjacent reflection surface  106   1 - 106   4 , thus rendering each pulse an “inter-sector” pulse. 
       FIG. 29C  illustrates a front view of example stair-stepped scanning element  100 C, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to an “inter-sector shorter pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 C is delivered in two pulses  232 A and  232 C during the full rotation of element  100 C, each pulse  232 A and  232 C tracing a path shorter than a corresponding arc length of each individual reflection surface  106   1 - 106   4 . (Or, in other words, the duration of each pulse  232 A and  232 C is less than the average duration of individual reflection surface  106   1 - 106   4  rotating through a reference point (i.e., in this embodiment, a 90 degree rotation of element  100 C). Further, as shown, each pulse  232 A and  232 C crosses over a transition between adjacent reflection surface  106   1 - 106   4 , thus rendering each pulse an “inter-sector” pulse. 
       FIG. 29D  illustrates a front view of example stair-stepped scanning element  100 C, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to an “intra-sector single pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 C is delivered in pulses  232 A- 232   d , such that a single pulse is delivered to each reflection surface  106   1 - 106   4 , and such that the path traced by each pulse  232 A- 232   d  is located within its corresponding reflection surface  106   1 - 106   4  (i.e., pulse  232 A- 232   d  do not cross over transitions between adjacent reflection surface  106   1 - 106   4 ), thus rendering each pulse an “intra-sector” pulse. 
       FIG. 29E  illustrates a front view of example stair-stepped scanning element  100 C, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to an “intra-sector constant multi-pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 C is delivered such that multiple pulses  232  are delivered to each reflection surface  106   1 - 106   4  during a revolution of the rotating element  100 C, and such that the pulse frequency remains constant during the revolution of the element  100 C. 
       FIG. 29F  illustrates a front view of example stair-stepped scanning element  100 C, viewed along the rotation axis A, in which radiation is delivered to scanning system  48  according to an “intra-sector non-constant multi-pulsed” radiation mode, according to an example embodiment. As shown, the radiation beam incident on rotating element  100 C is delivered such that multiple pulses  232  are delivered to each reflection surface  106   1 - 106   4  during a revolution of the rotating element  100 C, but wherein the pulse frequency is not constant during the revolution of the element  100 C. In this example, a three-pulse burst  232 A- 232   c  is delivered to each reflection surface  106   1 - 106   4 . 
     Any of the radiation modes may continue uninterrupted for (a) less than a full rotation of the rotating scanning element  100  (except for continuous mode, which requires uninterrupted delivery of radiation for at least one full rotation), (b) one full rotation of the rotating scanning element  100 , or (c) multiple rotations of the rotating scanning element  100 . 
     For example, the current radiation mode may be interrupted after each full rotation of the rotating scanning element  100 . As another example, the current radiation mode may be interrupted after a predetermined number of rotations of the rotating scanning element  100 , after a predetermined time, or after a predetermined amount of radiation has been delivered to the skin  40 , for example. In some embodiments, the current radiation mode may be interrupted and/or started or re-started in response to feedback from one or more systems of device  10 , e.g., immediately (i.e., in the middle of a particular rotation of element  100 /scan of input beam  110 ), at the end of the current rotation of element  100 /scan of input beam  110 , or in any other manner. For example, as discussed in greater detail below with respect to  FIG. 38-46 , the current radiation mode may be interrupted and/or started or re-started in response to:
         (a) signals from one or more skin contact sensors  204  indicating whether application end  42  of device  10  is in contact with the skin;   (b) signals from displacement monitoring and control system  132 , e.g., indicating the distance that device  10  has moved across the skin  40 ;   (c) signals from usability control system  133 , e.g., indicating whether device  10  is in contact with the skin and experiencing a sufficient displacement or speed across the skin (e.g., based on signals from one or more displacements sensors  20  and skin contact sensors  204 );   (d) signals from one or more sensors  26  or safety systems indicating a potentially unsafe condition; and/or   (e) any other suitable automated feedback.       

     Further, in some embodiments or settings, the current radiation mode may be interrupted manually via a user interface  28 , e.g., in response to the user pressing a button, releasing a button, or moving the device  10  away from contact with the skin  40 . 
     An “interruption” of the current radiation mode may include any of (a) interrupting delivery of radiation to the skin  40  (e.g., by turning off the treatment radiation source  14 , or preventing the radiation from being output from device  10 , by blocking or redirecting the radiation within device  10 ), (b) switching to a different radiation mode, and (c) modifying one or more parameters of the delivered radiation, including fluence, power density, wavelength, pulse frequency, duty rate, pulse on time (pulse width), pulse off time, treatment spot size and/or shape, outlet beam focal plane, etc. 
     The duration of an interruption of the current radiation mode (before continuing radiation delivery) may be a predetermined time, a predetermined rotation of the rotating scanning element  100  (e.g., to skip or bypass a specific number of reflection sectors), or may be determined based on feedback from one or more systems of device  10 . For example, as discussed in greater detail below with respect to  FIG. 46 , after an interruption of a particular radiation mode in response to signals from displacement monitoring and control system  132  or usability control system  133  (e.g., indicating that device  10  is not in contact with the skin or has not moved a threshold distance across the skin  40 ), the particular radiation mode may be continued in response to further signals from displacement monitoring and control system  132  or usability control system  133  (e.g., indicating that device  10  is back in contact with the skin and/or has moved the threshold distance across the skin  40 ). 
     In the example embodiments shown in  FIGS. 28A-28F and 29A-29F , each example scanning elements  100  includes four reflection sectors  104 . It should be understood that the illustrated embodiments are merely examples, for illustrative purposes. As discussed above, rotating element  100  may include any number of reflection sectors  104 . For example, in some embodiments, rotating element  100  includes about 6 reflection sectors  104 , or about 10-12 reflection sectors  104 , or between 15-20 reflection sectors  104 , more than 20 reflection sectors  104 , or any other suitable number of reflection sectors  104 . 
     Further, in the example embodiments shown in  FIGS. 28A-28F and 29A-29F   1 , as well as those shown in  FIGS. 7, 8, and 13 , the reflection sectors  104  extend the same distance around the respective scanning element  100  (e.g., in the four-sector scanning elements  100  shown in  FIGS. 28A-28F and 29A-29F , each reflection sector  104  extends 90 degrees around the respective rotating element  100 , and in the 12-sector scanning elements  100  shown in  FIGS. 7 and 8 , each reflection sector  104  extends 30 degrees around the respective rotating element  100 ). Again, it should be understood that the illustrated embodiments are merely examples, for illustrative purposes. The reflection sectors  104  of any particular scanning element  100  may or may not extend the same distance or angle around the element  100 . Thus, scanning element  100  may include n reflection sectors  104 , each extending 360/n degrees around element  100 ; or alternatively, one or more of the n reflection sectors  104  may extend more or less than 360/n degrees around element  100 . In some embodiments, the n reflection sectors  104  may extend x i  degrees around scanning element  100 , where the series x i , x i+1 , . . . x n−1 , x n  increases linearly, according to an n th  order equation, or other non-linear equation. For example,  FIG. 30  illustrates a scanning element  100  with six deflection sectors  104 C 1 - 104 C 6 , which extend 10 degrees, 30 degrees, 110 degrees, 170 degrees, 90 degrees, and 110 degrees, respectively, around element  100 . 
     Use of Non-Propagating Areas to Provide Constant-Input/Pulsed-Output Effect 
     In some embodiments, adjacent reflection sectors  104  and/or reflection surfaces  106  may be separated from each other by areas that do not reflect input beam  110  for propagation toward the skin  40 , such areas including non-reflective areas, or areas that reflect or deflect input beam  110  away from propagation toward the skin  40 , for example. Such areas are referred to herein as “non-propagating areas.” In some embodiments, non-propagating areas may be used to sample the treatment beam, such as to measure its power or energy with a photodiode, or for other purposes. In some embodiments, non-propagating areas may be used to control the duration or pulse width of individual output beams  112  to be delivered to the skin  40 . For example, an input beam  110  may be delivered uninterrupted for a time period that spans the rotation of multiple reflection sectors  104  through the input beam  110 . By including non-propagating areas between adjacent reflection surfaces  106 , the uninterrupted input beam  110  may be effectively converted into a pulsed array of output beams  112 . Such effect is referred to herein as a “constant-input/pulsed-output” effect. The relative size and shape of the reflection surfaces  106  and non-propagating areas may define at least in part the effective pulse-on time (i.e., pulse width) of each output beam  112 , as well as the pulse-off time between output beams  112 , and thus a pulse duty cycle. 
       FIG. 31  illustrates an end view, taken along the axis of rotation A, of an example rotating scanning element  100  (e.g., element  100 A,  100 B, or  100 C) having four deflection sectors  104  separated by four non-propagating areas  240 , according to an example embodiment. 
     An input beam  110  may be delivered uninterrupted for a time period that spans the rotation of multiple deflection sectors  104  (e.g., lenslets or mirrored sectors) through the input beam  110 . Input beam  110  is incident to deflection sectors  104  and non-propagating areas  240  in an alternating manner. Each deflection sector  104  creates an output beam  112  defining a pulse-on time (pulse width), and each non-propagating areas  240  creates an interruption defining a pulse-off time between consecutive pulses. In this manner, a “constant-input/pulsed-output” effect can be generated. The pulse-on time (i.e., pulse width) of each output beam  112 , and the pulse-off time between output beams  112 , and thus the pulse duty cycle, may be defined by (a) the relative size and shape of the deflection sectors  104  and non-propagating areas  240 , defined in the illustrated example by the respective path lengths PL R  and PL NP  traced by input beam  110  as element  100 C rotates about axis A, and (b) the rotational speed of element  100 C. The relative size and shape of the deflection sectors  104  and non-propagating areas  240  may be selected to provide any desired pulse-on time and pulse-off time, for a given rotational speed of element  100 C. 
     In the illustrated example, the four deflection sectors  104  have the same shape and size, and the four non-propagating areas  240  have the same shape and size, such that the pulse-on time and pulse-off time is the same for each output beam  112 , assuming a constant rotational speed of element  100 C. In other embodiments, the different deflection sectors  104  may have different sizes and/or shapes, and/or the different non-propagating areas  240  may be may have different sizes and/or shapes, such that the pulse-on time for different output beams  112  and/or the pulse-off time between different output beams  112  may vary as desired. 
     The use of non-propagating areas  240  may be combined in any suitable manner with any radiation mode, e.g., any of the various continuous or pulsed radiation modes discussed above with reference to  FIGS. 28A-28F and 29A-29F , in order to control one or more parameters of beams delivered to the skin  40 . 
     On-Axis Vs. Off-Axis Output Beams; Optional Downstream Optics 
     A scanned array of beams may include “off-axis” and “on-axis” beams. “Off-axis” output beams  112  are output beams  112  in an array that have been deflected (by respective lenslets  104 ) by a relatively large amount, in contrast to “on-axis” output beams that have been deflected (by respective lenslets  104 ) by a relatively small amount or even not deflected at all. In some embodiments, the central output beam or beams  112  of an array are considered on-axis, while outer beams are of the array are considered off-axis. For example, in the examples arrangements shown in  FIGS. 10A and 11A , output beam  112 B is considered on-axis, while output beams  112 A and  112 C are considered off-axis. 
     The deflection of individual output beams  112  caused by lenslets  104  may affect the beam intensity profile of such beams. Generally, the greater the deflection, the greater the influence on the beam intensity profile. Thus, the beam intensity profiles of off-axis beams are generally influenced more than the profiles for on-axis beams. For example, off-axis output beams  112  of an array may have a defocused or widened intensity profile in at least one direction or axis, as compared to on-axis beams  112  in the same array, due to the deflection of such off-axis output beams  112  by the respective sectors  104  of element  100 . 
       FIGS. 32 and 33  illustrate example intensity profiles of output beams  112 , measured at the surface of the skin, for an on-axis output beam  112  and an off-axis output beam  112 , respectively. For example, with reference to the arrangements shown in  FIGS. 18 and 20 ,  FIG. 32  may generally represent the beam intensity profile for on-axis output beam  112 B, while  FIG. 33  may represent the beam intensity profile for off-axis output beams  112 A or  112 C. 
     As shown, the intensity profile of the on-axis beam  112  is narrower in at least one direction (in this example, the fast axis direction), and may have a higher intensity peak (or peaks) as compared to the intensity profile of the off-axis beam  112 . In some embodiments, the intensity profile of the on-axis beam  112  may also be narrower in the orthogonal direction (in this example, the slow axis direction) as compared to the off-axis beam  112 . 
       FIG. 34  illustrates a graph  130  of the fraction of the energy delivered to a target surface that is delivered within a square of a defined size on that target surface. The energy delivered within the square is referred to as the “ensquared energy.” Graph  130  shows the fraction of ensquared energy as a function of square size, for an example on-axis beam (e.g., as shown in  FIG. 32 ) and an example off-axis beam (e.g., as shown in  FIG. 33 ). The square size is defined in terms of half width from a centroid of the intensity profile plane, e.g., points C indicated in the intensity profile plane shown in  FIGS. 32 and 33 . Thus, a half width of 50 μm in graph  130  refers to a 100 μm×100 μm square centered around centroid C. 
     As shown in graph  130 , for small half widths (i.e., smaller squares), the ensquared energy for the on-axis beam is higher than that of the off-axis beam. For example, at a half width of 50 μm, the fraction of ensquared energy for the on-axis beam is about 0.43, compared to about 0.40 for the off-axis beam. However, for larger half widths (i.e., larger squares), the ensquared energy for the on-axis beam is similar to that of the off-axis beam (and in fact, may be smaller than that of the off-axis beam for certain half width). In one embodiment, an treatment spot diameter or width of about 0.2 mm (200 μm) is desired. The dashed line in graph  130  at 100 μm half width corresponds to a square width of 0.2 mm (200 μm). As shown, the ensquared energy for at that dimension is approximately the same for the on-axis beam and the off-axis beam. Thus, despite the defocused and/or widened intensity profile of the off-axis beam (as compared to the on-axis beam), the total energy delivered to an treatment spot of about 0.2 mm (200 μm) in width or diameter is about the same for both on-axis and off-axis beams in the same scanned array for this embodiment. Thus, the desired effect may be provided without needing further treatment optics to act on the off-axis beams. 
     The shape of the intensity profile of each output beam  112  along each axis (e.g., along the slow axis and fast axis for asymmetric profile beams, e.g., as generated by laser diodes) is determined at least by the type of treatment radiation source  14  and the particular elements of optical system  15 . Thus, different embodiments may provide any of a variety of intensity profiles at the target plane (e.g., the surface of this skin) in any particular axis. Examples of such intensity profiles include, e.g., Gaussian, pseudo-Gaussian, flat-topped, pseudo-flat-topped, etc., and may include a single peak, two peaks, more than two peaks, or no significant peaks (e.g., flat-topped). 
     In some embodiments, one or more downstream optical elements  60 B (e.g., with reference to  FIG. 3C ). Some example downstream optics  60 B include: (a) downstream fast axis optic  64 ′ (e.g., cylindrical lens) for focusing, aberration correction, and/or imaging and/or treatment of output beams  112 , e.g., as discussed above with reference to  FIGS. 10A-10B and 11A-11B ; (b) mirrors  150 A- 150 C for deflecting output beams  112 , and (c) path length compensation elements  152  for providing equal total path lengths for output beam  112  generated by a stair-stepped scanning element  100 C. 
     Downstream optics  60 B may include any one or more planar mirrors, optically-powered lenses or mirrors, or other optical elements (as defined above) that influence output beams  112 . Downstream optics  60 B may be provided for a variety of purposes, e.g., to deflect one or more output beams  112  such that they are incident to the target surface at a desired angle (e.g., substantially normal to the target surface); to influence the focus of one or more output beams  112  (e.g., to provide a desired focal point or focal plane relative to the target surface); to influence the beam intensity profile of one or more output beams  112  at the focal point or focal plane of output beams  112 ; or for any other purpose. 
     For example, downstream fast axis optic  64 ′, e.g., as shown in  FIGS. 10 and 11 , may be provided downstream of scanning system  48  for refocusing or reimaging or controlling or adjusting the intensity profile of output beams  112  as desired. In some embodiments, such downstream optics  60 B may be particularly provided for refocusing or treating off-axis output beams  112 , as such output beams  112  may have defocused and/or widened intensity profiles or otherwise different properties as compared to on-axis beams  112 , as discussed above. For example, such downstream optics  60 B may be provided for narrowing the intensity profile of off-axis output beams  112  along at least one axis. For instance, fast axis optic  64 ′ shown in  FIGS. 10 and 11 , which may comprise, e.g., a rod lens, aspheric lens, or any other suitable optical element, may be provided to refocus or narrow the intensity profile of off-axis beams  112  in the fast axis direction. In some embodiments, such downstream optics  60 B may be used to deliver a beam intensity profile to the skin that produces the desired effects in the tissue. In other embodiments, beam intensity profiles sufficient to provide the desired effects in the skin are provided without such downstream optics  60 B (e.g., without fast axis optic  64 ′). For example, in some embodiments that utilize a laser diode, beam intensity profiles sufficient to provide the desired effects in the skin are provided using only a single fast axis optical element (e.g., a rod lens or aspheric lens) and a scanning element that both scans the beam and treats the beam in the slow axis direction. 
     Other embodiments of device  10  may include no downstream optics  60 B. In some embodiments, the only element along the downstream beam path is a window  44  at the application end  42  that may comprise a clear glass or plastic film, plate, layer, or block. A window  44  may be provided to protect the internal components of device  10 , as discussed above, or it could also be a spectral filter to allow only the treatment beam to pass through and provide the desired cosmetic visual effect. Output beams  112  may travel from scanning optics  62  through a chamber within housing  24 , though window  44 , and to the skin  40 , with no optics  60 B downstream of scanning optics  62 . The chamber may be sealed and filled with air or other gas, or may comprise a vacuum. Alternatively the chamber may be open to ambient air, e.g., through one or more openings in housing  24  (e.g., to encourage heat transfer away from device  10 ). As another example, device  10  may include an open aperture, rather than window  44 , in the application end  42 , such that output beams  112  travel from scanning optics  62  through an open-air chamber and out through the aperture in application end  42 , without being influenced by any downstream optics  60 B or passing through any window or other element. 
     Radiation Engine 
     As discussed above, radiation engine  12  may include any number and or type(s) of radiation sources  14  configured to generate radiation to be delivered to the skin  40 . For example, radiation sources  14  may include one or more laser diode, fiber laser, VCSEL (Vertical Cavity Surface Emitting Laser), LED, etc. Thus, depending on the particular type(s) of radiation source(s)  14  used, the radiation may have different properties, such as the radiation propagated by each treatment radiation source  14  may be symmetric about all axes, i.e., axis-symmetric (e.g., radiation produced by a fiber laser), or asymmetric about different axes, i.e., axis-asymmetric (e.g., radiation produced by a laser diode). 
       FIGS. 33A and 33B  illustrate an example embodiment of a radiation engine  12  that includes a laser diode as the radiation source  14 . In this example, radiation engine  12  includes a laser package  250  (which includes the laser diode  14 ), a heat sink  36 , a laser package securing system  252 , and a lens securing system  254  for securing a fast axis optic  64  (in this embodiment, a cylindrical lens) relative to the laser diode  14 .  FIG. 33A  illustrates a full view of radiation engine  12 , and  FIG. 33B  is a magnified view of a portion of radiation engine  12  illustrating the particular arrangement of laser package  250  (which includes the laser diode  14 ), laser package securing system  252 , and lens securing system  254  for securing fast axis lens  64 . Fast axis lens  64  is not shown in  FIG. 33A , for illustrative purposes only. 
     In the illustrated embodiment, radiation source  14  is a single-emitter or multi-emitter laser diode  14  provided on a laser package  250 . Laser package  250  may be, for example, a Q-Mount or B-Mount laser package, which may be particularly suitable for use with the illustrated example lens mounting system. However, other laser packages well suited for use with such lens mounting features include flat ceramic type packages and C-Mount packages and custom packages, among others. Other embodiments include any other suitable type(s) of radiation sources, e.g., other type(s) of laser sources (e.g., one or more laser diode bars, VCSELs, etc.) or any other type(s) of radiation sources. 
     As shown in  FIG. 33A , laser diode  14  may be electrically coupled to a printed circuit board (PCB)  258  in any suitable manner. For example, laser diode  14  may be coupled to electronics on PCB  258  by an electrical connection  266 , e.g., a flexible cable. 
     Laser diode  14  of the illustrated embodiment includes a single emitter that may include an emitting edge or surface  256 , from which a beam  108  is emitted. In one embodiment, emitting edge/surface  256  is approximately 100 μm by 1 μm, extending lengthwise in the x-axis direction. In other embodiments, laser  14  may include multiple emitters or emitting edges/surfaces  256 . 
     Heat sink  36  serves to cool the laser  14  and may be fabricated via an extrusion process or in any other suitable manner. Some embodiments include one or more fans to help maintain the laser temperature at a desired level. Heat sink  36  may include fins or other structures for promoting heat transfer. In some embodiments heat sink  36  may be passive and/or absorb and/or transfer heat by conduction only and/or combined with natural convection and/or combined with radiative heat transfer. In some embodiments, heat sink  36  in the fully assembled device  10  has a rating of about 2.5° C./W or lower. In particular embodiments, heat sink  36  in the fully assembled device  10  has a rating of about 1.5° C./W or lower. 
     In some embodiments, laser diode  14  also includes one or more fans  34  to actively cool heat sink  36 , to further promote heat transfer from laser diode  14  and/or other powered components of device  10 . 
     Laser package securing system  252  may comprise any devices used to secure laser diode package  24  to heat sink  36 , e.g., via soldering, clamping, spring forces, or using thermally conductive adhesive. A bottom surface of laser package  250  may contact heat sink  36  either directly, or using thermal interface material (e.g., thermal grease), to promote heat transfer into heat sink  36 . 
     Laser package  250  may include one or more laser diodes  14  directly mounted to heat sink  36  via suitable means (e.g., via soldering, clamping, or adhesive) or mounted to one or more subcarriers (e.g., a ceramic, plated ceramic, copper block, etc) to provide, among other things, electrical isolation and/or thermal conduction. Electrical connection to the laser diode emitter(s) may be made by wire bonding, clamping, or other suitable means between the emitter(s) and the subcarrier(s), to heat sink  36 , or to other electrical connection point(s) (e.g., printed circuit board  258 ) in the device  10 . Some example arrangements for mounting a laser diode  14  to heat sink  36  are shown in the embodiments of  FIGS. 36 and 37 , which are discussed below. 
     In the illustrated embodiment, laser package securing system  252  includes a clip  260  which is secured to heat sink  36  by a screw  262 , in order to secure laser package  250  to heat sink  36 . Mounting features may also be provided in heat sink  36  to assure repeatable positioning of the laser assembly. The laser mounting features may be modified to accommodate a variety of standard industry laser packages. Example embodiments of laser package securing system  252  that do not require a clip or screw are discussed below with reference to  FIGS. 34-37 . 
     Lens securing system  254  in this embodiment is configured for securing a fast axis lens  64  to heat sink  36 , in order to secure fast axis lens  64  in a fixed position relative to laser diode  14 . The beam  108  emitted by laser diode  14  may have a relatively large angular divergence in the fast axis (indicated as the y-axis in  FIG. 33B ). Thus, a high-numerical-aperture (high NA) short-focal-length cylindrical lens (or “rod lens”)  64  may be provided to reduce the angular divergence of the fast axis profile of beam  108 . Due to its high NA, the exact positioning of cylindrical lens  64  relative to laser diode  14  may be relatively important. In one embodiment, cylindrical lens  64  is about 12 mm long with a diameter of about 2 mm. However, lens  64  may have any other suitable dimensions. Further, in other embodiments, lens  64  may comprise a different shaped lens. For example, lens  64  may be an aspheric lens or a spherical lens. 
     Lenses are commonly attached to other structures using UV curing epoxy. However, UV curing epoxy experiences shrinkage during the curing process, which changes the position of the lens relative to the laser, which may negatively affect the desired beam output characteristics. Thus, lens securing system  254  may be configured for mounting fast axis optic  64  to heat sink  36  in a manner that minimizes or reduces the movement of optic  64  relative to laser diode  14 , including during the mounting process, e.g., during a UV curing process. 
     In the illustrated embodiment, lens securing system  254  comprises a pair of lens support structures  270  and  272  that extend in the z-axis direction from a side of heat sink  36 . Structures  270  and  272  may be formed integral with heat sink  36 . Structures  270  and  272  extend past the front edge of laser package  250  in the z-axis direction, and may be separated by a distance of 1.5× to 2× the width of laser package  250  in the x-axis direction. The geometry of structures  270  and  272  may be at least partially generated in the heat sink extrusion direction, which may minimize or reduce the number of components and/or amount of post machining required, thus reduce the cost of the assembly. 
     In some embodiments, heat sink  36  and lens support structures  270  and  272  may be formed integrally by a single extrusion process, followed by a machining process to form an extended mounting portion  274  that includes support structures  270  and  272 . In addition, locating features  278  for the laser package  250  may also be machined into the heat sink  36 . Forming heat sink  36 , lens support structures  270  and  272 , and locating features  278  integrally creates a robust structure between the laser  14  and lens  64 . In other embodiments, heat sink  36  may be formed by die-casting, forging, and/or any other suitable manufacturing process or processes. 
     As shown in  FIG. 33B , high NA cylindrical lens  64  is mounted between support structures  270  and  272 . Lens  64  may be secured to support structures  270  and  272  in any suitable manner. For example, lens  64  may be positioned between structures  270  and  272  and adhered to structures  270  and  272  using UV adhesive  276 , e.g., UV epoxy  276  that is cured via a UV curing process. 
     To mount the lens  64 , a small amount of UV adhesive  276  is applied to the ends of the lens  64  and/or to the inside surfaces of lens support structures  270  and  272 . Lens  64  is then positioned between support structures  270  and  272 , with a small space between each end of lens  64  and the respective support structure  270  and  272 . Surface tension may hold the adhesive  276  in place while positioning lens  64  in between support structures  270  and  272 . Alignment tool(s) and method(s), such as real time monitoring of the beam during the mounting of lens  64 , may be used. Once in the proper location, the adhesive  276  wets to the lens support structures  270  and  272  and spans the gap between the support structures  270  and  272  and ends of lens  64 . The adhesive  276  is then cured using a high intensity UV radiation source. 
     During curing, shrinkage of the epoxy may cause lens  64  to move in the x-axis direction, as lens  64  and support structures  270  and  272  are aligned in the x-axis direction. However, because cylindrical lens  64  has no optical power in the x-axis, movement of lens  64  in the x-axis does not substantially change the desired beam characteristics after the real time alignment of the lens  64  relative to the laser diode  14 . 
     Cylindrical lens  64  may be positioned at any suitable distance from the laser emitting edge/surface  256 . In one example embodiment, lens  64  is positioned about 260 um from the laser emitting edge/surface  256 . 
     In some embodiments, radiation engine  12  formed or configured as discussed above may provide one or more advantages, as compared to certain known radiation engines. For example, using a single structure (heat sink  36 ) for cooling, alignment, and lens mounting features may be advantageous, e.g., for structural integrity, heat transfer, compactness, reducing the number of components, and/or reducing costs. As another example, the radiation engine  12  discussed above may minimize or reduce the required machining of parts. As another example, the radiation engine  12  discussed above may not require tight tolerances on lens support structures  270  and  272 . As another example, the radiation engine  12  discussed above may allow for epoxy shrinkage without significantly affecting the resulting beam characteristics. As another example, the radiation engine  12  discussed above may allow for ease of adhesive application on either the lens or lens mounting features. 
       FIG. 34  illustrate another example configuration of a radiation engine  12 . In this embodiment, laser package  250  and fast axis optic  64  are positioned within a recess  282  defined in heat sink  36 . This may allow similar and/or additional benefits than the embodiment shown in  FIG. 35 , such as further reduction in number of components or greater structural integrity, among others. The embodiment of  FIG. 34  also includes a pair of metal connector  267  between printed circuit board  258  and laser package  250  to provide an electrical path through laser diode  14 . Each connector  267  may be mechanically-loaded to make good contact with the relevant portions of laser package  250  (e.g., using springs, flexures, bent tabs, etc.). This may provide a number of advantages included not requiring a soldered connection, connectors, pigtails, or flying leads. 
       FIGS. 35A and 35B  illustrate another example configuration of a radiation engine  12 .  FIG. 35A  shows a full view of radiation engine  12 , while  FIG. 35B  is a zoomed-in view of the arrangement of laser package  250 . Similar to the embodiment of  FIG. 34 , in this embodiment, laser package  250  and fast axis optic  64  are positioned within a recess  282  defined in heat sink  36 . Laser package  250  is secured to heat sink  36  by a pair of connection elements  267  extending from a bottom surface of printed circuit board  258 , to provide an electrical path between PCB  258  and laser diode  14 . Each connection element  267  includes a mechanically-loaded or spring-biased element  268  to ensure good contact with relevant contact portions of laser package  250 , and to provide a downward securing force to secure laser package  250  to heat sink  36 . 
       FIGS. 36A-36C  illustrate one embodiment of a laser package  250 A that may be used, e.g., in any of the example radiation engines  12  disclosed herein. As shown, laser package  250 A includes a diode laser  14  mounted on a thermally and electrically conductive submount  284  (e.g., a copper block), which may be configured for mounting to heat sink  36 . Laser package  250 A also includes an electrically insulative contact pad  286  (e.g., formed from ceramic or other electrically insulative material) mounted to submount  284 , which insulative contact pad  286  may include a metalized or otherwise electrically conductive top surface  290 . Diode laser  14  may be electrically connected to the conductive top surface  290  of contact pad  286  by a number of connectors  288  (e.g., wire bonds). 
     Connection elements  267 A and  267 B may be provided to electrically couple laser package  250 A (in particular, laser diode  14 ) to printed circuit board  258 . In particular, connection element  267 A may contact conductive top surface  290  of contact pad  286  (e.g., via a mechanically-loaded or spring-biased element  268 ) and connection element  267 B may contact a top surface of conductive submount  284  (e.g., via a mechanically-loaded or spring-biased element  268 ), thus establishing a conductive path from PCB  258  through connection element  267 A, conductive surface  290 , connectors (e.g., wire bonds)  288 , laser diode  14 , conductive submount  284 , connection element  267 B, and back to PCB  258 . 
     Submount  284  may be coupled to heat sink  36  either directly, or using thermal interface material  296  (e.g., thermal grease), to promote heat transfer into heat sink  36 . Submount  284  may be secured to heat sink  36  in any suitable manner, e.g., via UV-cured epoxy  298 . 
       FIG. 37  illustrates another example embodiment of a laser package  250 B that may be used, e.g., in any of the example radiation engines  12  disclosed herein. As shown, laser package  250 B includes a diode laser  14  mounted on an electrically insulative contact pad  286  (e.g., formed from ceramic or other electrically insulative material), which is in turn mounted to heat sink  36 . A top surface of electrically insulative contact pad  286  includes first and second conductive area  290 A and  290 B having a metalized or otherwise electrically conductive top coating or surface, which are separated from each other by a non-conductive area  291  that is not metalized or otherwise electrically conductive. As shown, conductive connectors (e.g., wire bonds)  288  connect first conductive area  290 A with laser diode  14 , which is mounted on second conductive area  290 B. 
     Connection elements  267 A and  267 B may be provided to electrically couple laser package  250 A (in particular, laser diode  14 ) to a printed circuit board  258 . In particular, connection element  267 A may contact first conductive area  290 A on the top surface of contact pad  286  (e.g., via a mechanically-loaded or spring-biased element  268 ) and connection element  267 B may contact second conductive area  290 B on the top surface of contact pad  286  (e.g., via a mechanically-loaded or spring-biased element  268 ), thus establishing a conductive path from PCB  258  through connection element  267 A, first conductive area  290 A, connectors (e.g., wire bonds)  288 , laser diode  14 , second conductive area  290 B, connection element  267 B, and back to PCB  258 . 
     Contact pad  286  may be coupled to heat sink  36  either directly, or using thermal interface material  296  (e.g., thermal grease) to promote heat transfer into heat sink  36 . Contact pad  286  may be secured to heat sink  36  in any suitable manner, e.g., via UV-cured epoxy  298 . 
     Displacement-Based Control 
     As discussed above regarding  FIG. 1 , device  10  may include control system  18  configured to control various controllable operational parameters of device  10  (e.g., operational aspects of radiation source  14 , scanning system  48 , etc.). In some embodiments, control system  18  may include a displacement-based control system  132  configured to determine the displacement of device  10  relative to the skin as device  10  is moved across the surface of the skin (e.g., while operating device  10  in a gliding mode or a stamping mode), and control one or more controllable operational parameters of device  10  based on the determined displacement of device  10 . For example, displacement-based control system  132  may control the one or more operational aspects radiation source(s)  14 , such as for example, controlling the radiation mode of radiation source(s)  14 , controlling the on/off status of radiation source(s)  14 , controlling the timing of such on/off status (e.g., pulse trigger delay, pulse duration, pulse duty cycle, pulse frequency, temporal pulse pattern, etc.), controlling parameters of the radiation (e.g., wavelength, intensity, power, fluence, etc.), controlling parameters of optics  16 , controlling parameters of beam scanning system  48  (e.g., controlling the on/off status, rotational speed, direction of rotation, or other parameters of motor  120 ), and/or any other controllable operational parameters of device  10 . 
     In some embodiments, displacement-based control system  132  may also provide feedback to the user via a display  32  and/or one or more other user interfaces  28  based on (a) the monitored displacement of device  10  and/or (b) the automatic control of one or more controllable operational parameters by system  132 . For example, system  132  may provide audio, visual, and/or tactile feedback to the user indicating data detected, or actions taken, by system  132 , e.g., feedback indicating whether or not the displacement of device  10  exceeds a predetermined threshold distance, feedback indicating that treatment radiation source  14  or scanning system  48  (e.g., motor  120 ) has been turned on or off, feedback indicating that system  132  has automatically changed the radiation mode or other parameter of treatment radiation source  14 , etc. 
     Displacement-based control system  132  may include, utilize, or otherwise cooperate with or communicate with any one or more of the control subsystems  52  discussed above with respect to  FIG. 2  (e.g., radiation source control system  128 , scanning system control system  132 , usability control system  133 , and user interface control system  134 , including user interface sensor control subsystem  140  and user input/feedback control subsystem  142 ), as well as control electronics  30 , any one or more sensors  26 , user interfaces  28 , and displays  32 . 
       FIG. 38  illustrates a block diagram of a displacement-based control system  132 , according to certain embodiments. As shown, displacement-based control system  132  includes a displacement sensor  200 , control electronics  30 , and one or more of: treatment radiation source  14 , scanning system  48 , and display  32 . In discussing various radiation-based sensors  26 , radiation source  14  is referred to as “treatment radiation source  14 ” to distinguish from any radiation source of the particular sensor  26 . In general, displacement sensor  200  collects data regarding the displacement of device  10  relative to the skin  40  and communicates such data to control electronics  30 , which analyzes the data and controls or provides feedback via one or more of treatment radiation source  14 , scanning system  48 , and display  32 . In some embodiments, control electronics  30  may also analyze particular user input received via one or more user interfaces  28  in conjunction with data received from sensor  200 . For example, the appropriate control or feedback provided by control electronics  30  (e.g., as defined by a relevant algorithm  148 ) may depend on the current operational mode and/or other settings selected by the user. For instance, the minimum threshold displacement for triggering particular responses by control electronics  30  may depend on the current operational mode selected by the user. 
     Control electronics  30  may include any suitable logic instructions or algorithms  154  stored in memory  152  and executable by one or more processors  150  (e.g., as discussed above regarding  FIG. 2 ) for performing the various functions of displacement-based control system  132 . Displacement sensor  200  may be configured for detecting, measuring, and/or calculating the displacement of device  10  relative to the skin  40 , or for generating and communicating signals to control electronics  30  for determining the displacement of device  10 . In some embodiments, e.g., as discussed below with reference to  FIGS. 40-43 , displacement sensor  200  may be a single-pixel sensor configured to identify and count intrinsic skin features in the skin, and determine a displacement of the device  10  across the skin based on the number of identified intrinsic skin features. As used herein, “intrinsic skin features” include both (a) surface features of the skin, e.g., textural roughness, follicles, and wrinkles, and (b) sub-surface features, e.g., vascularity and pigmentation features. 
     In other embodiments, e.g., as discussed below with reference to  FIG. 45 , displacement sensor  200  may be a multiple-pixel sensor, such as a mouse-type optical sensor utilizing a two-dimensional array of pixels. 
     Depending on the particular embodiment, displacement sensor  200  (or a combination of multiple displacement sensors  200 ) may be used for (i) detecting, measuring, and/or calculating displacements of device  10  in one or more directions, or (ii) detecting, measuring, and/or calculating the degree of rotation travelled by device  10  in one or more rotational directions, or (iii) any combination thereof. 
     Displacement-based control system  132 , and in particular control electronics  30 , may control one or more controllable operational parameters of device  10  (e.g., operational aspects of treatment radiation source  14 , fans  34 , displays  32 , etc.) to achieve any of a variety of goals. For example, control electronics  30  may control treatment radiation source  14  and/or scanning system  48  (a) in order to avoid overtreatment of the same area of skin, (b) to provide desired spacing between adjacent or sequential treatment spots  70  or arrays of spots  70 , (c) to generate a relatively uniform pattern, or other desired pattern, of treatment spots  70 , (d) to restrict the delivery of radiation to particular tissue, such as human skin (i.e., to avoid delivering radiation to eye or to other non-skin surfaces), (e) and/or for any other suitable goals, and (f) and combination of the above. 
     In some embodiments, displacement-based control system  132  may be used in both a gliding mode and a stamping mode of device  10 . 
       FIG. 39  illustrates a flowchart of an example method  400  for controlling device  10  using displacement-based control system  132 , while device  10  is used either in a gliding mode or a stamping mode, according to certain embodiments. At step  402 , device  10  performs a first scan of input beam  110  to generate a first array (e.g., a row) of treatment spots onto the skin  40 . If device  10  is being used in a gliding mode, the user may glide device  10  across the skin while the first array of treatment spots is generated. If device  10  is being used in a stamping mode, the user may hold device  10  stationary on the skin while the first array of treatment spots is generated. Although the scan as step  402  is called the “first” scan in this description, it should be understood that method  400  is a continuously repeating or looping process during a treatment session, and thus the “first” scan may be any particular scan during the treatment session (e.g., the 37 th  scan during the process). 
     At step  404 , displacement-based control system  132  performs a first monitoring process to monitor and analyze the displacement of device  10  across the surface of the skin using displacement sensor  200 . For example, as discussed below, displacement-based control system  132  may analyze signal  360  to identify and count surface features  74  in the skin (e.g., in embodiments utilizing a single-pixel displacement sensor  200  (e.g., sensors  200 A,  200 B, or  200 C discussed below)), or compare images scanned at different times (in embodiments utilizing a multi-pixel displacement sensor  200  (e.g., sensor  200 D discussed below)), as device  10  is moved across the skin (e.g., in a gliding mode, during and/or after the generation of the first array of treatment spots; or in a stamping mode, after the generation of the first array of treatment spots). System  130  may begin the first monitoring process at the initiation of the first scan or upon any other predefined event or at any predetermined time. 
     At step  406 , displacement-based control system  132  controls a second scan of input beam  110  (for generating a second array of treatment spots onto the skin  40 ) based on the displacement of device  10  determined in the at step  404  (i.e., during the first monitoring process). For example, displacement-based control system  132  may initiate the second scan only after system  130  determines at step  404  that device  10  has moved more than a predetermined minimum distance across the skin (e.g., 1 mm). Thus, in such embodiments, a minimum spacing in the glide direction (e.g., 1 mm) between corresponding treatment spots  70  of adjacent rows  72  can be achieved regardless of the manual glide speed. 
     Single Pixel Displacement Sensor 
       FIG. 40A  illustrates an example single-pixel displacement sensor  200 A for use in displacement-based control system  132 , according to certain embodiments. Displacement sensor  200 A includes a light source  310 A, a light detector  312 A, a light guide  313  having an input and output portions  314  and  316 , a half-ball lens  318 , a ball lens  320 , a housing  322  for housing at least lenses  318  and  320  (and/or other components of sensor  200 A), and a and a microcontroller  330 . 
     Light source  310 A may be a light-emitting diode (LED) or any other suitable light source. Light source  310 A may be selected for detecting fine details in the surface or volume of human skin. Thus, a wavelength may be selected that penetrates a relatively shallow depth into the skin before being reflected. For example, light source  310 A may be a blue LED having a wavelength of about 560 nm, or a red LED having a wavelength of about 660 nm, or an infrared LED having a wavelength of about 940 nm. Red or infrared wavelength LEDs are relatively inexpensive and work well in practice. Alternatively, a semiconductor laser or other light source could be used. 
     Light detector  312 A may be a photodiode, phototransistor, or other light detector. In some embodiments, a phototransistor has sufficient current gain to provide a directly usable signal, without requiring additional amplification. 
     Light guide  313  is configured to guide light from light source  310 A (via input portion  314 ) and guide light reflected off the skin to detector  312 A (via output portion  316 ). Input portion  314  and output portion  316  may comprises optical fibers or any other suitable light guides. Light guide  313  may be omitted in some embodiments in which light source  310 A and detector  312 A are close enough to the skin surface to image or convey the light directly onto the skin surface, or alternatively using suitable optics to image or convey light source  310 A and detector  312 A directly onto the skin surface. 
     Microcontroller  330  may be configured to drive light source  310 A and receive and analyze signals from light detector  312 A. Microcontroller  330  may include an analog-to-digital converter (ADC)  332  for converting and processing analog signals from light detector  312 A. 
     In operation of this embodiment, light (for example, visible or near-IR energy) from light source  310 A travels down input light guide  314  and through half-ball lens  318  and ball lens  320 , which focuses the light on the skin surface  38 . Some of this light is reflected and/or remitted by the skin and returns through ball lens  320 , half-ball lens  318 , and output light guide  316 , toward light detector  312 A, which converts the light into an electrical signal, which is then delivered to microcontroller  330 . The light may be modulated to permit discrimination of a constant background ambient illumination level from the local light source. 
     Detector  312 A may deliver analog signals to microcontroller  330 , which may convert the signals to digital signals (using integrated ADC  332  or suitable alternatives), and perform computations regarding on the amplitude of the recorded signal over time to identify and count features in the skin and determine a relative displacement device  10  accordingly, as discussed below. 
     The amount of light that is returned to detector  312 A is a strong function of the distance “z” between the sensor optics and skin surface  38 . With no surface present only a very small signal is generated, which is caused by incidental scattered light from the optical surfaces. In addition to displacement sensor, this characteristic can be exploited to provide a contact sensor in another embodiment. When the skin surface  38  is within the focal distance of the lens  320 , a much larger signal is detected. The signal amplitude is a function of distance z as well as surface reflectivity/remittance. Thus, surface texture features on the skin surface create a corresponding signal variation at detector  312 A. Microcontroller  330  is programmed to analyze this signal and identify intrinsic skin features  74  that meet particular criteria. Microcontroller  330  may count identified features and determine an estimated displacement of sensor  200 A relative to the skin  40  in the x-direction (i.e., lateral displacement), based on knowledge of estimated or average distances between intrinsic skin features  74  for people in general or for a particular group or demographic of people, as discussed below. 
     Displacement sensor  200 A as described above may be referred to as a “single-pixel” displacement sensor  200 A because it employs only a single reflected/remitted beam of light for generating a single signal  360 , i.e., a single pixel. In other embodiments, displacement sensor  200  may be a multi-pixel sensor that employs two pixels (i.e., two reflected beams of light for generating two signals  360 ), three pixels, four pixels, or more. Multi-pixel displacement sensors  200  may be configured such that the multiple pixels are arranged along a single linear direction (e.g., along the glide direction, the scan direction, or any other direction), or in any suitable two-dimensional array (e.g., a circular, rectangular, hexagonal, or triangular pattern). 
       FIG. 40B  illustrates another example single-pixel displacement sensor  200 B for use in displacement-based control system  132 , according to certain embodiments. Displacement sensor  200 B includes a light source  310 B, a light detector  312 B, optics  342 , and a microcontroller  330 . 
     Light source  310 B and light detector  312 B may be provided in an integrated emitter-detector package  340 , e.g., an off-the-shelf sensor provided by Sharp Microelectronics, e.g., the Sharp GP2S60 Compact Reflective Photointerrupter. Light source  310 B may be similar to light source  310 A discussed above, e.g., a light-emitting diode (LED) or any other suitable light source. Light detector  312 B may be similar to light source  310 A discussed above, e.g., a photodiode, phototransistor, or other light detector. 
     Optics  342  may include one or more optical elements for directing light from light source  310 B onto the target surface and for directing light reflected/remitted from the target surface toward light detector  312 B. In some embodiments, optics  342  comprises a single lens element  342  including a source light focusing portion  344  and a reflected light focusing portion  346 . As shown, source light focusing portion  344  may direct and focus light from light source  310 B onto the skin surface  38 , and reflected light focusing portion  346  may direct and focus reflected light onto detector  312 B. Lens element  342  may have any suitable shape for directing and focusing the source light and reflected light as desired. 
     Microcontroller  330  may be configured to drive light source  310 B and receive and analyze signals from light detector  312 B. Microcontroller  330  may include an analog-to-digital converter (ADC)  332  for converting and processing analog signals from light detector  312 B. 
     The operation of sensor  200 B—including the operation of light detector  312 B and microcontroller  330 —may be similar to that described above with reference to sensor  200 A of  FIG. 40A . That is, detector  312 B may record a signal having an amplitude or other property that corresponds to a distance z perpendicular to the target surface or other properties indicative of intrinsic skin features. Detector  312 B may deliver analog signals to microcontroller  330 , which may convert the signals to digital signals (using integrated ADC  332 ), and perform computations regarding the recorded signal over time to identify and count features in the skin and determine a relative displacement of device  10  accordingly. 
     Like displacement sensor  200 A, displacement sensor  200 B may be referred to as a “single-pixel” displacement sensor  200 B because it employs only a single reflected beam of light for generating a single signal  360 , i.e., a single pixel. 
       FIG. 40C  illustrates yet another example single-pixel displacement sensor  200 C for use in displacement-based control system  132 , according to certain embodiments. Displacement sensor  200 C is generally similar to displacement sensor  200 B shown in  FIG. 40B , but omits the lens element  342  of displacement sensor  200 B. 
     Displacement sensor  200 C includes a light source  310 C, a light detector  312 C, optics  342 , and a microcontroller  330 . Light source  310 C and light detector  312 C may be provided in an integrated emitter-detector package  340 , e.g., an off-the-shelf sensor provided by Sharp Microelectronics, e.g., the Sharp GP2S60 Compact Reflective Photointerrupter. Light source  310 C may be similar to light source  310 A/ 310 B discussed above, e.g., a light-emitting diode (LED) or any other suitable light source. Microcontroller  330  may be configured to drive light source  310 C with a direct or modulated current. Light detector  312 C may be similar to light source  310 A discussed above, e.g., a photodiode, phototransistor, or other light detector. 
     The integrated (or non-integrated) emitter-detector package  340  may be housed in an opaque enclosure  390 , having a clear aperture  392  in the front which is covered by a window  394  (for example a transparent plastic, or glass). Infrared light from light source  310 C (e.g., LED) shines through the aperture  392  and impinges on the skin surface  38 . Some of this light (reflected/remitted from the skin  40 , as well as scattered from the interior volume of opaque enclosure  390 , returns through aperture  392  and reaches detector  312 C (e.g., photodetector), which converts the received light into an electrical signal. The light may be modulated to permit discrimination of a constant background ambient illumination level from the local light source. 
     The amount of light that is returned to detector  312 C is a strong function of the distance “z” between the skin surface  38  and the optical aperture  392 . When the skin surface  38  is close to or in contact with window  394 , a larger signal is detected. With no surface presented to the detector, a smaller optical signal remains, due to reflections from the surface of opaque mask  390  and window  394 , as well as background light from exterior illumination sources. 
     Thus, the signal amplitude recorded by detector  312 C is a function of z-height as well as skin reflectivity/remittance. Surface texture features  74  create a corresponding signal variation at detector  312 C. Detector  312 C may deliver the recorded analog signals (with the amplitude being at least indicative of z-height) to microcontroller  330 , which may convert the signals to digital signals (using integrated ADC  332 ), and perform computations regarding the recorded signal over time to identify features  74  in the skin (based on the signal amplitude), count or otherwise process such identified features  74 , and determine a relative displacement of device  10  accordingly. 
     Integrated emitter-detector pairs used for the proximity detector may be compact, inexpensive, and readily available. It is also possible to use a separate emitter and detector. Any suitable wavelength range of light may be used, but infrared may be selected due to the sensitivity of the detector  312 C (e.g., phototransistor), and ability to block out visible light with an IR-pass filter over the detector. Also, different skin types show more uniform reflectance levels in IR than in shorter wavelengths. Test results show that a phototransistor has sufficient current gain to provide a directly usable signal to the integrated ADC  332  of microcontroller  330 , without requiring additional amplification. 
     Like displacement sensors  200 A and  200 B, displacement sensor  200 C may be referred to as a “single-pixel” displacement sensor  200 C because it employs only a single reflected beam of light for generating a single signal, i.e., a single pixel. 
       FIG. 41  illustrates a pair of experimental data plots for an embodiment of optical displacement sensor  200 C being scanned above the skin surface  38  of a human hand. The photodetector signal (y-axis) is shown versus time (x-axis) in arbitrary units. The area without dense peaks indicates times in which the sensor aperture  392  is held against a fixed area of the skin. An algorithm takes as input the photodetector signal to generate the lower “detected output” plot, which is a signal suitable for controlling device  10 . For example, microcontroller  330  may be programmed to analyze the photodetector signal and identify intrinsic skin features  74  that meet particular criteria, e.g., using any of the various techniques or algorithms disclosed herein, or any other suitable techniques or algorithms. In some embodiments, microcontroller  330  may count identified features and determine an estimated displacement of sensor  200 C relative to the skin  40  in the x-direction (i.e., lateral displacement), based on knowledge of estimated or average distances between intrinsic skin features  74  for people in general or for a particular group or demographic of people, as discussed below. 
     Certain embodiments of single-pixel displacement sensor  200 , e.g., sensors  200 A,  200 B, and/or  200 C discussed above, may not require imaging optics, as compared to imaging-type sensors. Further, certain embodiments of single-pixel displacement sensor  200  may not require close proximity between the electronics (e.g., microcontroller) and the target surface to be sensed. For example, the light source and/or detector may be spaced away from the target surface, with light guides or relay optics used to convey light between the light source/detector and the target surface. As another example, the light source and/or detector may be spaced relative close to the target surface, but may be coupled to a relatively remote microcontroller by wiring. 
     Further, in certain embodiments of single-pixel displacement sensor  200 , e.g., sensors  200 A,  200 B, and  200 C discussed above, the active components (e.g., light source, detector, etc.) and the active sensing area are relatively small (e.g., as compared to a standard optical mouse-type imaging sensor). Thus, in embodiments in which single-pixel displacement sensor  200  is located at the application end  42  of device  10 , sensor  200  may occupy relatively little real estate on the application end  42  (e.g., as compared to a standard optical mouse-type imaging sensor), which may allow the total size of application end  42  to be reduced in at least one dimension, which may be advantageous in certain embodiments. 
       FIG. 42  represents an example plot  350  of a signal  360  generated by detector  312 A,  312 B, or  312 C as sensor  200 A,  200 B, or  200 C is moved across the skin of a human hand in the x-direction. The x-axis of plot  350  may be scaled such that the movement of the signal  360  on the x-axis matches the distance of movement of sensor  200 A/ 200 B/ 200 C across the skin. 
     The amplitude of the signal  360  corresponds with the texture of the skin surface, which includes numerous intrinsic skin features  74 . As shown, signal  360  includes a series of peaks  362 , valleys  364 , and other characteristics. Intrinsic skin features  74  may be identified from signal  360  based on any suitable parameters or algorithms. 
     For example, one or more of the following criteria may be used for identifying intrinsic skin features  74  based on signal  360 :
         (a) the raw amplitude of a peak  362 ,   (b) the amplitude of a peak  362  relative to the amplitude of one or more other peaks  362  (e.g., one or more adjacent peaks  362 ),   (c) the amplitude of a peak  362  relative to the amplitude of one or more valleys  364  (e.g., one or more adjacent valleys  364 ),   (d) the raw amplitude of a valley  364 ,   (e) the amplitude of a valley  364  relative to the amplitude of one or more other valleys  364  (e.g., one or more adjacent valleys  364 ),   (f) the amplitude of a valley  364  relative to the amplitude of one or more valleys  364  (e.g., one or more adjacent valleys  364 ),   (g) the rate of increase in amplitude of signal  362  (i.e., positive slope of signal  360 ) for a particular portion of signal  360 ,   (h) the rate of decrease in amplitude of signal  360  (i.e., negative slope of signal  360 ) for a particular portion of signal  362 ,   (i) the x-direction distance between adjacent peaks  362  (D 1 , D 2 , D 3 , etc),   (j) the x-direction distance between adjacent valleys  364 , or   (k) any other suitable criteria.       

     An algorithm  154  may identify intrinsic skin features  74  based on any one or any combination of more than one of the criteria listed above. Such algorithm  154  may include (predefined or real-time calculated) threshold values to which one or more of the criteria listed above are compared. In some embodiments that identify intrinsic skin features  74  based on peaks  362  in signal  360 , the algorithm  154  may be able to distinguish major or global peaks (e.g., peaks  362 ) from minor or local peaks (e.g., local peak  368 ), and use only the major or global peaks  362  for identifying intrinsic skin features  74 . As another example, the algorithm  154  may distinguish major or global valleys (e.g., valleys  364 ) from minor or local valleys (e.g., local valley  369 ), and use only the major or global valleys  364  for identifying intrinsic skin features  74 . 
     One example displacement algorithm that may be used with a single-pixel displacement sensor (e.g., sensor  200 A,  200 B, or  200 C) to identify intrinsic skin features  74 , and detect displacement of device  10 , is discussed below with reference to  FIG. 43 .  FIG. 43  illustrates three data plots: a raw signal plot  370 , filtered signal plot  372 , and an intrinsic skin feature detection plot  374 . The example displacement algorithm takes as input a raw signal from a photodetector (representing reflectance/remittance vs. time), and generates as output a digital pulse “1” when a displacement has been detected, and “0” when no displacement has been detected. In  FIG. 43 , each plot  370 ,  372 , and  374  shows the specified signals plotted against time on the horizontal axis. 
     Raw signal plot  370  shows the raw input signal “pd 1 ”  376 , which includes amplitude variations corresponding to displacement of the sensor across the skin (the amplitude variations correspond to intrinsic skin features  74  on the skin), and flatter areas corresponding to the sensor dwelling in the same place on the skin. 
     As shown in filtered signal plot  372 , the algorithm extracts a high-pass filtered version “diff 1 ”  378  of the raw signal pd 1  and also a positive-tracking and negative-tracking envelope indicated as “max 1 ”  380  and “min 1 ”  382 , respectively. The positive envelope “max 1 ”  380  is created at each point in time by adding a fraction of the current high-pass-filtered positive signal “dif 1   p ” to the previous time-step value of the positive envelope signal “max 1 ”, where “dif 1   p ” is formed from the high-pass filtered signal “dif 1 ”:
 
dif1 p =dif1 (dif1&gt;0)
 
dif1 p= 0 (dif1&lt;=0)
 
     Similarly, the negative envelope “min 1 ”  382  is created the same way from “dif 1   n ”, which is the high-pass filtered negative signal:
 
dif1 n =dif1 (dif1&lt;0)
 
dif1 n= 0 (dif1&gt;=0)
 
     Finally, as shown in the intrinsic skin feature detection plot  374 , the feature-detect signal “d 1 ”  384  is set to 1 at any time step in which “dif 1 ” has a zero crossing (i.e., where previous time step and current time step have a different sign) AND “max 1 ” exceeds a threshold value, AND “min 1 ” exceeds a threshold value. Otherwise, “d 1 ” is set to 0. The threshold limits may be designed to prevent non-desirable outputs (e.g., feature-detection false positives and/or false negatives) due to random sensor or circuit noise levels. The zero-crossing requirement may also be designed to prevent non-desirable outputs (e.g., feature-detection false positives and/or false negatives) when the photosignal dif 1  is entirely positive or negative, as when the photosensor is initially brought up against a surface (signal shows large increase with time), or removed from it (signal decreases). 
     From feature detection plot  374 , the displacement of the sensor relative to the skin can be determined by counting the number of detected features  74 . The algorithm may then make control decisions by (a) comparing the number of detected features  74  to one or more predetermined threshold numbers (e.g., allow continued treatment if at least three features  74  have been detected), or (b) by multiplying the number of detected features  74  by a known nominal or average distance between features  74  (e.g., as determined based on experimental testing) to determine displacement distance (e.g., in millimeters), and then comparing the determined displacement distance to one or more predetermined threshold distances (e.g., allow continued treatment if the determined displacement exceeds 2 mm). It can be appreciated by one of ordinary skill in the art that, if desired, this embodiment could also be used to create a velocity sensor if rate information was also obtained and used or a dwell sensor. 
     In some embodiments, the example algorithm may be utilized in a system including a single sensor (e.g., single-pixel displacement sensor  200 A,  200 B, or  200 C) having a single detector (e.g., detector  312 A or  312 B). In other embodiments, the example algorithm may be utilized in a system with more than one sensors (e.g., more than one sensor  200 A,  200 B, and/or  200 C) or with a sensor  200  that includes more than one detector  312  (e.g., a sensor  200 A,  200 B, or  200 C including more than one detector  312 A,  312 B, or  312 C). Such embodiments may thus generate multiple feature detection signals  384 , each corresponding to a different sensor  200  or detector  312  with the same type of features detected or different types of features detected. 
     In embodiments including multiple sensors  200  or detectors  312 , the algorithm may make control decisions based on the multiple feature detection signals  384  in any suitable manner. For example, the algorithm may generate a control signal only if each of the multiple feature detection signals  384  detects a predetermined number of features  74  (which may provide relatively greater resistance to noise or possible fault conditions). Or, the algorithm may generate a control signal if any of the multiple feature detection signals  384  detects a predetermined number of features  74  (which may provide relatively greater detection sensitive for surfaces with less texture and smaller amplitude reflectance features). Or, the algorithm may generate control signals based on the total number of features  74  detected by the multiple feature detection signals  384 . The algorithm can also be designed to the identify an outlier feature detection signal  384  (as compared to the other feature detection signal  384 ), and ignore such signal  384 , at least while it remains an outlier. 
     A sample of humans was tested with a particular embodiment of sensor  200 A, and identifying intrinsic skin features  74  according to the example algorithms discussed above. The testing involved moving sensor  200 A in a straight line across the surface of the test subjects&#39; skin, such as face or arm skin. The resulting test data using the particular embodiment of sensor  200 A indicated that adjacent intrinsic skin features  74  (texture or roughness, in this case) are located about 0.3-0.4 mm apart on average. In other words, with reference to  FIG. 42 , the test data indicated an average spacing D 1 , D 2 , D 3 , etc. of about 0.3-0.4 mm. 
     The displacement of device  10  can be determined or approximated using this experimental data, e.g., the average spacing between intrinsic skin features  74 . For example, the displacement of device  10  can be determined or approximated by multiplying the number of intrinsic skin features  74  identified by system  132  by the experimentally determined average spacing between intrinsic skin features  74 . 
     Thus, displacement-based control system  132  (e.g. by cooperation with radiation source control system  128  and/or scanning system control system  130 ) may control device  10  based on the determined or approximated displacement of device  10  across the skin. For example, displacement-based control system  132  may control one or more controllable operational parameters of device  10  (e.g., operational aspects of treatment radiation source  14  and/or scanning system  48 ) based on the number of surface features  74  identified by system  132  for a displacement of device  10  across the skin. For example, system  132  may control device  10  to deliver one scanned array of beams  114  each time device  10  is displaced X mm, as determined by identifying N surface features  74 . For example, if experimental data indicates that surface features  74  are spaced by an average of 0.4 mm, system  132  may control device  10  to deliver one scanned array of treatment spots each time device  10  is displaced approximately 1.2 mm, as determined by identifying three surface features  74 ; the next scanned array of beams  114  is not delivered until/unless device  10  is displaced another approximately 1.2 mm (i.e., until three surface features  74  are identified by system  132 ). Additional details and examples of the control of device  10  by system  132  are provided below. 
     Thus, in some embodiments, control systems  18 , including displacement-based control system  132 , controls operational aspects of device  10  (e.g., operational aspects of treatment radiation source  14 ) based on the displacement of device  10  across the skin, independent of the rate, speed, or velocity of device  10  moving across the skin. In some embodiments device  10 , including displacement-based control system  132 , is not configured for detecting or measuring any data indicative of the rate, speed, or velocity of device  10  moving across the skin, or for determining or attempting to determine the rate, speed, or velocity of device  10  moving across the skin. Rather, device  10  is configured for detecting or measuring data indicative of the lateral displacement of device  10  relative to the skin, and for determining the lateral displacement of device  10  using such data, e.g., as discussed above. In other words, device  10  can be moved at any rate, including very slowly, and beams  114  are delivered only if sufficient distance has been translated relative to the delivery of a particular prior beam  114  or some other predetermined event. 
     In other embodiments, device  10  may include a speed detection system, e.g., including a motion/speed sensor  202 , for detecting or measuring data indicative of the rate, speed, or velocity of device  10  moving across the skin, and for determining or attempting to determine the rate, speed, or velocity of device  10  based on such data. Such speed detection sensor or system may be provided in addition to, or in place of, displacement-based control system  132  and displacement sensor  200 . 
     In other embodiments, device  10  may include a dwell sensor  216  for measuring data indicative of whether device  10  is stationary or stationary within a certain tolerance with respect to the skin. Dwell sensor  216  may employ aspects of displacement sensor  200  described above but may be configured to provide information specifically about whether device  10  is stationary. For example, all or portions of the example algorithm described above for single-pixel displacement sensor  200 A/ 200 B may be used to determine when device  10  is substantially stationary (e.g., by recognizing the flat spots in the raw data signal  376  shown in  FIG. 43 ) and device  10  may be controlled based on that information (e.g., radiation source  14  may be disabled if device  10  is determined to be stationary or dwelling). 
       FIG. 44  illustrates a more specific example of the general method  400  of  FIG. 39 . In particular,  FIG. 44  illustrates a method  420  for controlling device  10  using displacement-based control system  132  that employs a single-pixel displacement sensor  200 A, while device  10  is used either in a gliding mode or a stamping mode, according to certain embodiments 
     At step  422 , device  10  initiates and performs a first scan of input beam  110  to generate a first array (e.g., a row  72 ) of treatment spots  70  onto the skin  40 , as discussed above regarding step  402 . As discussed above regarding method  400  of  FIG. 39 , although the scan in step  422  is called the “first” scan in this description, it should be understood that method  420  is a continuously repeating or looping process during a treatment session, and thus the “first” scan may be any particular scan during the treatment session (e.g., the 124 th  scan during the process). 
     At step  424 , displacement-based control system  132  initiates a monitoring process upon the initiation of the first scan, to monitor and analyze the lateral displacement of device  10  across the surface of the skin using sensor  200 A. Displacement-based control system  132  analyzes signal  360  to identify and maintain a count of surface features  74  in the skin as device  10  is moved across the skin (e.g., in a gliding mode, during and/or after the generation of the first array (e.g., row  72 ) of treatment spots  70 ; or in a stamping mode, after the generation of the first array of treatment spots  70 ). 
     At step  426 , system  132  determines whether a predetermined minimum number of surface features  74  (corresponding to a minimum lateral displacement of device  10 ) have been identified by the completion of the first scan of input beam  110 . If so, the method returns to step  422  where the next (second) scan begins continuously upon completion of the first scan, and the process continues. If not, system  132  delays the initiation of the second scan and continues the first monitoring process (i.e., the method returns to step  424 ) until system  132  identifies the predetermined minimum number of surface features  74  (i.e., until system  132  determines that device  10  has traveled the minimum lateral displacement). Once system  132  has identified the predetermined minimum number of surface features  74 , in some embodiments device  10  initiates the second scan of input beam  108  immediately, regardless of the rotational position of rotating scanning element  100  (i.e., the second scan may begin at any sector  104  of element  100 ). In other embodiments, device  10  waits until rotating scanning element  100  is positioned in a particular position to initiate the second scan immediately (e.g., such that the second scan begins at a predetermined “first” sector  104 ). 
     In this manner, system  132  ensures that each successively delivered array (e.g., row  72 ) of spots  70  is spaced apart from the previously generated array (e.g., row  72 ) in the glide direction by at least the predetermined distance corresponding to the predetermined minimum number of surface features  74  identified in the skin. As mentioned above, this method can be applied in both a gliding mode and a stamping mode of device  10 . 
     In this example method, device  10  (e.g., operational aspects of treatment radiation source  14  and/or scanning system  48 ) is controlled based on the displacement of device  10  across the skin, regardless of the rate, speed, or velocity of device  10  moving across the skin. As discussed above, in some embodiments device  10  is not configured for detecting or measuring any data indicative of the rate, speed, or velocity of device  10  moving across the skin, or for determining or attempting to determine the rate, speed, or velocity of device  10  moving across the skin. 
     Multi-Pixel Displacement Sensor 
     As mentioned above, in some embodiments displacement sensor  200  is a multi-pixel displacement sensor  200  that employs two pixels (i.e., two reflected beams of light for generating two signals  360 ), three pixels, four pixels, or more. For example, some embodiments employ a multi-pixel imaging correlation sensor  200 D, of the type used in optical mice for computer input, for detecting displacement along the skin. 
       FIG. 45  illustrates an example multi-pixel imaging correlation sensor  200 D, of the type used in certain types of optical mouse for computer input, for detecting displacement along the skin, according to certain embodiments. Displacement sensor  200 D may include a radiation source  310 D, a light detector  312 D, and a processor  334 . 
     Radiation source  310 D may be a light-emitting diode (LED) or any other suitable radiation source, e.g., as discussed above regarding radiation source  310 A. Radiation source  310 D may be arranged to deliver light at an oblique angle with respect to the skin surface  38 , as shown in  FIG. 45 . 
     Light detector  312 D may include a molded lens optic  336  and an imaging chip  338 . In some embodiments, sensor  200 C is configured such that the skin is within the focal plane of molded lens optic  336 , which focal plane may be located several millimeters away from the surface of molded lens optic  336 , as indicated by distance z in  FIG. 45 . Optionally, a system of relay lenses may be added between detector  312 D and skin surface  38  to extend the total distance from the external focal plane to detector  312 D. 
     Detector  312 D may be configured to generate a two-dimensional multi-pixel “image” of the area of skin surface  38  illuminated by radiation source  310 D. The image may consists of a two-dimensional array of pixels, each pixel having a signal  360  similar to signal  360  of single-pixel sensor  200 A,  200 B, OR  200   c . Imaging chip  338  may be configured to generate a digital output stream to processor  334  corresponding to the multi-pixel signal array. 
     Processor  334  may be configured to drive radiation source  310 D and receive and analyze the multi-pixel array of signals from light detector  312 D. In particular, processor  334  may compare different multi-pixel images received from detector  312 D (e.g., successively received images) to determine linear displacements in one or more directions, rotational displacements, and/or lateral displacements of sensor  200 D across the skin surface  38 . 
       FIG. 46  illustrates an example method  440  for controlling device  10  using displacement-based control system  132  that employs a multi-pixel displacement sensor  200 C, while device  10  is used either in a gliding mode or a stamping mode, according to certain embodiments. 
     At step  442 , device  10  initiates and performs a first scan of input beam  110  to generate a first array (e.g., a row  72 ) of treatment spots onto the skin  40 , as discussed above regarding step  402 . Again, as discussed above regarding methods  400  and  420 , although the scan in step  442  is called the “first” scan in this description, it should be understood that method  440  is a continuously repeating or looping process during a treatment session, and thus the “first” scan may be any particular scan during the treatment session. 
     At step  444 , displacement-based control system  132  initiates a monitoring process upon the initiation of the first scan of input beam  110 , to monitor and analyze the lateral displacement of device  10  across the surface of the skin using sensor  200 C. Displacement-based control system  132  analyzes signals  360  as device  10  is moved across the skin (e.g., in a gliding mode, during and/or after the generation of the first array of treatment spots; or in a stamping mode, after the generation of the first array of treatment spots). 
     At step  446 , system  132  determines whether device  10  has been displaced a predetermined minimum distance along the skin by the completion of the first scan of input beam  110 . If so, the method returns to step  442  where the next (second) scan begins continuously upon completion of the first scan, and the process continues. If not, system  132  delays the initiation of the second scan and continues the first monitoring process (i.e., the method returns to step  444 ) until system  132  determines that device  10  has travelled the predetermined minimum distance across the skin. Once system  132  determines that device  10  has travelled the predetermined minimum distance, in some embodiments device  10  initiates the second scan of input beam  110  immediately, regardless of the rotational position of rotating scanning element  100  (i.e., the second scan may begin at any sector  104  of element  100 ). In other embodiments, device  10  waits until rotating scanning element  100  is positioned in a particular position to initiate the second scan immediately (e.g., such that the second scan begins at a predetermined “first” sector  104 ). 
     In this manner, system  132  ensures that each successively delivered array (e.g., row  72 ) of spots  70  is spaced apart from the previously generated array (e.g., row  72 ) in the glide direction by at least the predetermined distance corresponding to the predetermined minimum number of surface features  74  identified in the skin. As mentioned above, this method can be applied in both a gliding mode and a stamping mode of device  10 . 
     In this example method, device  10  (e.g., operational aspects of treatment radiation source  14  and/or scanning system  48 ) is controlled based on the displacement of device  10  across the skin, regardless of the rate, speed, or velocity of device  10  moving across the skin. As discussed above, in some embodiments device  10  is not configured for detecting or measuring any data indicative of the rate, speed, or velocity of device  10  moving across the skin, or for determining or attempting to determine the rate, speed, or velocity of device  10  moving across the skin. 
     Treatment Sessions 
     In some embodiments, control system  18  defines and controls individual treatment sessions based on one or more “treatment delimiters” such as (a) a total number of treatment spots/MTZs generated in the skin  40 , (b) a total number of scans of beam  110 , (c) a total amount of energy delivered to the skin  40 , (d) a total treatment time, or any other suitable delimiter(s). 
     In some embodiments, treatment delimiters are specified for different “types” of treatments. Different types of treatments may include (a) treatments for different areas of the body (e.g., periorbital area, areas near the mouth, the back of the hand, the stomach, the knees, etc.), (b) different treatment energy or intensity levels (e.g., high energy treatment, medium energy treatment, low energy treatment), (c) different treatments for different stages of a multi-session treatment plan (e.g., a first session treatment, a mid-stage session treatment, or a final-session treatment), or any other different types of treatments. 
     Further, treatment delimiters may be specified for different combinations of treatment types. For example, different values for a total treatment spot/MTZ delimiter may be specified for different combinations of treatment area and treatment energy level. For example, device  10  may enforce the following delimiter value: (a) for a full-face treatment (e.g., based on an assumed area of 300 cm2), 39,000 MTZs for a high energy full-face treatment; 21,600 MTZs for a medium energy full-face treatment; and 10,800 MTZs for a low energy full-face treatment; (a) for a periorbital area treatment (e.g., based on an assumed area of 20 cm2), 2,600 MTZs for a high energy periorbital treatment; 1,440 MTZs for a medium energy periorbital treatment; and 720 MTZs for a low energy periorbital treatment; and (c) for treatment of both hands (e.g., based on an assumed area of 150 cm2), 19,500 MTZs for a high energy hand treatment; 10,800 MTZs for a medium energy hand treatment; and 5,400 MTZs for a low energy hand treatment; and (c) 
     Treatment delimiters for different treatment types (or combinations of different treatment types) may be predetermined and programmed into device  10 , set or modified by a user via a user interface  18 , determined by device  10  based on user input, settings stored in device  10 , and/or algorithms  148  stored in device  10 , or determined in any other suitable manner. In some embodiments, treatment delimiters for different treatment types are determined based on experimental testing and preprogrammed into device  10 . For example, experimental testing may determine that an appropriate treatment session for the full face involves 10,000-45,000 treatment spots, an appropriate treatment session for a periorbital region involves 700-3,000 treatment spots, an appropriate treatment session for a mouth region involves 2,700-11,000 treatment spots, and an appropriate treatment session for the back of the hand involves 5,400-22,000 treatment spots. These treatment delimiters may be stored in device  10  and implemented by control system  18  as appropriate when a user selects from a “full face treatment,” “periorbital treatment,” “mouth treatment,” or “hand treatment” via user interface  18 . 
     Where treatment sessions are defined by treatment delimiters that are not time-based, such as treatment sessions defined by (a) a total number of treatment spots, (b) a total number of beam scans, or (c) a total amount of energy delivered to the target, the rate or speed at which the user moves device  10  across the skin (e.g., glide speed)—with the possible exception of extremely fast gliding velocities—may be largely or substantially irrelevant to the effectiveness of the treatment delivered during the session, at least in certain embodiments or configurations of device  10 . For example, the glide speed may influence the number of times device  10  must be glided across the skin  40  to complete the treatment session (e.g., the faster the glide speed, the more glides are required to complete the session), but does not affect the specified treatment delimiter for the session, e.g., the total number of treatment spots or the total amount of energy delivered to the skin  40 . 
     Further, in some embodiments, the effectiveness of the treatment, as related to the spacing between treatment spots, is generally not affected by the glide speed of device  10 . In embodiments that include displacement-based control system  132 , which controls beam delivery, and thus treatment spot generation, based on the determined displacement of device  10  across the skin, system  132  ensures at least a minimum spacing between successive scanned treatment spot rows/arrays, which reduces or substantially eliminates the chances of over-irradiation of any area. In particular, displacement-based control system  132  may ensure at least a minimum spacing between successive scanned treatment spot rows/arrays during slow glide velocities, and without detecting or determining the glide speed. Thus, displacement-based control system  132  may reduce or substantially eliminate the chances of over-irradiation of any particular area, even for very slow glide velocities. 
     Further, where the treatment session involves multiple glides of device  10  across the skin  40 , the treatment spots generated during different glides typically will not align with other, which generally results in an treatment spot pattern with sufficient or desirable randomness and/or density uniformity to provide the desired treatment effects, without over-irradiating any areas. Thus, although rapid glide velocities may require the user to perform more glides to reach the relevant treatment delimiter (e.g., total treatment spots generated or total energy delivered), rapid glide velocities may provide a sufficient or desirable treatment spot patterns, without over-irradiating any areas. 
     It should be noted that the glide speed may influence the shape of individual treatment spots, e.g., the extent of elongation, “blurring,” or “smearing” of treatment spots, such as described above with respect to  FIG. 26B . Thus, operational aspects of device  10  may be configured such that within a reasonable range of glide velocities (i.e., less than very fast glide velocities), the elongation or smearing of treatment spots does not substantially affect the physiological effectiveness of the treatment spots. In some embodiments or configurations of device  10 , at very high glide velocities, the elongation or smearing of treatment spots may significantly reduce the effectiveness of the treatment. For example, the energy density within a very elongated treatment spot may be too low to provide the intended effects. Thus, the user may be provided general guidance (e.g., via display  32  or in a user manual) regarding the rate or speed at which to move device  10  to ensure the desired treatment effects. For example, the user may be instructed to glide device  10  across the skin  40  at a rate or speed of roughly three seconds per glide. 
       FIG. 47  illustrates an example method  460  for executing a treatment session for providing treatment (e.g., fractional treatment) to a user with device  10 . At step  462 , one or more delimiters for a treatment session to be performed are determined in any suitable manner, e.g., as discussed above. For the purposes of this discussion it is assumed that a single treatment delimiter is determined. For example, control system  18  may determine a predefined total number of treatment spots for the treatment session based on a treatment area (e.g., full face or periorbital area) selected by the user via a user interface  18 : for example, 1200 treatment spots. (The number of treatment spots may be assumed to be equal to the number of output beams  112  output by device  10 ). 
     At step  464 , after the user has positioned device  10  against the skin  40 , device  10  may begin the treatment session. In particular, control system  18  may deliver scanned arrays (e.g., rows  72 ) of beams  114  to the skin  40 , thus generating an array of treatment spots  70 , as indicated at step  466 . If device is operating in a gliding mode, device  10  may glided across the skin continuously during the beam-scanning and delivery process. If device is operating in a stamping mode, device  10  may held in place during each scan, and then moved, or glided, across the surface of skin to the next treatment location for performing the next scan. The user may be instructed (e.g., by audible, visible, or tactile notifications) when each scan of input beam  110  begins and ends, and/or whether or when device  10  has been moved a sufficient distance for performing the next scan (as determined by displacement monitoring and control system  132 ). In either the gliding mode or the stamping mode, the user may glide or move the device across the skin  40  any number of times (e.g., to “paint” a desired area of skin) during the treatment session. 
     During the treatment session, as indicated as step  468 , displacement monitoring and control system  132  may monitor the lateral displacement of device as it moves across the skin and control the delivery of output beams/generation of treatment spots accordingly, as discussed above. For example, system  132  may ensure that consecutive rows of treatment spots are spaced apart in the glide direction by at least a minimum distance. 
     Also during the treatment session, control system  18  may monitor the treatment delimiter determined at step  462 , as indicated at step  470 . For example, control system  18  may maintain a running count of the number of treatment spots generated during the treatment session. Steps  468  and  470  may be performed concurrently throughout the duration of the treatment session. 
     At step  472 , control system  18  determines whether the treatment delimiter has reached the predetermined limit. For example, control system  18  may determine whether the number of treatment spots that have been generated during the session has reached the predefined number of treatment spots determined at step  462  (e.g., 1200 treatment spots). If so, the treatment session is completed at step  474 . For example, control system  18  may turn off treatment radiation source  14  and/or scanning system  48 . If not, steps  466 - 472  are continued until the treatment delimiter is reached. 
     In some embodiments, a treatment session for providing treatment (e.g., fractional treatment) to a user may be completed according to method  460  without regard to the rate or speed at which device  10  is moved across the skin, e.g., as discussed above. 
     Roller-Type Displacement Sensor or Motion/Speed Sensor 
     In some embodiments, device  10  may include one or more roller-based sensors  218  that function as a displacement sensor  200 , or dwell sensor  216  or as a motion/speed sensor  202 , or all. Roller-based sensor  218  may be arranged at or near the treatment tip  42  of device  10 , and may include a roller  480  having a leading surface that is generally flush with, or projects slightly forward from the leading surface of the surrounding or adjacent portion of housing  24 . In some embodiments, the leading surface of roller  480  may define a skin-contacting surface  74 , which may or may not affect the distance (if any) of the treatment window  44  from the skin surface, e.g., depending on the closeness of the roller  405  to the window  44  and/or the force at which device  10  is pressed against the skin by the user. 
       FIGS. 48A-48G  illustrate some example embodiments of a roller-based sensor  218 A- 118 G that may be used in certain embodiments of device  10 . Each embodiment includes a roller  480  coupled (e.g., mechanically, optically, magnetically, electrically, etc.) to a detection system  482  configured to generate signals indicative of (a) the displacement of device  10  (e.g., based on a detected amount of angular rotation of roller  45 ), or (b) the manual glide speed of device  10  (e.g., based on a detected speed of rotation of roller  45 ), or (c) a dwell sensor (e.g., based on rotation or not rotation), or (d) all of the above. 
     As device  10  is manually moved across the skin, roller  480  turns or “rolls” by a degree and at a speed corresponding to the lateral displacement and manual glide speed, respectively, of the device relative to the skin surface. Detection system  482 , via its coupling or interaction with roller  480 , generates signals indicative of the lateral displacement and/or manual glide speed, and communicates such signals to processor  150 , which may convert and/or process such signals to determine the displacement and/or glide speed and/or stationary status of device  10 . The determined displacement and/or glide speed and/or stationary status of device  10  may then be used for controlling one or more controllable operational parameters of device  10  (e.g., control operational parameters of radiation source  14 ), e.g., as discussed herein. 
     In some embodiments, roller-based sensor  218  is configured to operate as a displacement sensor  200  for use in displacement-based control system  132 , and may be used for any of the displacement-based control techniques discussed herein. In some embodiments, roller-based sensor  218  measures, detects, or generates signals indicative of, the displacement of device  10 , but does not measure, detect, or generate signals indicative of, the manual glide speed of device  10 . 
     In an example embodiment, roller  480  has a diameter of about 4 mm, such that a 29 degree rotation of roller  480  corresponds to 1 mm displacements of device  10  (assuming no slipping between roller  480  and skin). In some embodiments, detection system  482  may be sensitive to device displacements to a granularity of about 1 mm. 
       FIG. 48A  illustrates an example roller-based sensor  218 A that includes a belt-driven optical-interrupt detection system  482 A to generate signals indicative of the displacement and/or glide speed of device  10 . 
       FIGS. 48B and 48C  illustrate an example roller-based sensor  218 B that includes a detection system  482 B that generates signals indicative of the displacement and/or glide speed of device  10  based on the flexure of a physical arm, which causes strain across a Wheatstone bridge, thus causing changes in resistance corresponding to device movement. 
       FIG. 48D  illustrates an example roller-based sensor  218 D that includes a detection system  482 D that generates signals indicative of the displacement and/or glide speed of device  10  based on an interaction between a Hall-effect sensor and one or more magnets around the perimeter of roller  480 . 
       FIG. 48E  illustrates an example roller-based sensor  218 E that includes a detection  482 E to generate signals indicative of the displacement and/or glide speed of device  10  based on a measured capacitance between an “antenna” and a gear or other rotating element. 
       FIG. 48F  illustrates an example roller-based sensor  218 F that includes a detection system  482 F to generate signals indicative of the displacement and/or glide speed of device  10  based on measurements of reflected optical radiation. 
     Finally,  FIG. 48G  illustrates an example roller-based sensor  218 G that includes a gear-driven optical-interrupt detection system  482 G to generate signals indicative of the displacement and/or glide speed of device  10 . 
     Capacitive Sensors 
     One or more sensors  26  of device  10  may be, or may include, capacitive sensors. As discussed above, skin-contact sensor  204  may be a capacitive sensor, in which the signal amplitude is analyzed to determine whether sensor  204  is in contact or sufficient proximity with the skin. In addition, any of displacement sensor  200 , motion/speed sensor  202 , and/or dwell sensor  216  may be capacitive sensors, or may include capacitive sensors in addition to other types of sensors (e.g., a sensor  200 ,  202 , or  216  may include an optical reflectance/remittance sensor in addition to a capacitive sensor for providing the desired functionality, e.g., to provide redundancy). 
     A capacitive sensor in contact with the skin (e.g., a capacitive sensor located at the application end  42  of device  10  may generate a signal (e.g., a high-frequency signal) indicating a measure of capacitance associated with the contact between the sensor and the skin. For example, a capacitive sensor&#39;s signal may be inversely proportional to the relative displacement between the sensor and the target surface. Because the surface of a human&#39;s skin is not perfectly smooth and/or because a human cannot achieve perfectly steady motion during manual movement of device  10 , static friction (stiction) between device  10  and the skin and/or other physical principles may result in “stick-and-slip” movement of device  10  across the skin, which causes micro-displacement between the sensor and the skin surface. This micro-displacement due to stick-and-slip movement of device  10  may result in a translational signal added to the nominal steady-state capacitance signal of the sensor, to provide a total capacitance signal. The amplitude and/or other aspects of the total capacitance signal may be analyzed to determine whether the device is moving across the skin, or dwelling at the same location. Thus, a capacitive sensor may be used as a dwell sensor  216 . Such analysis may include any suitable algorithms, e.g., comparing the signal to one or more threshold values. 
     As another example, the total capacitance signal may be analyzed to determine or estimate the speed of device  10  moving across the skin. Thus, a capacitive sensor may be used as a glide speed sensor  202 . As another example, the total capacitance signal may be analyzed to determine or estimate the displacement of device  10  moving across the skin. Thus, a capacitive sensor may be used as a displacement sensor  200 . 
     Usability Control 
     As discussed above regarding  FIG. 1 , device  10  may include control system  18  configured to control various controllable operational parameters of device  10  (e.g., operational aspects of radiation source  14 , scanning system  48 , etc.). In some embodiments, control system  18  may include a usability control system  133  configured to control the operation of device  10  (e.g., the generation and/or delivery of radiation) based on whether the device  10  is both (a) in contact with the skin and (b) sufficiently moving across the skin (e.g., based on a minimum displacement or glide speed of device  10 ). Usability control system  133  may be provided in addition to, or in place of, displacement-based control system  132 , depending on the particular embodiment. 
     In some embodiments, usability control system  133  may control the one or more operational aspects radiation source(s)  14 , such as for example, controlling the radiation mode of radiation source(s)  14 , controlling the on/off status of radiation source(s)  14 , controlling the timing of such on/off status (e.g., pulse trigger delay, pulse duration, pulse duty cycle, pulse frequency, temporal pulse pattern, etc.), controlling parameters of the radiation (e.g., wavelength, intensity, power, fluence, etc.), controlling parameters of optics  16 , controlling parameters of beam scanning system  48  (e.g., controlling the on/off status, rotational speed, direction of rotation, or other parameters of motor  120 ), and/or any other controllable operational parameters of device  10 . 
     In some embodiments, usability control system  133  may also provide feedback to the user via a display  32  and/or one or more other user interfaces  28  based on (a) the monitored skin contact and displacement status of device  10  and/or (b) the automatic control of one or more controllable operational parameters by system  133 . For example, system  133  may provide audio, visual, and/or tactile feedback to the user indicating data detected, or actions taken, by system  133 , e.g., feedback indicating whether device  10  is in contact with the skin and/or feedback indicating whether device  10  is sufficiently moving across the skin, or feedback indicating whether device  10  is both in contact with and sufficiently moving across the skin. 
     Usability control system  133  may include, utilize, or otherwise cooperate with or communicate with displacement-based control system  132  and/or any other control subsystems  52  discussed above with respect to  FIG. 2  (e.g., radiation source control system  128 , scanning system control system  132 , and user interface control system  134 , including user interface sensor control subsystem  140  and user input/feedback control subsystem  142 ), as well as control electronics  30 , any one or more sensors  26 , user interfaces  28 , and displays  32 . 
     In some embodiments, usability control system  133  may include one or more skin contact sensors  204 , one or more displacement sensors  200 , control electronics  30 , and one or more of: treatment radiation source  14 , scanning system  48 , and display  32 . In general, skin contact sensor(s)  204  and displacement sensor(s)  200  collects data regarding the contact and displacement of application end  42  of device  10  relative to the skin  40  and communicates such data to control electronics  30 , which analyzes the data and controls or provides feedback via one or more of treatment radiation source  14 , scanning system  48 , and display  32 . In some embodiments, control electronics  30  may also analyze particular user input received via one or more user interfaces  28  in conjunction with data received from sensor(s)  200  and  204 . For example, the appropriate control or feedback provided by control electronics  30  (e.g., as defined by a relevant algorithm  148 ) may depend on the current operational mode and/or other settings selected by the user. 
     In some embodiments, usability control system  133  controls the starting and stopping (e.g., interruption) of radiation delivery based on signals from one or more skin contact sensors  204  and one or more displacement sensors  200  indicating whether application end  42  of device  10  is in contact with the skin and moved across the skin with sufficient displacement to allow generation and delivery of radiation. In other words, usability control system  133  may be configured to start/stop the delivery of radiation based on whether device  10  is being properly positioned and moved for a dermatological treatment. 
     In some embodiments, usability control system  133  defines different standards for starting/stopping radiation delivery based on the particular operation situation. For example, usability control system  133  may define a first set of conditions required to initiate radiation delivery (e.g., to turn on radiation source  14 ) and a different second set of conditions required to maintain radiation delivery after initiation. As another example, usability control system  133  may define a first set of conditions required to initiate radiation delivery (e.g., to turn on radiation source  14 ), a different second set of conditions required to maintain radiation delivery after initiation, and a different third set of conditions required to restart radiation delivery after an interruption of radiation delivery. 
     In an example embodiment, device  10  includes two displacement sensors  200   a  and  200   b  and four skin contact sensors  204   a - 200   d  at the application end  42  of device  10 , e.g., in the example arrangement shown in  FIG. 50 . Usability control system  133  may define conditions for initiating, maintaining, interrupting, and restarting radiation delivery as follows: 
     (1) Generation of the initial pulse/beam of a treatment session requires (a) signals from all four skin contact sensors  204  independently indicating contact with the skin, and (b) signals from both displacement sensors  200  independently indicating that devices  10  has been moved a predetermined displacement across the skin. 
     (2) After the initial pulse, continued pulsing/beam delivery requires (a) signals from at least one of the two “bottom” skin contact sensors  204   a  and  204   b  (see  FIG. 50 ) indicating contact with the skin, and (b) signals from at least one of the two “top” skin contact sensors  204   c  and  204   d  (see  FIG. 50 ) indicating contact with the skin, and (c) signals from at least one of two displacement sensors  200   a  and  200   b  independently indicating that devices  10  has been moved a predetermined displacement across the skin. 
     (3) If any of the conditions in condition set (2) are violated (i.e., any of conditions (2)(a), (2)(b), or (2)(c)), system  133  interrupts pulsing immediately or substantially immediately. System  133  then continues to apply condition set (2) to determine whether to re-start pulsing. However, if any of the conditions in condition set (2) is violated for a consecutive duration of one second, system  133  instead applies the more stringent conditions of condition set (1) in order to re-start pulsing. 
     This algorithm using different sets of conditions for initiating, maintaining, interrupting, and restarting the radiation delivery may allow some imperfect contact and/or sensing interface between sensors  200 / 204  and the skin (e.g., when gliding over boney features or other contoured features of the body), without discontinuing radiation delivering due to such imperfect contact. In other words, once the device has initially determined proper skin contact and device movement, the algorithm relaxes the skin contact/displacement detection standards to account for some imperfect contact with the skin for brief durations (e.g., less than one second). This may improve the practical “usability” of the device  10 , so that the start/stop control of radiation delivery may better match the actual use of device  10  in a real world application. 
       FIG. 49  illustrates an example flowchart of the algorithm discussed above, which may be stored as an algorithm  148  and implemented by usability control system  133 , e.g., using any suitable control electronics  30 . System  133  first determines whether the current control decision regards an initial pulse by radiation source  14 , at step  572 . If so, at step  574 , system  133  determines whether all contact sensors  204   a - 204   d  currently detect contact and all (both) displacement sensors  200   a - 200   b  currently detect a predetermined minimum displacement of device  10  across the skin. If so, system  133  begins pulsing the radiation source  14  at step  576 . If not, system  133  continues to receive and analyze signals from sensors  200  and  204  until the conditions at step  574  are met. 
     After the initial pulse is delivered, system  133  applies less stringent conditions to continue pulsing. In particular, at step  578 , system  133  determines whether at least one bottom contact sensor  204   a - 204   b  currently detects skin contact, and at least one top contact sensor  204   c - 204   d  currently detects skin contact, and at least one displacement sensor  200   a - 200   b  currently detects the predetermined minimum displacement of device  10  across the skin. If these conditions are met, system  133  continues pulsing, indicated at  580 . In one or more of these conditions are met, system  133  interrupts pulsing at  582 . If the violation of the condition(s) at step  578  has continued consecutively for one second, system  133  reverts back to the more stringent standards at step  574 , for re-starting pulsing. If the violation of the condition(s) at step  578  has not yet continued for one second, system  133  may continue to apply the less stringent standards at step  578 , for re-starting pulsing. 
     It should be understood that algorithm  570  is an example only, and that usability control system  133  may employ any other suitable control algorithm or algorithms. 
       FIG. 50  an end view of example application end  42  (e.g., as seen by the skin) of device  10 , e.g., for use with displacement-based control system  132  and/or usability control system  133 , according to one embodiment. In this example, application end  42  is elongated in the scan direction and includes (a) an elongated optical element  16  or window  44  through which scanned beams  114  are delivered to the skin, (b) four capacitive skin contact sensors  204   a - 204   d , (c) a pair of displacement sensors  200   a  and  200   b , each configured to interface with the skin through an optic  16  or window  44 . In other embodiments, one or more displacement sensors  200  (and/or other types of sensors) interface with the skin through the same optic  16  or window  44  as scanned beams  114 . 
     In this embodiment, skin contact sensors  204   a - 204   d  are provided near the corners of application end  42 . This arrangement allows for the detection of any edge of application end  42  being lifted off the skin. For example, sensors  204   a  and/or  204   b  can detect if edge E 1  is lifted off the skin, sensors  204   c  and/or  204   d  can detect if edge E 2  is lifted off the skin, sensors  204   a  and/or  204   c  can detect if edge E 3  is lifted off the skin, and sensors  204   b  and/or  204   d  can detect if edge E 4  is lifted off the skin. In other embodiments, any other number and arrangement of skin contact sensor(s)  204  may be provided. As discussed above, contact sensors  204  may be capacitive sensors or any other suitable type of sensors for detecting contact with the skin. 
     Each optic  16  or window  44  may provide any suitable optical path for delivering light to and/or receiving reflected light from the skin. Alternatively, any sensor  26  and/or the beam delivery aperture may be open to the air, i.e., without an optic  16  or window  44  at application end  42 . In the illustrated example, 12 scanned beams  114  pass through optic  16  or window  44  in a linear row pattern extending in the scan direction. Thus, optic  16  or window  44  may be sized and shaped based on the locations of the 12 scanned beams  114 . In an example embodiment that uses an output window  44 , the window  44  may be rectangular with dimensions of about 20 mm length (L W ) by 2 mm width (W W ), with a width of about 3 mm (W S ) on each side of window  44 , for locating various sensors  26  and/or rollers, and/or other features. In an example embodiment that uses an output optic  16 , the optic  16  may comprise a rod lens having a diameter of about 5 mm and length (L W ) of about 20 mm. 
     Eye Safety 
     Some embodiments of device  10  provide eye safe radiation, e.g., by delivering scanned, divergent beams  114  from the application end  42  of the device, and/or using an eye safety control system including one or more sensors  26  including one or more eye safety sensors  214  and/or other types of sensors  26 , and/or by any other suitable manner. For example, in some embodiments or settings, device  10  meets the Class 1M or better (such as Class 1) eye safety classification per the IEC 60825-1, referred to herein as “Level 1 eye safety” for convenience. In other embodiments or settings, the device exceeds the relevant Accessible Emission Limit (AEL) (for 1400-1500 nm or 1800-2600 nm wavelength radiation) by less than 50%, referred to herein as “Level 2 eye safety” for convenience. In still other embodiments or settings, the device exceeds the relevant AEL (for 1400-1500 nm or 1800-2600 nm wavelength radiation) by less than 100%, referred to herein as “Level 3 eye safety” for convenience. The Accessible Emission Limit (AEL), as specified in IEC 60825-1, e.g., for 1400-1500 nm or 1800-2600 nm wavelength radiation, is discussed below. In other embodiments or settings, device  10  meets the next highest eye safety classification after Class 1M per the IEC 60825-1, i.e., Class 3B, referred to herein as “Level 4 eye safety” for convenience. 
     Such levels of eye safety may be provided based on a combination of factors, including for example, one or more of the following: (a) the scanning of an input beam, (b) the divergence of delivered beams (e.g., in embodiments that use laser diode radiation source(s)), (c) the emitted power, (d) the wavelength of the delivered beams, (e) the pulse duration, and (f) the total energy per delivered beam. Thus, in some embodiments, one, some, or all of such factors may be selected or adjusted to provide Level 1, Level 2, Level 3, or Level 4 eye safety, as defined above. 
     In the wavelength ranges of 1400-1500 nm and 1800-2600 nm (e.g., for providing certain fractional treatments), corneal damage is typically the primary concern for eye safety. In some embodiments that radiate in such wavelength ranges using a laser diode source, the beam scanning and divergence inherently provided by a scanned divergent laser diode source, alone or in combination with other eye safety features, may provide a desired eye safety for device  10 . For example, it may provide Level 1, Level 2, Level 3, or Level 4 eye safety, depending on the other selected parameters. An analysis of relevant issues is discussed below. 
     A scanned, divergent, intense-radiation source (e.g., certain laser diode sources) may provide eye safe radiation. For certain wavelengths greater than 1400 nm (including, e.g., typical wavelengths used in fractional laser treatment), the radiation source is greatly attenuated by the water absorption in the eye anterior chamber. Thus, there is substantially little or no retinal hazard in this wavelength range. The emission limit is determined by the potential corneal damage. Moreover, since there is no focusing effect by the eye lens, the hazard is further minimized by beam scanning to avoid compounding the laser energy on the corneal surface. For Class 1M eye safety classification per IEC 60825-1, the Accessible Emission Limit (AEL) in the wavelength range of 1400 to 1500 nm and 1800 to 2600 nm is described by a simple equation in Table 4 of IEC 60825-1:2007:
 
AEL=4.4 t   0.25  mJ  Equation 1
 
     For a scanned beam system, the AEL energy is measured at 100 mm from the source with a circular aperture of 1 mm in diameter (Condition 3 measurement setup described in Table 11 of IEC 60825-1:2007, applicable for scanned beams viewed by unaided eye). In this equation, t (in unit of seconds) is the source pulse duration in the range of 1 ms to 350 ms. For example embodiments that include a scanned laser diode source, this pulse duration may be in the range of 1 to 10 ms. The corresponding AEL is 0.8 to 1.4 mJ. 
     The actual source AE (Accessible Energy) can be estimated for given scanned beam characteristics including the beam&#39;s divergence in both axes. It can also be measured experimentally with the appropriate aperture stop (1-mm wide) and measurement distance (100-mm from the source). The AE at a distance 100-mm from the treatment aperture is given by (this is approximately correct for a Gaussian beam from a diffraction limited laser):
 
AE=2.5×10 −5   Q /[tan(Φ F /2)tan(Φ S /2)]mJ  Equation 2
 
     where Q (in unit of mJ) is the source energy at the treatment plane, and Φ F  and Φ S  are the beam divergence in the fast and slow axis, respectively. To achieve the Class 1M eye safety classification, AE must be lower than the AEL for the corresponding pulse duration. 
     Table 1 below provides several example configurations and device settings for providing Level 1 eye safety (Class 1M or better per standard IEC 60825-1) for certain embodiments of device  10  that provide pulsed radiation in the 1400-1500 nm or 1800-2600 nm wavelength ranges (e.g., for fractional treatment) using a scanned laser diode source  14 , wherein each pulse is scanned to a different location. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Example 
                   
                 Example 
               
               
                   
                   
                 Embodiment 
                   
                 Embodiment 
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                 Parameter 
                 Design 1 
                 Design 1 
                 Design 2 
                 Design 2 
               
               
                   
               
             
            
               
                 Configuration 
                 No 
                 No 
                 With 
                 With 
               
               
                   
                 downstream 
                 downstream 
                 downstream 
                 downstream 
               
               
                   
                 fast-axis rod 
                 fast-axis rod 
                 fast-axis rod 
                 fast-axis rod 
               
               
                   
                 lens 
                 lens 
                 lens 
                 lens 
               
               
                 Radiation source 
                 scanned laser 
                 scanned laser 
                 scanned laser 
                 scanned laser 
               
               
                   
                 diode 
                 diode 
                 diode 
                 diode 
               
               
                 Radiation mode 
                 Pulsed (one 
                 Pulsed (one 
                 Pulsed (one 
                 Pulsed (one 
               
               
                   
                 pulse per 
                 pulse per 
                 pulse per 
                 pulse per 
               
               
                   
                 delivered 
                 delivered 
                 delivered 
                 delivered 
               
               
                   
                 beam) 
                 beam) 
                 beam) 
                 beam) 
               
               
                 wavelength 
                 1400-1500 nm 
                 1400-1500 nm 
                 1400-1500 nm 
                 1400-1500 nm 
               
               
                   
                 or 1800-2600 nm 
                 or 1800-2600 nm 
                 or 1800-2600 nm 
                 or 1800-2600 nm 
               
               
                 beam divergence 
                 0.3°-2° fast 
                 1.5° fast axis 
                 4°-8° fast axis, 
                 6° fast axis 
               
               
                 at skin surface 
                 axis, 
                 3° slow axis 
                 2°-4° slow axis 
                 3° slow axis 
               
               
                 (fast axis, slow 
                 2°-4° slow 
               
               
                 axis) 
                 axis 
               
               
                 Pulse/delivered 
                   3-10 
                 about 8 
                   3-10 
                 about8 
               
               
                 beam duration 
               
               
                 (ms) 
               
               
                 Power (W) 
                 0.5-3 
                 about 1.5 
                  0.5-3 
                 about 1.5 
               
               
                 Total energy per 
                   5-15 
                 about 12 
                   5-15 
                 about 12 
               
               
                 pulse/delivered 
               
               
                 beam (mJ) 
               
               
                 AEL (mJ) 
                 1.0-1.4 
                 about 1.3 
                  1.0-1.4 
                 about 1.3 
               
               
                 AE (mJ) 
                 0.2-8.2 
                 about 0.9 
                 0.05-0.6 
                 about 0.2 
               
               
                 Eye safety 
                 Class 1M for 
                 Class 1M 
                 Class 1M 
                 Class 1M 
               
               
                 classification 
                 AE &lt; AEL 
               
               
                   
               
            
           
         
       
     
     Because certain embodiments or device settings may provide Level 1, Level 2, Level 3, or Level 4 eye safety based on the appropriate selection of parameters discussed above, in some such embodiments an eye safety sensor or system may be omitted. However, some such embodiments, even those providing Level 1 eye safety, may include one or more eye safety sensors (e.g., one or more eye safety sensors  214  described below) and/or an eye safety system to provide redundancy, to meet particular regulatory standards, or for other reasons. 
     In at least some embodiments additional eye safety is provided by incorporating one or more skin contact sensors  204  that enable pulsing of the radiation source  14  only when device  10  in contact with the skin. Thus, in such embodiments, the likelihood of corneal eye injury may be reduced or substantially eliminated unless device  10  is literally pressed to the eye surface. 
     Eye Safety Sensor 
     In some embodiments, device  10  includes an optical eye safety sensor  214  configured to detect the presence of a cornea (or other eye tissue or feature) near a treatment output aperture of device  10 , in order to help prevent unintended eye exposure to light from the treatment radiation source  14 . For example, optical eye safety sensor  214  may be configured to distinguish between the presence of skin and the cornea, and enable device  10  to treat only the intended treatment area  40 . Eye safety sensor  214  may be especially important for infrared treatment light of wavelength greater than 1400-nm, for which the eye injury risk is primarily in the cornea or for UV, visible, and/or near-IR where retinal hazards exist. In some embodiments, optical eye safety sensor  214  is relatively low cost, compact, easily packaged within a handheld enclosure (e.g., small and lightweight), and assembled from commonly available parts. Another example embodiment of an eye safety sensor is an imaging sensor with pattern recognition for shape, color, or other feature of the eye. 
       FIG. 51A  illustrates an example optical eye safety sensor  214 , according to certain embodiments. Optical eye safety sensor  214  may include a light source  510 , a light detector  512 , detector optics  520 , relay optics  522  (in some embodiments), and a microcontroller  530 . 
     Light source  510  may be a light-emitting diode (LED) or any other suitable light source. Light source  510  may be selected for showing fine details in the surface of human skin. Thus, a wavelength may be selected that penetrates a relatively shallow depth into the skin before being reflected. For example, light source  510 A may be a blue LED having a wavelength of about 560 nm, or a red LED having a wavelength of about 660 nm, or an infrared LED having a wavelength of about 940 nm. Red or infrared wavelength LEDs are relatively inexpensive and work well in practice. Alternatively, a semiconductor laser could be used. 
     Light detector  512  may be a photodiode, phototransistor, or other light detector. In some embodiments, a phototransistor has sufficient current gain to provide a directly usable signal, without requiring additional amplification. Light detector optics  520 , e.g., a half-ball lens, may be coupled to or carried with light detector  512 . Light detector optics  520  may be configured to allow light detector  512  to “view” a target surface location. 
     Further, in some embodiments, sensor  214  may include relay optics  522  for relaying light from light source  510  and/or relay optics  522  for relaying reflected light to detector  512 . Relay optics  522  may be used to relay light for any desired distance, such that one, some, or all of light source  510 , detector optics  520 , and/or detector  512  may be located at any desired distance from an aperture  526  in housing  24  that may be configured to be positioned on or near the skin surface  38  during use. Also, microcontroller  530  and/or other electronics associated with sensor  214  may be located at any distance from aperture  526  and/or from the other components of sensor  214  (e.g., light source  510 , detector  512 , detector optics  520 , and optional relay optics  522 ). In some embodiments, locating components of sensor  214  away from aperture  526  may reduce or minimize the space occupied by sensor  214  at application end  42  of device  10 , which may allow for a reduced or minimized size of application end  42 , which may be desirable or advantageous. 
     In other embodiments, components of sensor  214  may be located near aperture  526  (e.g., in the application end  42  of device  10 ), such that relay optics  520  are not included. 
     Light source  510  may be oriented to illuminate a surface (e.g., skin surface  38 ) at a very low angle of incidence (e.g.,  0  shown in  FIG. 51B  may be between about 5 and 40 degrees), while detector  512  may be aligned at a normal or near-normal angle of incidence relative to the illuminated surface. 
     Microcontroller  530  may be configured to drive light source  510  (e.g., an LED) with a direct or modulated current, record a signal  524  from detector  512  using an integrated ADC  532 , and analyzes the amplitude of the recorded detector signal  524  to determine if the surface below detector  512  is skin  40  or cornea  500 . 
     The signal  524  from detector  512  may be referred to as a “reflectance feedback signal.” The amplitude of the reflectance feedback signal  524  corresponds to the intensity of reflected light from light source  510  received by detector  512 : the more light from light source  510  that is reflected into detector  512 , the higher the amplitude of reflectance feedback signal  524 . As discussed below, due to the configuration of light source  510  and detector  512 , skin (which is relatively diffuse) reflects more of light from light source  510  into detector  512  than the cornea (which is relatively specular). Thus, microcontroller  530  may analyze the amplitude of reflectance feedback signal  524  (e.g., using threshold or window comparisons) to determine whether the surface below detector  512  is skin  40  or cornea  500 . 
     Signals from microcontroller  530  indicating whether a treatment window  44  of device is located above skin or the cornea may be used by control systems  18  for controlling one or more controllable operational parameters of device  10 . 
     For example, treatment (e.g., delivery of radiation to a treatment area  40 ) may be initiated, such as to begin a treatment session, or re-initiated after an interruption during a treatment session if microcontroller  530  detects a “skin presence,” e.g., by determining that reflectance feedback signal  524  is above a predefined skin/cornea threshold or within a predefined reflectance window corresponding with skin. In such situation, control systems  18  may enable or power on treatment radiation source  14  (or control other aspects of device  10 ) to begin radiation delivery to the treatment area  40 . The treatment may continue as long as microcontroller  530  continues to detect a skin presence. The treatment may be interrupted upon detection of a “possible cornea presence” or upon other treatment interrupting events. 
     If microcontroller  530  determines that reflectance feedback signal  524  is below the predefined skin/cornea or outside the reflectance window corresponding with skin, microcontroller  530  may detect a “possible cornea presence” (which is essentially a detection of a non-skin surface, which could be a cornea, other non-diffuse surface, or lack of a target surface, for example). Control systems  18  may disable treatment radiation source  14  (or control other aspects of device  10 ) in response to a possible cornea presence detected by microcontroller  530 , in order to prevent a possible unintended eye exposure (and possible eye damage). 
     The operation of sensor  214  is described below with reference to  FIGS. 51B-51D .  FIG. 51B  illustrates light source  510  and two different positions of detector  512 .  FIGS. 51C and 51D  illustrate the local surface normal directions for example corneas of different shapes. 
     Detector  512  receives a larger amount of reflected light (and thus generates a larger amplitude of signal  524 ) from diffuse surface materials, due to light scattering, than from smoother, more specular reflection materials. Skin is relatively diffuse, while the corneal surface is generally smooth and specular, such that the corneal surface has a much lower diffuse component of reflection than the skin. This difference can be used to determine whether detector  512  is positioned over an area of skin  40  or over the cornea  500 . 
     This technique of discriminating between diffuse and specular materials using a single beam source  510  and single detector  512  may assume that the angles between the target surface normal and both the beam source  510  and detector  512  are known at least to an extent. In particular, the angles at which beam source  510  and detector  512  are aligned relative to the target surface may be selected such that the reflectance feedback signal  524  can be reliably used to distinguish reflection off the skin from reflection off the cornea, for a known range of corneal curvatures, as discussed below with respect to  FIGS. 51C and 51D . 
     In general, the local surface normal vector of a surface (e.g., skin or corneal surface) will vary relative to a larger-scale average surface normal, depending on the local curvature of the surface. For example, near the edge of the cornea, the local surface normal will be at least several degrees offset from the normal vector at the center of the cornea, because the cornea is a curved surface. 
     Assume a light beam source illuminates a surface at an incidence of near-grazing (˜0 degrees) and a detector views this surface at near normal incidence (˜90 degrees). For less curved surfaces, the local surface normals are relatively close to 90 degrees, as shown in  FIG. 51C . In an extreme case shown in  FIG. 51D , in which curvature provides a local surface normal of 45 degrees, a specular reflection propagates directly into the detector. It may be assumed for the purposes of sensor  214  that the exposed corneal surface forms an angle of less than 45 degrees with the larger surface normal of the face (i.e., skin adjacent the eye), such that a direct specular reflection from beam source to detector does not occur for any practical configuration of sensor  214 /device  10  relative to the face. It is also known that for a normal eye, the most extreme angle near the corneal edge is less than 40 degrees. (See, e.g., James D. Doss, “ Method for Calculation of Corneal Profile and Power Distribution”, Arch Ophthalmol , Vol. 99, July 1981). Moreover, this angle quickly decreases to near 20 degrees within 60% of the central cornea region, i.e., the curvature is not large near the cornea center. Therefore, for the central 60% cornea region, the specular reflection from the cornea will not be intercepted by the detector with a large margin. 
     Thus, assuming light source  510  is arranged at a sufficiently low angle of incidence (e.g., θ shown in  FIG. 51B  between about 5 and 40 degrees), for all practical cases the cornea will not reflect the light from light source  510  directly into detector  512 . Thus, for all practical cases, the cornea will reflect less light from light source  510  into detector  512  than will the skin. Thus, for practical cases, the cornea can be distinguished from skin, assuming the proper signal amplitude thresholds are utilized by microcontroller  530 . Thus, to summarize, assuming the proper orientation of light source  510  and detector  512 , as well as the proper selection of threshold(s) for comparing the amplitude of reflectance feedback signal  524 , sensor  214  is able to reliably discriminate between the skin and the cornea, especially for the central cornea region which may be the most important for vision. 
     It has been shown experimentally that the scattering coefficient of skin dermis μm s   _   skin  is substantially greater than that of the cornea μm s   _   cornea . In particular, the scattering coefficient of skin dermis μm s   _   skin ≈60 cm −1  for 500-nm wavelength (see Steven L. Jacques, “ Skin Optics”, Oregon Medical Laser Center News , January 1998), whereas the scattering coefficient of skin dermis μm s   _   cornea ≈10 cm −1  for 500-nm wavelength (see Dhiraj K. Sardar, “ Optical absorption and scattering of bovine cornea, lens, and retina in the visible region”, Laser Med. Sci.,  24(6), November 2009). Based on these respective scattering coefficients, the expected diffused reflectance of the cornea is about 8%, while the expected diffused reflectance for a typical Fitzpatrick Type I to VI skin ranges from 70% to 10% respectively. Thus, for most skin types, the reflectance contrast is large enough discriminating the cornea from the skin, again assuming the proper comparison thresholds or windows are utilized by sensor  214 . 
     Multi-Sensor Eye Safety System 
     In some embodiments, device  10  includes a multi-sensor control/safety system that includes one or more eye safety sensor  214  and one or more skin contact sensors  204 . 
       FIG. 52  illustrates an example multi-sensor control/safety system  550  that includes one or more eye safety sensor  214  and one or more skin contact sensors  204  arranged on or near device application end  42 . System  550  combines the functionality of eye safety sensor  214  and skin contact sensor(s)  204  to provide more reliable and/or redundant eye safety functionality as compared to eye safety sensor  214  or skin contact sensor(s)  204  acting alone. 
     System  550  may configured to control device  10  (e.g., turn treatment radiation source  14  on/off) based on independent determinations made by eye safety sensor  214  and skin contact sensor(s)  204 , in any suitable manner. The independent determinations made by eye safety sensor  214  and skin contact sensor(s)  204  may be based on comparisons of signals detected by such sensors to respective thresholds, referred to herein as “independent determination thresholds.” 
     For example, system  550  may trigger a control signal to turn on treatment radiation source  14  if either (a) eye safety sensor  214  determines a “skin presence” (discussed above), independent of any determinations or signal analysis by contact sensor(s)  204 , or (b) all contact sensors  204  determine a contact status with the skin, independent of any determinations or signal analysis by eye safety sensor  214 . Thus, system  550  may trigger a control signal to turn off treatment radiation source  14  only if both (a) eye safety sensor  214  determines a “possible cornea presence” (discussed above), independent of any determinations or signal analysis by contact sensor(s)  204 , and (b) at least one contact sensor  204  determines a non-contact status with the skin, independent of any determinations or signal analysis by eye safety sensor  214 . 
     Alternatively, system  550  may trigger a control signal to turn on treatment radiation source  14  only if both (a) eye safety sensor  214  determines a skin presence (discussed above), independent of any determinations or signal analysis by contact sensor(s)  204 , and (b) all contact sensors  204  determine a contact status with the skin, independent of any determinations or signal analysis by eye safety sensor  214 . Thus, system  550  may trigger a control signal to turn off treatment radiation source  14  if either (a) eye safety sensor  214  determines a possible cornea presence, independent of any determinations or signal analysis by contact sensor(s)  204 , or (b) any contact sensor  204  determines a non-contact status with the skin, independent of any determinations or signal analysis by eye safety sensor  214 . 
     Alternatively or in addition, system  550  may be configured to control device  10  (e.g., turn treatment radiation source  14  on or off) based on inter-dependent analysis of signals from eye safety sensor  214  and signals from skin contact sensor(s)  204 . For example, system  550  may utilize algorithms that analyze signals detected by eye safety sensor  214  (e.g., reflectance feedback signal  524  from detector  512 ) and signals detected by contact sensor(s)  204  (e.g., signal  552  detected by contact sensor(s)  204 ) to determine whether to trigger a particular control signal. For example, such algorithms may incorporate thresholds that are lower than the independent determination thresholds discussed above. Such thresholds are referred to herein as “inter-dependent sensor analysis thresholds.” 
     To illustrate by example, system  550  may specify the following independent determination thresholds:
         (a) 10 mV eye safety threshold: eye safety sensor  214  determines a possible cornea presence if the amplitude of reflectance feedback signal  524  falls below 10 mV, and   (b) 50 pF contact sensor threshold: contact sensor  204  determines a non-contact status if the amplitude of contact sensor signal  552  falls below 50 pF.       

     Further, system  550  may specify the following inter-dependent sensor analysis thresholds:
         (a) 15 mV eye safety threshold for reflectance feedback signal  524 , and   (b) 70 pF contact sensor threshold for signal  552 .       

     System  550  may utilize an algorithm  154  that incorporates the inter-dependent sensor analysis thresholds (15 mV and 70 pF). For example, an algorithm may specify a control signal to turn off treatment radiation source  14  if both (a) reflectance feedback signal  524  falls below 15 mV and (b) contact sensor signal  552  falls below 70 pF. 
     As another example of controlling device  10  based on inter-dependent analysis of signals from eye safety sensor  214  and signals from skin contact sensor(s)  552 , an algorithm  154  may calculate an index, referred to herein as an “eye safety factor index,” or ESF index from reflectance feedback signal  524  and contact sensor signal  552 . The algorithm may weight reflectance feedback signal  524  and contact sensor signal  552  in any suitable manner. An example algorithm is provided as equation (1):
 
ESF index=signal 524 amplitude* W 1+signal 552 amplitude* W 2  (1)
         where W1 and W2 represent any suitable constants (including 0).
 
Another example algorithm is provided as equation (2):
 
ESF index=(signal 524 amplitude+ C 1)*(signal 552 amplitude+ C 2)  (2)
   where C1 and C2 represent any suitable constants (including 0).       

     Any other suitable algorithms may be used for calculating an ESF index based on reflectance feedback signal  524  and contact sensor signal  552 . 
     ESF index may then be compared to a predefined threshold to determine whether to trigger a particular control signal (e.g., to turn off treatment radiation source  14 ), or compared to multiple different predefined thresholds for triggering different control signals. Such algorithms (using the same or different threshold values) may be used for triggering any suitable control signals, such as control signals for turning on treatment radiation source  14 , turning on treatment radiation source  14 , changing the current treatment mode, or adjusting any controllable operational parameter of device  10 . 
       FIG. 53  illustrates an example method  600  for controlling device  10  (e.g., controlling treatment radiation source  14 ) using a multi-sensor control/safety system  550 , according to certain embodiments. At step  602 , a user prepares for a treatment session by selecting a treatment mode and/or other treatment parameters, and places the application end  42  of device  10  against the skin. 
     At step  604 , system  550  determines whether the application end  42  is correctly positioned against the skin for treatment, e.g., using any of the techniques discussed above or any other suitable technique. 
     If system  550  determines that the application end  42  is correctly positioned against the skin for treatment, system  550  may generate a control signal for beginning a treatment session automatically or upon a defined user input (e.g., pressing a treatment button), as indicated at step  606 . Control systems  18  may also generate feedback to the user indicating that treatment has been initiated or that treatment is ready for initiation upon the defined user input (e.g., pressing a treatment button). 
     Device  10  may then activate radiation source  14  to generate beam  108  for delivery to the skin  40  as delivered beams  114  to generate treatment spots  70 , as indicated at step  608 . The user may operate device  10  in a gliding mode or a stamping mode, depending on the configuration and/or selected treatment mode of device  10 . 
     During the treatment, system  550  continually or repeatedly determines whether the application end  42  is still correctly positioned against the skin for treatment, as indicated at step  610 . As long as system  550  determines that application end  42  is correctly positioned against the skin for treatment, system  550  may continue to generate control signals for continuing the treatment session (i.e., such that control systems  18  continue to deliver beams  114  to generate treatment spots  70  on the skin  40 ), as indicated at step  612 . 
     However, during the treatment, if system  550  determines that application end  42  is not correctly positioned against the skin for treatment (e.g., if system  550  determines that application end  42  is located over the cornea or moved out of contact with the skin), system  550  may generate a control signal for automatically stopping or interrupting the treatment session, e.g., by turning off or disabling treatment radiation source  14 ), as indicated at step  614 . Control systems  18  may also generate feedback, e.g., audible or visual feedback, to the user indicating the status of device  10 . For example, control systems  18  may provide general feedback indicating that the treatment has been stopped or interrupted, or may provide more specific feedback indicating the reason that the treatment has been stopped or interrupted, such as feedback distinguishing between eye detection, non-contact detection, and device malfunction, for example. 
     System  550  may continue to monitor the positioning of application end  42  at step  616 . If system  550  determines that application end  42  has again become correctly positioned against the skin for treatment, system  550  may resume the treatment session, e.g., by generating a control signal to resume treatment (e.g., by turning on treatment radiation source  14 ), as indicated at step  618 , and resuming the generation of treatment spots  70  in the skin, as indicated by the method returning to step  608 . 
     The treatment session may end upon reaching a treatment delimiter (such as discussed above regarding  FIG. 47 ), or after a predefined time, or based on any other parameters defining the treatment session. It should be understood that this example and  FIG. 53  can apply to sensors other than contact sensor in a similar manner. 
     Calibration of Eye Safety Sensor 
     In some embodiments, eye safety sensor  214  can be individually calibrated to the current user of device  10 .  FIG. 54  illustrates an example method  650  for calibrating eye safety sensor  214  for one or multiple users. A calibration process is performed at steps  652 - 660 . At step  652 , a user positions the application end  42  of device  10  against the user&#39;s skin, e.g., upon instruction from device  10 . Device  10  may instruct the user to position application end  42  against a certain part of the body, e.g., the face or back of the hand. Sensor  214  is activated and records a reflectance feedback signal  524  at step  654 . At step  656 , the user may move the application end  42  of device  10  across the skin, e.g., upon instruction from device  10 . Sensor  214  may continue to record reflectance feedback signal  524  at various locations of application end  42  on the skin, at step  658 . 
     At step  660 , microcontroller  530  may analyze signal  524  recorded at steps  654 ,  658  to calibrate sensor  214 . For example, microcontroller  530  may execute one or more algorithms to determine one or more appropriate threshold values (e.g., threshold voltages) for distinguishing between skin and the cornea, e.g., for determining a “skin presence” or “possible cornea presence,” as discussed above. Such threshold values may be stored by sensor  214  or control system  18 . 
     At step  662 , the same user or a different user may initiate device  10  for a treatment session. The user may identify him or herself via a user interface  18 , e.g., by scrolling and selecting from a list of names, or entering a new name, at step  664 . Device  10  may then determine whether eye safety sensor  214  has been calibrated for that user, and if so, access the skin/cornea determination thresholds stored for that user, at step  666 . If the user is a new user or eye safety sensor  214  has not been calibrated for that user, device  10  may calibrate sensor  214  for that user to determine and store skin/cornea determination thresholds for that user, at step  668  (e.g., by leading the user through the calibration process of steps  652 - 660 ). 
     After the skin/cornea determination thresholds for the user have been accessed (or in the case of a new user, determined and stored), the user may select various operational parameters and begin a treatment session using device  10 . During the treatment session, at step  670 , eye safety sensor  214  may continually or repeatedly monitor the surface under application end  42  using the user-specific thresholds accessed at step  666  or  668 . 
     In other embodiments, device  10  may require eye safety sensor  214  to be recalibrated before each treatment session. 
     Dual-Function Sensors 
     In some embodiments, in addition to providing eye safety functionality, eye safety sensor  214  may also be used as a displacement sensor, operating in a similar manner as discussed above regarding single-pixel displacement sensor  200 A,  200 B, or  200 C shown in  FIGS. 40A-40C . The functionality of eye safety sensor  214  and a displacement sensor  200 A/ 200 B/ 200 C may be integrated into a single sensor  200 / 214 . Thus, a single radiation source and single detector may be used to provide both the eye safety and displacement monitoring functions described above. The integrated eye safety/displacement sensor  200 / 214  includes one or more microcontrollers or other processors for providing the functionality of both sensors. 
     In other embodiments, device  10  may include both eye safety sensor  214  and one or more displacement sensors  200  (e.g., one or more single-pixel displacement sensors  200 A/ 200 B/ 200 C and/or one or more multi-pixel displacement sensors  200 D), wherein eye safety sensor  214  provides (in addition to its eye safety functionality) device displacement monitoring functionality to supplement or provide a backup to the displacement sensor(s)  200 A/ 200 B/ 200 C/ 200 D. 
     Radiation Pulse and Scanning Element Motor Control 
     In some embodiments, device  10  includes a pulsed laser radiation source  14  and a motor/pulse control system  139  configured to monitor and control the operation of pulsed laser radiation source  14  and beam scanning system  48 , e.g., scanning system motor  120 . Motor/pulse control system  139  may combine aspects of any of the various control systems discussed above, e.g., radiation source control system  128 , scanning system control system  130 , displacement-based control system  132 , usability control system  133 , user interface control system  134 , and temperature control system  136 . For example, motor/pulse control system  139  may control pulsed laser radiation source  14  to control the pulse duration, pulse on time, pulse off time, trigger delay time, duty cycle, pulse profile, or any other parameters of generated pulses; and may control scanning system motor  120  of scanning system  48  (e.g., to control the speed, position, etc. of a rotating beam-scanning element  100 ), etc. Motor/pulse control system  139  may control such parameters based on signals from various sensors  26  and/or by monitoring the rotation and/or position of an encoder  121 , which may be arranged to indicate the rotation and/or position of a rotating beam-scanning element  100 . An example of such encoder  121  is shown in  FIGS. 68A and 68B , discussed below. 
     Motor/pulse control system  139  may provide various control redundancies, which may be designed, for example, to ensure accuracy of energy dose per laser pulse, as well as to provide eye safety and skin safety aspects. 
       FIG. 55  illustrates components of an example motor/pulse control system  139 , according to an example embodiments. Motor/pulse control system  139  may include a number of sensors  26  for providing input to control electronics  30  for controlling laser  14  and scanning system motor  120 , which is configured to drive the rotation of beam scanning element  100  and encoder  121 . 
     Sensors  26  of system  139  may include, for example, four independent contact sensors  204   a - 204   d  for detecting skin contact, two independent displacement sensors  200   a  and  200   b  for detecting displacement of device  10  relative to the skin, a temperature sensor for detecting a temperature of or related to the laser  14  (e.g., a temperature of laser package  250  or heat sink  36 ), an optical encoder sensor  203  for monitoring the speed of the scanning system motor  120  and for detecting the rotation and/or position of rotating scanning element  100  (by monitoring encoder  121 ). 
     Control electronics  30  may include a main processor or controller  144 A, an independent secondary processor or controller  144 B, and executable logic or algorithms  148  stored in any suitable storage medium  146 . Main controller  144 A may generally be configured to control the various parameters of system  139 , while secondary controller  144 B may provide independent error checking for integrity verification, thus providing redundancy, e.g., to provide an additional aspect of safety. 
     The speed of scanning system motor  120  and the trigger timing (e.g., trigger delay time) for each individual laser pulse must be well coordinated depending on multiple factors, including the desired laser pulse duration and the operating laser temperature. Thus, system  139  provides appropriate temperature compensation to ensure accurate pulse energy control, as discussed below regarding  FIGS. 56 and 57A-57B . 
       FIG. 56  illustrates an example algorithm  800  employed by motor/pulse control system  139  for controlling scanning system motor  120  and the pulsing of laser source  14 . It may be recognized that example algorithm  800  employs the usability control algorithm discussed above. 
     System  139  may initiate algorithm  800  once device  10  is in a ready state after passing initial start-up self-tests for verifying the appropriate functionality of various control elements. At steps  802  and  804 , system  139  waits for all four contact sensors  204   a - 204   d  to indicate contact with the skin and both displacement sensors  200   a  and  200   b  to indicate a displacement that meets the predetermined minimum displacement threshold (e.g., 1 mm). The predetermined displacement threshold may be defined by a predetermined number of identified surface features  74  of the skin, e.g., as discussed above regarding  FIGS. 38-46 . Both conditions must be satisfied before initiating a laser pulsing command. 
     When both conditions are met, the algorithm advances to step  806 , where main controller  144 A calculates (a) an appropriate scanning system motor speed and (b) an appropriate trigger delay time relative to a transition edge of each lenslet of the scanning element. The input for this calculation is the target laser pulse duration for a given desired pulse energy output. It is important for the motor speed and the laser trigger timing (as defined by the trigger delay time) to be properly synchronized in order for each laser pulse to be delivered within an optically usable portion of each respective lenslet of the rotating scanning optic. This process is discussed in greater detail below with respect to  FIGS. 57A and 57B . 
     After calculating the parameters at step  806 , system  139  begins pulsing laser  14  at step  808 , with each pulse being deflected by a different sector of the rotating scanning element  100  to provide an individual output beam  112  that is delivered to create a treatment spot on the skin. The laser pulses are executed with the appropriate scanning system motor speed and trigger delay time relative to a detected optical encoder signal, which is a square-wave pulse train generated by encoder sensor  203  monitoring an encoder wheel  121  rotated by motor  120 . Encoder wheel  121  may have a number of detectable features (e.g., slotted openings), each corresponding to one sector of multi-sector scanning element  100 , and each aligned with a transition edge of the corresponding sector (e.g., a transition edge between adjacent lenslets). Thus, system  139  can monitor the optical encoder signal generated by encoder sensor  203  to detect each detectable feature (e.g., slotted opening) rotating through a particular location, and thereby detect a transition edge of each sector of the rotating scanning element. 
     Accordingly, system  139  commands the generation of one laser pulse for each detected sector of scanning element  100  (based on the signal from encoder sensor  203 ). Throughout the laser pulsing, controller  144 A maintains a count of the total pulses delivered, as indicated at step  810 , and determines a completion of the treatment when the pulse count reaches a predetermined pulse count for the particular treatment session, as indicated at step  812 . Thus, the total energy dose delivered during the treatment session is independent of the glide speed of the device  10 . 
     During the treatment session, controllers  144 A and/or  144 B continually check for various safety fault conditions. For example, at step  814 , controller  144 A checks for a motor stall condition, which may be detected when the motor speed (e.g., as detected based on signals from encoder sensor  203 ) either (a) differs from the motor speed commanded at step  804  by more than a predetermined amount (e.g., ±20%) or (b) falls below a predetermined stall threshold (e.g., 240 rpm). Further, at step  816 , secondary controller  144 B may provide an independent check of various laser parameters (e.g., pulse duration, current, and voltage) to monitor for laser over-pulse-duration, laser over-current, or degraded laser (based on laser diode voltage), for example. If any of the fault conditions are detected at step  814  or  816 , the laser pulsing will stop immediately and the device will report an error condition on the display user interface, as indicated at  816 . The checks at steps  814  and/or  816  may be performed in any suitable frequency, e.g., after each pulse, after each scan of the input beam, or at a frequency unrelated to the pulse or scan frequencies (e.g., every 200 ms). 
     Assuming no fault condition at step  814  or  816 , the controller  144 A applies the usability control conditions for continuing the pulsing of laser  14  at step  820  and  822 , which conditions are less stringent than the conditions at steps  802  and  804  for allowing the initial pulse, e.g., as discussed above regarding the usability control algorithm of  FIG. 49 . In this example, valid inputs from only two of the four contact sensors  204   a - 204  (specifically, valid input from at least one of “bottom” contact sensors  204   a  and  200   b  and valid input from at least one of “top” contact sensors  204   c  and  200   d ), combined with valid input from only one of the two displacement sensors  200   a  and  200   b  are required for continued pulsing. Therefore, the laser pulsing will continue as long as any pair of contact sensors along the critical scan-beam edges indicate contact with the skin and either one of the two displacement sensors indicate the required displacement of device  10 . However, if the conditions at steps  820  and  822  are not met for a continuous period referred to as the “signal de-bouncing period” (e.g., one second), the conditions reset to the more stringent standard for allowing an initial pulse, as indicated as step  824  and the return to steps  802  and  804 . The different standards for initiating pulsing and for continuing pulsing once initiated may achieve both safety and usability for the gliding movement of the application end  42  of device  10  across the skin. That is, due to the expected treatment skin curvature and the bony structure underneath, it is often usually difficult to obtain perfect skin contact and displacement in a gliding treatment motion, except for during the initial contact and movement. 
     In the illustrated example algorithm  800 , system  139  also compensates for temperature variations of laser  14 , due to the fact that laser performance (e.g., output power or wavelength) typically varies with temperature. Thus, the temperature compensation provided by system  139  may ensure accurate control of the laser pulse energy (i.e., energy output per pulse). Laser diode optical output power varies with its operating temperature. This variation normally corresponds to about 1% power drop per degree C. of temperature rise. To maintain a constant laser pulse energy, either the laser drive current or the pulse duration can be varied. Because of the linear nature of the pulse energy relative to the pulse duration (e.g., as apposed to the generally non-linear relationship between current and pulse energy), adjusting the laser pulse duration may be the preferred option, particularly when the compensation range is not large, e.g., less than 25 degree C. temperature change. In this example implementation, the new laser power is recalculated in each control loop based on the actual measured temperature of heat sink  36 , as indicated at  826 . The resulting required laser pulse duration to achieve the set target pulse energy is then fed back as input for calculating the scanning system motor speed and trigger delay time at step  806 . The entire algorithm  800  working in real-time is designed to achieve closed-loop control of scanning system motor speed and laser pulsing parameters based on the dynamic operating temperature of laser  14 . 
       FIG. 57A  illustrates an example algorithm  830  corresponding to steps  804  and  806  of algorithm  800 , according to an example embodiment.  FIG. 57B  illustrates radiation pulse parameters with respect to a rotating beam-scanning element  100 , with reference to control algorithm  830  of  FIG. 56 , according to an example embodiment. 
     At step  832 , device  10  receives a user setting, e.g., a treatment level or a “comfort level” (discussed below in more detail) for a treatment session, via any suitable user interface  28 , e.g., a treatment level selection button or switch  220 . 
     At step  834 , motor/pulse control system  139  determines a target energy/MTZ corresponding to the selected treatment level or comfort level. As an example only, device  10  may allow the user to select between a low level treatment, a medium level treatment, and a high level treatment, which are programmed to deliver 5 mJ/MTZ, 10 mJ/MTZ, and 12 mJ/MTZ, respectively. 
     At step  836 , system  139  determines a current actual temperature of or related to the laser  14  (e.g., a temperature of laser package  250  or heat sink  36 ), e.g., from one or more temperature sensors  208 . 
     At step  838 , system  139  calculates a target pulse duration required to provide the target energy/MTZ determined at step  834 , and adjusts based on the temperature measured at step  836 , e.g., based on known temperature/performance relationships for the particular laser  14  of device  10  stored in memory  146 . Thus, system  139  calculates the target pulse duration based on the target energy/MTZ and the current temperature of related to laser  14 . 
     Based on the calculated pulse duration, system  139  calculates a target motor speed for scanning system motor  120  that will provide a pulse arc length on a deflection sector  140  of rotating scanning element  100  that matches a predetermined usable portion for that deflection sector  140 , at step  840 . The length and/or rotational location of the usable portion of each deflection sector  140  of element  100  may be the same, or may be different, e.g., depending on the physical geometry of element  100 . In some embodiments, a common usable portion may be predetermined and used for all sectors, to simplify the control process. 
       FIG. 57B  illustrates a representation of a scanning element  100  having multiple deflection sectors  104  (e.g., lenslets  104 ). In particular,  FIG. 57B  shows a usable portion, UP, for a particular deflection sector  104   1 . The remaining portions of the sector  104   1  may be unusable for generating the corresponding output beam  112  due to interference or other affects related to the transitions between sector  104   1  and its adjacent sectors  104 . In other embodiments, the entire width of each sector  104  may be usable. 
     Thus, at step  840  system  139  calculates the target motor speed based on the pulse duration calculated at step  838  that will provide a pulse arc length, PAL normal , on deflection sector  140  equal to the usable portion UP of that sector  140 . In some embodiments, device  10  may provide for an alternative operational mode (e.g., a “comfort” mode), in which the frequency of treatment spot/MTZ generation is reduced by reducing the motor speed, but maintaining the pulse delivery parameters of the normal mode operation. Thus,  FIG. 57B  also shows a pulse arc length, PAL comfort , that is delivered to sector  104   1  in an example “comfort mode” operation in which the motor speed of motor  120  is reduced by 50%, while maintaining the pulse parameters. 
     At step  842 , system  139  commands motor  120  to operate at the target motor speed. At step  844 , system  139  determines the actual speed of motor  120 , e.g., based on signals from an optical encoder sensor  203  that reads detectable features of encoder  121  as they pass by a particular point in space. In other embodiments, device  10  may utilize any other suitable type of motor speed sensor. 
     At step  846 , system  139  compares the actual motor speed determined at step  844  with the target motor speed calculated and commanded at steps  840  and  842  to determine a resulting motor speed offset, if any. If the motor speed offset is above a predetermined threshold, (e.g., zero, a predetermined percentage (e.g., 1%) of the target motor speed, a predetermined speed offset (e.g., 10 rpm), or any other suitable threshold), the algorithm loops back to step  836  to determine the current temperature and repeat steps  836 - 844  based on the current temperature. If the motor speed offset is below the predetermined threshold, system  139  may apply a feedback algorithm at step  848  to correct the motor speed, and the algorithm loops back to step  836 . 
     In this manner, system  139  executes a closed-loop algorithm for controlling the motor speed of motor  120  to compensate for temperature changes of laser  14  in real-time. 
     As shown in  FIG. 57A , in parallel with the command and control of the motor speed at steps  842 - 848 , system  139  commands laser  14  to generate pulses at steps  850 - 852 . In particular, at step  850 , system  139  calculates a pulse trigger delay time such that the delivered pulse (of the duration calculated at step  838 ) begins at the start of the usable portion UP of the respective sector  104 , as opposed to the transition point between sectors  104 . The arc through which sector  104   l  passes during the pulse trigger delay time is indicated in  FIG. 57B  as arc length AL delay . System  139  may calculate the pulse trigger delay time based on the motor speed calculated at step  840 , and with knowledge of arc length AL delay . 
     System  139  then pulses laser  14  at step  252  according to the pulse duration and pulse trigger delay time determined at steps  838  and  850 , wherein the pulse trigger delay time and pulse activation for each pulse is triggered based on the signal from encoder sensor  203 . For example, each detection of a detectable feature of encoder  121  (e.g., each corresponding to a transition point between adjacent sectors  104  of element  100 ) by encoder sensor  203  initiates the pulse trigger delay time, after which laser  14  is pulsed for the duration calculated at step  838 . Thus, in such embodiments, encoder  121  operates as the trigger for each pulse. 
     In some embodiments, each of the various steps of algorithm  830  may be repeated at any desired frequency, e.g., after each pulse, after each scan of the input beam, or at a frequency unrelated to the pulse or scan frequencies (e.g., every 50 ms). For example, in the illustrated example, the pulse trigger delay time is updated after each scan of the input beam (i.e., after each rotation of element  100 ). 
     By calculating a pulse duration that fills up the usable portion of each sector  104  as discussed above, system  139  may maximize the usable portions of element  100 , which may allow for an efficient use of laser  14  and scanning system  48  to provide the desired treatment. 
     Laser Control Circuits 
     In some embodiments, device  10  may include two (or more) independent laser current switch controls for safety redundancy, one connected to the laser anode side and the other to the cathode side. For example,  FIGS. 58 and 59  illustrate electrical schematics for two independent laser current switch controls of an example device  10 , including a first digital control circuit connected to the laser anode side ( FIG. 58 ) and a second dimmer-type control circuit connected to the cathode side ( FIG. 59 ). 
     With reference to  FIG. 58 , the anode side switch is a digital switch, referred to as the sentinel FET switch. The circuit switches the laser current completely on or off. This digital switch may be used to turn off the laser quickly whenever a safety related error condition is detected. In contrast, with reference to  FIG. 59 , the cathode side switch functions as a linear dimmer control, referred to as the control FET. This circuit can adjust the laser current from zero to any set value within the design range, and may be used to set the target laser power for compensating for any significant inherent variations among different laser diodes (e.g., based on manufacturing differences). The cathode side switch may also be used as a secondary safety switch to turn down the laser current to zero value when the sentinel switch on the anode side is off. 
     One simple yet stable circuit implementation of the constant pulse current control is shown in the schematics with two OpAmp stages. The first OpAmp IC1A may be a fixed gain preamp to boost the laser current sense signal flowing through the cathode side control FET. The second OpAmp IC1B may be a control stage acting as an integrator to match the laser current to the set-point established at the positive input side of the OpAmp, i.e., the voltage set by the potentiometer or any other means. The IC1B input voltage set-point may be used to adjust the laser current from zero to any desired value within the design range. For example, with an appropriate set of circuit component values, the laser pulse current can be adjusted from 0 to 6 A with a pulse rise and fall time less than 0.4 ms. These may be desirable or even ideal operating conditions for fractional treatment laser diode control, for certain embodiments of device  10 . 
     Prevention of Treatment Spot Overlap 
     As discussed above, in some embodiments, device  10  may be configured to prevent, limit, or reduce the incidence or likelihood of treatment spot overlap, e.g., based on feedback from one or more sensors  26  (e.g., a displacement sensor  200 , speed/motion sensor  202 , and/or a dwell sensor  216 ). For example, displacement-based control system  132  and/or usability control system  133  discussed above may operate to prevent, limit, or reduce the incidence or likelihood of treatment spot overlap. In addition or in the alternative to displacement-based control system  132  and/or usability control system  133 , device  10  may include further controls or features for preventing, limiting, or reducing the incidence or likelihood of treatment spot overlap. 
     For example, in some embodiments, the pulse rate may be automatically adjustable by device  10  and/or manually adjustable by the user, e.g., to accommodate different manual movement speeds and/or different comfort levels or pain tolerance levels of the user. 
     Some embodiments include other devices or techniques that individually or in combination provide over-treatment protection, e.g., to prevent pulse stacking, firing on the same area(s), an excessive treatment spot  70  density, or other non-desirable treatment conditions. For example, in some embodiments, device  10  ceases to operate (e.g., generate or deliver beams) when stationary condition of device  10  is detected. A stationary condition may be determined using one or more sensors, e.g., any one or more displacement sensors, motion sensors, speed sensors, dwell sensors, vibration and tilt sensors, and/or accelerometers. Such sensors may generate signals based on capacitance, optical reflection, remittance, scattering variation, acoustical reflection variation, acoustical impedance, galvanic potential, potential difference, dielectric constant variation, or any other parameter. 
     In some embodiments, device  10  uses local pyrometry (alone or in combination with other techniques mentioned above) to detect a stationary condition. The treatment area may be optically measured by local thermal imaging of the skin, and a stationary condition may be detected where local heating of the skin exceeds a threshold temperature or other parameter value. 
     In some embodiments, device  10  delivers an “encouragement beam” or a scanned row of encouragement beams when a stationary condition is detected. For example, a single beam or scanned row of beams at a non-damaging but higher than normal energy (e.g., causing discomfort but not damage) may be delivered if a stationary condition is detected, to encourage the user to move device  10 . 
     A stationary condition may further be measured by bulk heating measurement, for example. If the tip of the treatment delivery device or the sensed skin temperature or region of skin temperature begins to heat above a threshold, loss of motion is detected, or excessive treatment in the area is detected. 
     As another example, device  10  may deliver heat or cold to the skin to encourage motion, as dwelling in one location may become uncomfortable. As another example, mechanical rollers may be used to detect a non-motion condition. Alternatively, motorized rollers may drive motion of device  10  across the skin, thus physically avoiding a non-motion condition. 
     In some embodiments, physiological feedback based on beam characteristics may be exploited, e.g., by designing the output for treatment efficacy as well as perception of the presence of treatment. For example, discomfort may be exploited such that overtreatment is discouraged by pain feedback that increases with excessive treatment. 
     In some embodiments, photobleaching may be used with indigenous or exogenous substances. For example, the skin may be treated with a dye that is photobleached by the treatment beam or by a separate bleaching beam used to bleach the treated area and potentially its surrounding areas. In this example, device  10  may be configured to detect the presence of the unbleached dye and would allow treatment only on areas with unbleached dye, thus preventing repetitive scanning on the same areas (since that would be photobleached). 
     Example Embodiments of Device  10  for Providing Fractional Treatment 
     In some embodiments, device  10  is a fractional skin treatment device, which delivers scanned beams  114  to the skin, e.g., to treat wrinkles, pigmentation and coarse skin. Each delivered beam  114  creates a treatment spot  70  on the skin  40 , which produces a corresponding micro-thermal zone (MTZ), as discussed above. The device application end  42  may be manually glided across the skin  40  (in a gliding mode or a scanning mode, for example) any suitable number of times to create an array of treatment spots  70 . The skin&#39;s healing response in turn rejuvenates the skin. In some embodiments, device  10  may yield results similar to professional devices, but leverages a home daily use model to gradually deliver the equivalent of a single professional dose over multiple treatments or days (e.g., a 30 day treatment routine). 
       FIG. 60  shows a three-dimensional cross-section of a volume of skin for illustrating the process of a non-ablative fractional treatment consisting of an array of MTZs in the skin, with each MTZ corresponding to treatment spot  70  created by a delivered beam  114  from device  10 . Each MTZ is a small volume of denatured (or otherwise influenced, such as photochemical or photobiological) epidermis and dermis generally shaped as a column or elongated bowl and extending downward from the skin surface or subsurface in a direction substantially orthogonal to the skin surface. The damaged skin of the MTZ is surrounded by untreated (and thus not denatured, in this example) skin. Because of the proximity of healthy skin cells, the damaged skin of the MTZ heals relatively quickly (as compared to traditional non-fractional treatments, such as CO2 laser resurfacing) and reduces wrinkles, scarring, and/or uneven pigmentation as part of the healing process. During the healing process, MENDS (microscopic epidermal necrotic debris) may be formed. Since the MTZs typically cover only a fraction (e.g., less than 1% to about 70% of the skin surface, side effects may be substantially reduced as compared to traditional non-fractional treatments, such as CO2 laser resurfacing. In some home-use embodiments of this disclosure, coverage fraction may be between 0.25% and 5% of the skin per treatment. In some embodiments, device  10  is configured such that the size and shape (e.g., height and width and depth) of the MTZs spare many of the stem cells and melanocytes in the papillary dermis. 
       FIG. 61  illustrates an example hand-held device  10 A according to certain embodiments of the present disclosure. Device  10 A includes a device housing  24 , which houses a radiation source  14  and optics  16  (including a scanning system  48 ) for delivering scanned beams to the skin. Device  10 A includes a tip portion  42  configured to be placed in contact with the skin and glide across the skin during a treatment session. Tip portion  42  may include a window (e.g., window  44  discussed above) through which the scanned beams are delivered to the skin. 
     In addition, any number and type(s) of sensors  26  may be located on the tip portion  42 , e.g., as discussed above. For example, device  10 A may include a displacement sensor  200 , such as the single-pixel type displacement sensor  200 A,  200 B, or  200 C discussed above, or the mouse-type displacement sensor  200 D discussed above. In addition, one or more skin contact sensors  204  may be provided to detect the presence of a target in close proximity to the device application end  42 , prior to delivery of laser pulses. In some embodiments, the skin contact sensor(s)  204  may include pressure switches, capacitive touch sensors, or other sensor technologies. In certain embodiments, capacitive touch sensors are preferred as they may be less likely to be actuated by surfaces other then the user&#39;s skin. 
     In some embodiments, one or more roller devices are provided on the device application end  42 . Due to the scan line nature of treatment it may be preferred that device  10 A is glided in a glide direction that generally perpendicular to the scan direction (i.e., analogous to shaving with a liner cutting head, or a blade). Roller devices oriented on device application end  42  and configured to contact the skin may help guide the gliding of device  10 A in the desired glide direction. Also, roller devices may help device  10 A glide smoothly across the dry skin, both for user comfort and even application of laser pulses. In some embodiments, roller devices may reduce stiction between the device application end  42  and the skin. Roller devices may also provide a good visual indication of proper glide direction. 
     Device  10 A may be configured to provide any number of different treatment levels (e.g., low, medium, and high) or modes, which may be defined by one or more different parameters, such as, for example:
         Energy per beam  112 : by controlling radiation source  14 ,   Beam wavelength: e.g., by controlling the temperature of radiation source  14 , or by selectively controlling the activation of radiation sources or emitters configured for different wavelengths.   treatment spot array density: by controlling a minimum threshold distance used by displacement-based control system  132  for enabling delivery of output beams  112  (and thus generation of treatment spots), e.g., as discussed above regarding  FIGS. 38-46 . As discussed above, such minimum threshold distance may be expressed as a measured distance or as a number of identified surface features of the skin.   treatment spot size or shape: for example by adjusting the position of radiation source  14  and/or one or more optical elements.   One or more treatment session delimiters, such as discussed above with respect to  FIG. 47  (e.g., total number of treatment spots in a treatment session).   Radiation mode: e.g., any of the modes discussed above regarding  FIGS. 28-29 .   Beam scanning speed, e.g., by controlling the speed of scanning system motor  120 .       

     Further, in embodiments/operational modes in which radiation source  14  is pulsed:
         Pulse on time (i.e., pulse width): by controlling radiation source  14 ,   Pulse off time (i.e., pulse delay): by controlling radiation source  14 ,   Pulse frequency: by controlling radiation source  14 ,   Pulse wave profile (e.g., square wave, sine wave, etc.): by controlling radiation source  14 .       

     Each selectable treatment level or mode may be defined by combination of one or more of such parameters, or other parameters. In some embodiments, the selectable treatment levels or modes are predefined and stored in device  10  to accommodate a range of user preferences with respect to treatment sensation and pain, treatment time, or other aspect of a treatment. For example, device  10  may provide selectable treatment levels of low, medium, and high. The low level may be defined by a relatively low energy/pulse and relatively large minimum distance between scanned rows (e.g., as enforced by displacement-based control system  132 ), whereas the high level may be defined by a relatively high energy/pulse and relatively small minimum distance between scanned rows (e.g., as enforced by displacement-based control system  132 ). The low level may be suitable for pain sensitive users, while the high level may be suitable for more aggressive users. In other embodiments, individual parameters that define treatment levels or modes may be selectable or adjusted by a user, e.g., via a suitable user interface  28 . 
     The treatment levels or modes provided by device  10  may be selected in any suitable manner, e.g. automatically by control system  18  or by a user. Control system  18  may automatically select a treatment level or mode based on any suitable information, e.g., feedback from one or more sensors  26 , or according to a predefined multi-session treatment plan, or based on any other relevant information. Alternatively, control system  18  may automatically select a treatment level or mode based on selections made by a user, e.g., a selected body part to be treated, a selected treatment time, a selected energy level, etc. 
     Alternatively, the user may select the current treatment level or mode via any suitable user interface  28 , e.g., one or more buttons, switches, knobs, or a touch screen. For example, device  10 A includes a power/treatment control button  900  that allows selection between different treatment levels or modes, as well as turning device on/off. For example, button  900  may be a single momentary pushbutton control that powers on device  10  when pressed. Subsequent presses then cycle through different power settings. For example, pressing button  900  may progress through the following sequence of settings in order:
         [off]→[on: low]→[on: medium]→[on: high]→[off]
 
As another example, pressing button  900  may progress through the following sequence of settings in order:
   [off]→[on: last used treatment level]→[on: next treatment level] . . . →[on: next treatment level] with a long press required to turn the device back off.       

     Lighted setting indicators  902  may indicate the currently selected treatment level or mode, as selected using power/treatment control button  900 . In one embodiment, an array of three light emitting diodes (LEDs) indicates the on/off state and treatment level setting according to the following code:
         all three off=device off; one on=level 1 or low two on=level 2 or medium; all three on=level 3 or high       

     A lighted battery indicator  904  may indicate the charge status of a battery  20  provided in device  10 A. In some embodiments, indicator  904  is a multicolor LED for indicating battery status, e.g., a red/green LED indicator in which green indicates full/good charge, flashing green indicates need to recharge soon, and red indicates depleted battery/must recharge prior to using. 
     In some embodiments, device  10 A includes a tactile feedback device within housing  24  to provide tactile feedback to the user, e.g., vibration type feedback, to indicate various events (e.g., button presses, proper usage, the pausing of a treatment session due to particular sensor feedback, etc.). Such tactile feedback is indicated generally by reference number  906 . 
     Because device  10 A may likely be used in front of a mirror, and held in a variety of positions by different users, placement of visual indicators, such as LED&#39;s, in a manner that provide universal visibility can be difficult. Thus, device  10 A may include one or more “wide area” type indicators, such as light rings, glowing housings, or other wide area lighting device that are visible from a wide range of positions of the user and device  10 A. Alternatively, or in addition, the visual indicator(s) may be carefully placed to provide good viewing under many conditions, for example, visible lights around the treatment beam aperture that could be seen for example as a glow around the skin in both direct visualization, peripheral visualization such as when treating around the eyes, or in a mirror. 
     Device  10 A may include “proper usage” feedback in any suitable manner, to indicate to the user that they are using the device properly (e.g., using proper technique) and that the device is operating properly (e.g., proper laser output). For example, device  10  may provide audible “happy sounds,” LED indications, both discreet and wide area type indicators as described above, tactile feedback  906  (e.g., vibrations), and/or any other suitable feedback. Control system  18  may provide such feedback when all sensors  26  are satisfied and laser pulses are enabled. 
     Device  10 A may also provide pacing assistance and automatic shutoff functionality. A desired full face treatment may consist of a substantially uniform patter of treatment spots across a target area (e.g., the face). To facilitate uniform treatment of the target area, device  10 A may provide feedback to the user indicating when to move from one region of the target area to another, e.g., after a predetermined fraction of the total treatment spots for the session have been generated on the target area. For example, one embodiment provides 36 treatment spot/cm2, which corresponds to about 10,000 treatment spots for an average face of 300 cm2. The face may be considered as consisting of four quadrants. For a full face treatment of 10,000 treatment spots, 2,500 treatment spots should be generated in each quadrant to provide uniform treatment. Thus, device  10 A may provide feedback to the user to facilitate movement from one quadrant to the next, after 2,500 treatment spots have been generated, after 5,000 total treatment spots have been generated, and after 7,500 total treatment spots have been generated. The user may know (e.g., from a user manual or from instructions provided by device  10 A, e.g., via a display  32 ) to move from quadrant to quadrant upon each such feedback. The feedback may be audible, visual, and/or tactile feedback. Device  10 A may then automatically power down after delivering the full 10,000 treatment spots. 
     In some embodiments, device  10 A may require communication with a removable cartridge  910  or a separate item  912  in order to enable activation of device  10 A. For example, a bottle of topical solution may include an RFID tag  912  configured to communicate an ID to device  10 A in order to enable operation of device  10 A. As another example, device  10 A may require a specialized battery that has a limited lifetime, or the device may have a hardware cartridge that provides a preset number of treatments or minutes or other parameter. In still other examples, the device may require communication with an external system, like a PC monitor through visual signals on the PC monitor or the internet through TCP/IP or other protocols. Topical consumables, hardware consumables, or electronic keys like these may be configured to provide recurring revenue associated with device use. 
     In some embodiments, device  10 A may include devices for inductive coupling of the electrical charger  720  to handheld device  10 . This may be coupled in a receptacle/stand type arrangement  730 , or a pad or tray on which the hand piece lies for storage between treatments. Such configuration may help avoid the need to manually plug device  10  in for recharging on a frequent basis. With the inductive charging stand or pad, the features of a wall plug-in charger may be incorporated into the charging stand  730  and inductively provide A/C charging current to the device charge circuit. 
       FIGS. 62A and 62B  illustrate example configurations of particular components of device  10  according to certain embodiments. In particular,  FIGS. 62A and 62B  illustrate example arrangements of a radiation engine  12  similar to that shown in  FIG. 34 , an upstream optic  64 , a cup-shaped rotating scanning element  100 B, a battery  20 , and an application end  42  including a window  44 . 
       FIG. 63  illustrates another example configuration of particular components of device  10  according to certain embodiments. In particular,  FIG. 58  illustrate an example arrangement of a radiation engine  12  similar to that shown in  FIGS. 33A-33B , an upstream optic  64 , a cup-shaped rotating scanning element  100 B, and an optional downstream optic  64 ′ proximate an application end of the device. 
       FIGS. 64A-64D  illustrate various views of an example device  10  that utilizes a cup-shaped rotating scanning element  100 B, according to certain embodiments. In particular,  FIGS. 64A-64D  illustrate an example arrangement of a cup-shaped rotating scanning element  100 B, a radiation engine  12  similar to that shown in  FIG. 34 , an optional downstream optic  64 ′, a battery  20 , and an application end  42  that includes various sensors  200 ,  204 , and  214  disposed around optional downstream optic  64 ′. 
       FIGS. 65A-65D  illustrate various views of an example device  10  that utilizes a disc-shaped rotating scanning element  100 A, according to certain embodiments. In particular,  FIGS. 65A-65D  illustrate an example arrangement of a disc-shaped rotating scanning element  100 A, a radiation engine  12  similar to that shown in  FIG. 34 , an optional downstream optic  64 ′, a battery  20 , and an application end  42  that includes various sensors  200 ,  204 , and  214  disposed around optional downstream optic  64 ′. 
       FIGS. 66A-66B and 67A-67B  illustrate representations of the optical system  15  of example devices  10  shown in  FIGS. 64A-64D  and  FIGS. 65A-65D , according to various embodiments. In particular,  FIGS. 66A and 66B  illustrate the optical system  15  of example devices  10  shown in  FIGS. 64A-64D  and  FIGS. 65A-65D , according to embodiments in which optional downstream optic  64 ′ is omitted. In contrast,  FIGS. 67A and 67B  illustrate the optical system  15  of example devices  10  shown in  FIGS. 64A-64D  and  FIGS. 65A-65D , according to embodiments that include optional downstream optic  64 ′. 
     Referring to  FIGS. 66A and 66B ,  FIG. 66A  shows optical system  15  in the fast axis profile, while  FIG. 66B  shows optical system  15  in the slow axis profile, orthogonal to the fast axis profile. As shown, upstream optic  64  is a rod lens that influences (converges) the fast axis profile of the beam, but does not significantly influence the slow axis profile of the beam, while scanning element  100  (e.g., element  100 A or  100 B) influences (converges) the slow axis profile of the beam, but does not significantly influence the fast axis profile. In this example, each delivered beam  114  has a focal point or focal plane that is slightly above the surface of the skin  40 . In other embodiments, the focal point or focal plane of each delivered beam  114  may be co-planar with the surface of the skin  40 , or alternatively may be below the surface of the skin  40 . 
     Referring now to  FIGS. 67A and 67B ,  FIG. 67A  shows optical system  15  in the fast axis profile, while  FIG. 67B  shows optical system  15  in the slow axis profile. As shown, upstream optic  64  is a rod lens that influences (slightly converges or collimates) the fast axis profile of the beam, but does not significantly influence the slow axis profile of the beam; scanning element  100  (e.g., element  100 A or  100 B) influences (converges) the slow axis profile of the beam, but does not significantly influence the fast axis profile; and downstream optic  64 ′ is a second rod lens that further converges the fast axis profile of the beam, but does not significantly influence the slow axis profile of the beam. As with the example discussed above, each delivered beam  114  has a focal point or focal plane that is slightly above the surface of the skin  40 . In other embodiments, the focal point or focal plane of each delivered beam  114  may be co-planar with the surface of the skin  40 , or alternatively may be below the surface of the skin  40 . 
     In some embodiments, downstream optic  64 ′ provides a divergence of beam  114  of at least 50 mrad. In particular embodiments, downstream optic  64 ′ provides a divergence of beam  114  of at least 75 mrad. In specific embodiments, downstream optic  64 ′ provides a divergence of beam  114  of at least 100 mrad. For example, downstream optic  64 ′ may comprise a rod lens that provides a divergence of beam  114  of about 100 mrad. Such divergence may provide various level of inherent eye safety, with eye safety increasing with increased beam divergence. 
       FIGS. 68A-68C  illustrate various views of an example device  10  that utilizes a cup-shaped rotating scanning element  100 B, according to certain embodiments. In particular,  FIG. 68A  illustrates an example arrangement of internal components of device  10 , including a battery  20 , a fan  34 , and a radiation generation and delivery system including a radiation engine  12 , an upstream optic  64 , a cup-shaped rotating scanning element  100 B, a turning mirror  65 , and an optional downstream optic  64 ′ proximate an application end  42  of the device.  FIG. 68B  is a zoomed-in view of  FIG. 68A , showing the optics system  15  and general beam propagation directions. Finally,  FIG. 68C  shows the assembled device  10 , with the assembly shown in  FIG. 68A  being contained with an outer housing  24 , and showing beams  114  being delivered from the application end  42  of the device. 
     As shown in  FIG. 68B , radiation engine  12  includes a laser package  250  mounted to a heat sink  36 , and including a diode laser  14 . Radiation engine  12  may be configured similar to any of the arrangements shown in  FIG. 33A-33B ,  FIG. 34 , or  FIG. 35A-35B , or in any other suitable manner. As shown, optical system  15  includes (a) an upstream fast axis rod lens  64 , (b) a cup-shaped multi-sector rotating scanning element  100 B driven by a motor  120  and having a rotational axis arranged at a non-zero, non-90 degree angle with respect to the propagation direction of input beam  110  (e.g., as discussed above with respect to  FIG. 11A ); (c) a downstream planar turning mirror  65  configured to redirect, or “turn,” the array of output beams  112  output by rotating scanning element  100 B; and (d) an optional downstream fast axis rod lens  64 ′. 
     An encoder  121 , e.g., in the form of a wheel or disk, may be fixed to rotating scanning element  100 B such that the rotation of encoder wheel  121  remains synchronized with element  100 B. Encoder wheel  121  may be used for detecting or monitoring the rotation and/or rotational position of scanning element  100 B, which information may be used by control system  18  for various functions. Thus, encoder  121  may include a number of detectable features around a circumference or perimeter of encoder  121 . The number of detectable features may be equal to or a multiple of the number of sectors of scanning element  100 B, and may be fixed in a desired rotationally alignment relative to such sectors. Thus, information regarding the rotation and/or rotational position of scanning element  100 B may be determined or monitored by detecting the detectable features of encoder  121 . 
     For example, as discussed above regarding  FIGS. 56-57 , encoder wheel  121  may be used for triggering each beam pulse from radiation source  14 . For instance, in an embodiment in which encoder  121  includes one detectable feature corresponding to each sector of scanning element  100 B, the detection of each detectable feature passing by a particular point may be used to trigger a pulse from radiation engine  14  to be delivered through the sector of scanning element  100 B corresponding to that detectable feature. Each pulse may be triggered instantaneously upon detection of the next detectable feature as encoder  121  rotates, or may be triggered after some predetermined or dynamically determined delay time after the detection of the next detectable feature, e.g., as discussed above regarding  FIGS. 56-57 . Encoder  121  may also be monitored for safety features of device  10 , e.g., to instantaneously turn off radiation source  14  if it is determined that scanning element  100 B has stopped rotating. 
     Turning mirror  65  may be provided to redirect, or “turn,” the array of output beams  112  in order to provide a desired size, shape, or form factor of device  10 , e.g., to reduce the size of device  10  and/or to provide an ergonomic hand-held shape. With reference to  FIG. 68C , example device  10  includes an elongated handle portion  24 A configured to be gripped by a hand, a head portion  24 B, and an optical system  15  configured to deliver beams  114  in a direction generally perpendicular to the elongated direction of handle portion  24 A. Further, as shown in  FIG. 68C , the scan direction extends generally parallel to the elongated direction of handle portion  24 A. This configuration may be more comfortable or ergonomic for a user while operating device  10 , e.g., as compared to a configuration in which the beams are delivered in same direction as the elongated direction of handle portion  24 A, e.g., out of the end of device at which user interfaces  952 - 962  are located. 
       FIGS. 69A-69B and 70A-70B  illustrate representations of the optical system  15  of example device  10  shown in  FIGS. 68A-68C , according to certain embodiments. In particular,  FIGS. 69A and 69B  illustrate the optical system  15  of device  10  shown in  FIGS. 68A-68C , according to embodiments in which optional downstream optic  64 ′ is omitted. In contrast,  FIGS. 70A and 70B  illustrate the optical system  15  of device  10  shown in  FIGS. 68A-68C , according to embodiments that include optional downstream optic  64 ′. 
     Referring to  FIGS. 69A and 69B ,  FIG. 69A  shows optical system  15  in the fast axis profile, while  FIG. 69B  shows optical system  15  in the slow axis profile, orthogonal to the fast axis profile. As shown, upstream optic  64  is a rod lens that influences (converges) the fast axis profile of the beam, but does not significantly influence the slow axis profile of the beam, while scanning element  100  (e.g., element  100 A or  100 B) influences (converges) the slow axis profile of the beam, but does not significantly influence the fast axis profile. Turning mirror  65  may be a planar mirror that redirects but does not otherwise influence the output beams  112 . In this example, each delivered beam  114  has a focal point or focal plane that is slightly above the surface of the skin  40 . In other embodiments, the focal point or focal plane of each delivered beam  114  may be co-planar with the surface of the skin  40 , or alternatively may be below the surface of the skin  40 . 
     Referring now to  FIGS. 70A and 70B ,  FIG. 70A  shows optical system  15  in the fast axis profile, while  FIG. 70B  shows optical system  15  in the slow axis profile. As shown, upstream optic  64  is a rod lens that influences (slightly converges or collimates) the fast axis profile of the beam, but does not significantly influence the slow axis profile of the beam; scanning element  100  (e.g., element  100 A or  100 B) influences (converges) the slow axis profile of the beam, but does not significantly influence the fast axis profile; and downstream optic  64 ′ is a second rod lens that further converges the fast axis profile of the beam, but does not significantly influence the slow axis profile of the beam. Again, turning mirror  65  may be a planar mirror that redirects but does not otherwise influence the output beams  112 . As with the example discussed above, each delivered beam  114  has a focal point or focal plane that is slightly above the surface of the skin  40 . In other embodiments, the focal point or focal plane of each delivered beam  114  may be co-planar with the surface of the skin  40 , or alternatively may be below the surface of the skin  40 . 
     Returning to  FIG. 68C , device  10  may include various user interface features  28  at any suitable locations on device  10 . In this embodiment, device  10  includes user interface features  950 - 962 , including a use indicator  950 , a power/mode selector  952 , a selected mode indicator  954 , a treatment completion indicator  956 , a battery charge indicator  958 , an alarm indicator  960 , and a device lock indicator  962 . 
     Use indicator  950  may comprise any indicator (e.g., an LED) that indicates when device  10  is delivering radiation from application end  42 . Use indicator  950  may be positioned on device  10  at a location that is likely to be viewable by the user during a treatment. 
     Power/mode selector  952  may be any suitable interface (e.g., a depressible button, movable switch, capacitive switch, touch screen, etc.) used to turn device  10  on and off, and to select a operational mode of device  10  (e.g., a particular treatment mode, power level, “comfort level,” etc.) for a treatment session. For example, selector  952  may be a single momentary pushbutton control that powers on device  10  when pressed. Subsequent presses then cycle through different treatment levels. For example, pressing button  900  may progress through the following sequence of settings in order:
         [off]→[on: Level 1 operational mode]→[on: Level 3 operational mode]→[on: hi Level 3 operational mode]→[off]       

     Selected mode indicator  954  may indicate the currently selected treatment operational mode of device  10  (e.g., a particular treatment mode, power level, “comfort level,” etc.), as selected using power/mode selector  952 . In one embodiment, selected mode indicator  954  includes three LEDs, each corresponding to one of three different operational modes of device  10 , such that the currently selected operational mode can be indicated, e.g., by lighting the corresponding LED, or according to the following code:
         all three LEDs off=device off; one LED lighted=Level 1 operational mode; two LEDs lighted on=Level 2 operational mode; all three LEDs lighted=Level 3 operational mode       

     Treatment completion indicator  956  comprise any suitable interface for indicating an the successful completion of a particular recommended treatment session, e.g., which may be defined based on one or more treatment session delimiters, as discussed above. 
     Battery charge indicator  958  may indicate the charge status of a battery  20  provided in device  10 . For example, indicator  958  may be a multicolor LED for indicating battery status, e.g., a red/green LED indicator in which green indicates full/good charge, flashing green indicates need to recharge soon, and red indicates depleted battery/must recharge prior to using. As another example, indicator  958  may indicate the fraction of remaining charge of battery  20  by lighting a corresponding fraction of a battery icon. 
     Alarm indicator  960  may comprise any suitable interface for indicating an error condition regarding device  10 , e.g., an error condition identified by any control system  18  or electronics  30 . For example, alarm indicator  960  may comprise a multicolor LED configured to display different colors corresponding to different error conditions. In some embodiments, device  10  may also provide audible feedback to indicate the error condition. 
     Device lock indicator  962  may comprise any suitable interface for indicating whether device  10  is locked from operation (e.g., a child lock safety feature). In some embodiments, device  10  may be locked and/or unlocked by predetermined user interactions with one or more user interface  28 . For example, device  10  may be locked and/or unlocked by pressing a predetermined combination of buttons. As another example, device  10  may be locked and/or unlocked by holding one or more predetermined buttons by a predetermined time period, which time period may be indicated by visual, audible, or tactile feedback. For instance, in one embodiment, device  10  is locked and unlocked in the following manner. When the user presses and holds power/mode button  952 , the device  10  begins emitting a series of audible tones, one each second. The device can be locked by releasing button  952  after the fourth tone, but before the fifth tone. In response, device lock indicator  962  is illuminated and the operation and use of device  10 , including user interfaces  28 , are locked until device  10  is unlocked. Device  10  can be unlocked in the same way that the device is locked, by pressing and holding power/mode button  952  and then releasing after a period of between 4 and 5 seconds. 
     In addition to the above, device  10  may provide additional visual, audible, and/or tactile feedback regarding the status, settings, and/or operation of device  10 . For example, in embodiments in which scanning system motor  120  is turned on and off corresponding to on/off periods of treatment, the rotation of the motor  120  may provide an inherent tactile feedback (e.g., a slight vibration) indicating to the user that the device is operating. As another example, device  10  may be programmed to provide visual, audible, and/or tactile feedback at the completion of a treatment session, as well as at the completion of predetermined portions of the treatment session. For instance, device  10  may emit a tone after each 25% of a treatment session (e.g., indicating 25% completion, 50% completion, 75% completion, and 100% completion). Thus, for a full-face treatment, for example, the user may treat one quadrant of the face during each 25% of the treatment session. As discussed above, the treatment session may be defined by a predetermined treatment session delimiter, e.g., total number of beams  114  delivered, total number of scans, total energy delivered, etc. Thus, the predetermined portions (e.g., 25%) of the treatment may be defined based on such treatment session delimiter. For example, for a full-face treatment defined by delimiter of 20,000 total MTZs, device  10  may emit a tone after each 5,000 delivered beams  114 . 
     Operation Modes/“Comfort Levels” 
     As discussed above, device  10  may be configured to operate according to multiple different operational modes, which may be manually selectable by the user and/or automatically selectable by control system  18  of device  10 . Operational modes may include, for example, treatment modes (e.g., gliding mode vs. stamping mode), power levels (e.g., low delivered energy/MTZ, medium delivered energy/MTZ, or high delivered energy/MTZ), “comfort levels” (e.g., comfort level 1, comfort level 2, comfort level 3, etc.). Device  10  may be configured for any suitable number of selectable treatment modes, e.g., two, three, four, five, or more selectable treatment modes. 
     In one example embodiment, device  10  is configured for providing three selectable treatment levels, according to Table 2 below. 
                                     TABLE 2                       Level 1   Level 2   Level 3                                                    Raw laser power (i.e.,   3 W   3 W   3 W       emitted) (approximate)       Pulse duration (approximate)   3 ms   6 ms   7 ms       Total optical efficiency of   55%   55%   55%       device (approximate)       Energy per delivered beam   5 mJ   10 mJ   12 mJ       114/MTZ (approximate)       Treatment spot size,   0.06 mm 2     0.06 mm 2     0.06 mm 2         assuming no smearing       (approximate)       Treatment spot size,   0.10 mm 2     0.13 mm 2     0.14 mm 2         including smearing effects at       typical manual glide speed of       4 cm/sec (approximate)       Energy density at each MTZ,   5 J/cm 2     8 J/cm 2     9 J/cm 2         assuming typical manual       glide speed of 4 cm/sec       (approximate)       MTZ depth (approximate)   100 μm   250 μm   300 μm       Minimum displacement of   1 mm   1 mm   1 mm       device 10 between   (or n identified skin   (or n = 2 or 3   (or n = 2 or 3       consecutive scanned rows of   features, where n =   skin features)   skin features)       MTZs   2 or 3, for example)       scanning frequency   110 MTZ/sec   110 MTZ/sec   90 MTZ/sec       (assuming uninterrupted   (comfort mode,       scanning)   e.g., achieved by           reducing speed of           motor 120 by 50%)       Total MTZs for full-face   10,800 MTZ   21,600 MTZ   39,000 MTZ       treatment (300 cm 2 ) (e.g.,       enforced as a treatment       session delimiter)       Treatment spot density   36 MTZ/cm 2     72 MTZ/cm 2     130 MTZ/cm 2         (approximate)       Treatment time for full-face   2 min   5 min   10 min       treatment (approximate)                    
Focal Plane of Delivered Beams
 
       FIG. 71  illustrates a graph and cross-sectional representation of the fast axis and slow axis beam profile of a delivered beam  114 , illustrating the focal plane (FP) with respect to the surface of the skin  40 , according to certain example embodiment. For example,  FIG. 71  may correspond to embodiments of device  10  that use a laser diode as radiation source  14 , and include a downstream fast axis optic (e.g., rod lens)  64 ′, such as the embodiment shown in  FIGS. 68A-68C , for example. 
     The top portion of  FIG. 71  illustrates a graph of the beam diameter in both the fast axis and slow axis, as a function of distance beyond (downstream of) fast axis optic  64 ′. The bottom portion of  FIG. 71  shows a cross-sectional representation of the application end  42  of device  10 , including an outer surface  242  of application end  42 , fast axis optic  64 ′, and an open recessed area  244  through which beam  114  is delivered to the skin  40 . When application end  42  is pressed against the skin, a portion  40 A of the skin may press into the open recessed area  244 , as illustrated. The bottom portion of  FIG. 71  also identified various parallel planes A-E, wherein plane A is the plane of the apex of optic  64 ′, plane B is the plane corresponding to the minimum width, or waist, of the fast axis profile of beam  114 . plane C is the plane corresponding to the minimum width, or waist, of the slow axis profile of beam  114 , plane D is the plane corresponding to the maximum penetration of skin portion  40 A within the open recessed area  244  of the application end  42  of device  10 , and plane E is the plane corresponding to the outer surface  242  of the application end  42 . 
     In the illustrated example, optical system  15  of device  10 , including downstream fast axis optic  64 ′, scanning element  62 , and any other optical elements  16  of optical system  15 , are configured to converge the output beam in the fast and slow axes, respectively, such that each delivered beam  114  has a focal point or focal plane FP located slightly above the surface of the skin (i.e., outside the skin). As discussed above, the “focal point” or “focal plane” of each delivered beam is defined as the plane perpendicular to the propagation axis of the beam having the minimum cross-sectional area. In this embodiment, the focal plane FP lies between the waist of the fast axis beam profile (plane B) and the waist of the slow axis beam profile (plane C). 
     Thus, in this embodiment, beam  114  is slight diverging upon incidence with the skin, and creates a treatment spot of about 200-250 μm (in the fast axis direction) by about 200-250 μm (in the slow fast axis direction), which may be suitable, e.g., for a fractional treatment. In other embodiments, device  10  may be configured to provide any other suitable treatment spot sizes and/or other treatment spot shapes, e.g., by varying the details of the fast axis optics, slow axis optics, distances between optical elements, power of optical elements, etc. 
     Further, in other embodiments, device  10  may be configured such that the focal plane FP of delivered beams  114  is at the surface of the skin  40 , or below the surface of the skin  40  by any suitable distance, e.g., as suitable for various types of dermatological treatments.