Patent Publication Number: US-2022212026-A1

Title: Dermatological laser systems and methods with pressure sensing handpiece

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of and claims the benefit of priority to U.S. patent application Ser. No. 17/120,237, filed Dec. 13, 2020, entitled “Dermatological Systems and Methods With Handpiece for Coaxial Pulse Delivery and Temperature Sensing,” which is a continuation-in-part of Ser. No. 16/805,761, filed Feb. 29, 2020, now U.S. Pat. No. 10,864,380 B1, entitled “Systems and Methods for Controlling Therapeutic Laser Pulse Duration,” which is incorporated by reference herein in its entirety. This application claims the benefit of priority to both applications, which are hereby incorporated by reference herein in their entirety. This application also claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 63/125,354, filed Dec. 14, 2020, entitled “Dermatological Laser Systems and Methods With Pressure Sensing Handpiece,” which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to laser-based medical treatment systems, and more specifically to handpieces for controlling the temperature of a target skin area in the treatment of dermatological conditions. 
     A variety of dermatological conditions are treatable using electromagnetic radiation (EMR). Lasers are frequently used as an EMR source to treat a range of conditions including acne vulgaris, abnormal pigmentation, vascular skin conditions (e.g., spider veins), wrinkles and fine lines, dyschromia, and many others. Both pulsed and continuous-wave (CW) laser systems have been used. 
     Many dermatological EMR systems use a laser to photo-thermally damage a target tissue while preserving surrounding or adjacent non-targeted tissues or structures. The principle of selective photothermolysis, which involves thermally damaging a target tissue to promote a healing response, has led to the development of a variety of laser applications as standard of care in many medical fields including dermatology. 
     Damage to a target tissue during photothermolysis involves raising the temperature of the target tissue to a damage threshold temperature for a specified time period. For a desired level of thermal damage, there is a tradeoff between the temperature the target tissue must reach and the time that the temperature must be maintained. The same thermal damage may be achieved using a lower temperature if the time of heating is increased; if a higher temperature is used, a shorter heating time can achieve an equivalent thermal damage. To avoid thermal damage to non-targeted tissue, it is desirable to limit the heating time to the thermal relaxation time (TRT) of the target tissue, which is the time required for the target to dissipate about 63% of the thermal energy received from the laser pulse. TRT is related to the size of the target chromophore, and may range from a few nanoseconds for small chromophores such as tattoo ink particles, to hundreds of milliseconds for large chromophores such as leg venules. The TRT for a target tissue may be used for a particular laser system to select appropriate damage threshold temperatures for a desired level of thermal damage. For example, depending upon factors such as the laser power, fluence, spot size, etc. used in a given system, a damage threshold temperature to achieve a desired level of photothermolysis at time periods approximately equal to (e.g., slightly longer or shorter than) the TRT may be selected, minimizing damage to non-target tissues. 
     Photothermolysis can be achieved when three conditions are met: 1) the wavelength of the laser is chosen to have a preferential absorption in the target tissue over non-target tissue; 2) the laser pulse duration should be equal to or less than (=&lt;) the TRT of the target tissue; and 3) the laser fluence (i.e., energy per unit area) must be sufficient to exceed the thermal damage threshold of the target tissue. Together, these principles permit laser systems to be developed that deliver energy at specific wavelengths, pulse durations, and fluences to provide controlled energy to damage target tissue while leaving non-targeted surrounding tissues and structures substantially unaffected. 
     Selectivity as well as overall safety would be improved if the temperature of the skin could be dynamically controlled. In particular, most laser-based dermatological treatment systems do not provide reliable control of the temperature of the skin during treatment, since pulse durations and the number of pulses applied to a target treatment area are typically user-selected and maintained for a given treatment session until manually changed by the user (e.g., a laser technician, physician, nurse, etc.). There is a need for laser-based treatment systems providing better control of the skin temperature. Some embodiments of the present invention achieve this by using a handpiece capable of cooling the skin surface and/or measuring the actual skin temperature to dynamically control the temperature during a treatment. 
     Ideally, thermal damage is highly localized to only the particular target tissue (e.g., a particular skin layer at a particular location, or particular structures such as chromophores within a skin layer at a particular location), with nearby non-targeted tissues/structures remaining unaffected and available to facilitate the healing response in the targeted tissue. However, the structural complexity of the skin, which includes a variety of layers each having unique structural and functional characteristics, has limited the development of effective EMR-based treatments for many skin conditions. 
     Effectively reaching and limiting thermal damage to target structures within skin tissue by laser radiation is complicated by a variety of intrinsic and extrinsic factors. Intrinsic factors include, without limitation, the depth of the target structure within tissue and the associated absorption of light by non-targeted structures overlying the target (which may involve a plurality of intervening structures each having different light absorption and thermal characteristics), the scattering of light within the skin above the target, the TRT of the target structure and intervening non-target structures, and the removal (or non-removal) of heat by blood flowing through dermal and subdermal layers. Extrinsic factors include, also without limitation, the wavelength, pulse width, power, fluence, spot size, and other characteristics of the laser used to treat the target tissue or structure. 
     Acne vulgaris, more commonly referred to simply as acne, is the most common reason for office visits to dermatologists in the United States. Over 60 million Americans suffer from acne. Treatment options include topical applications such as disinfectants (e.g., benzoyl peroxide), retinoids (e.g., Retin-A), and antibiotics (e.g., clindamycin and erythromycin), as well as ingested compounds such as antibiotics (e.g., tetracycline), hormonal treatments (e.g., birth control pills), isotretinoin (Accutane, which has significant side effects), and optical treatments such as lasers. Laser treatments have the benefit of avoiding the side effects and inconvenience of pharmaceuticals and topical treatments but, at present, have limited effectiveness for reasons including the previously noted complexity of skin tissue structures and limitations of existing laser systems. More recently, nanosphere particles have been deposited into skin pores and/or follicles, followed by heating of the nanoparticles with laser light to treat acne. Photodynamic therapies, in which an agent is applied to the skin to increase its sensitivity to light, have also been used in conjunction with laser or other light (e.g., blue light) to treat acne. 
     There is a need for improved laser systems having greater efficacy for treating acne. 
     Precise temperature control of the target skin area becomes highly important when the patient&#39;s skin varies in thickness or composition, such that target skin areas (e.g., spots to which one or more laser pulses are applied) may reach significantly different temperatures when the same laser pulse is applied to different skin areas. The disparity in skin temperatures for a pre-defined laser pulse applied to different skin areas is magnified when a target structure (e.g., a sebaceous gland or sebum) is deeper in the skin, because of the greater scattering and absorption of energy by overlying tissue that occurs at greater skin depths. 
     Heating in tissues depends upon both the absorption of the irradiated tissue structures for the wavelength of laser light used, as well as their thermal relaxation times, which is a measure of how rapidly the affected structure returns to its original temperature. By delivering the laser energy in a pulse with a time duration less than the TRT of the target tissue, highly localized heating (and destruction) of a tissue target structure (e.g., melanin, sebum, sebaceous gland, collagen) can be achieved, minimizing damage to non-target structures (e.g., non-targeted skin layers, blood vessels, etc.). If the laser pulse duration is less than the TRT of the target tissue, no significant heat can escape into non-target structures, and damage to non-target structures is limited. 
     For deeper target structures such as sebaceous glands, which often range from 0.3-2.0 mm (more commonly 0.5-1.0 mm) below the outer surface of the epidermis, damage to overlying tissue structures is difficult to control or limit, since the laser energy must pass through overlying structures before reaching target structures. The overlying structures absorb energy depending upon their respective depths and absorption coefficients, and undesired damage may frequently occur. In some instances, the target structures are either sufficiently shallow, or the treatment temperature to which the target structures are raised is sufficiently low, that the heating of overlying structures may not cause excessive damage. Even where the risk of overheating the overlying structures of a relatively deep target is minimal, however, accurate temperature control of the target structure may be poor, resulting in overheating or underheating or the target structure, discomfort to the patient, or a combination of such undesired effects. 
     The skin surface may be cooled to limit the temperature increase (and damage) to non-target overlying structures, and to limit patient discomfort or pain. However, existing systems lack precise control of the cooling process. Achieving both a desired level of photothermal damage to deeper target structures and minimizing damage to non-target overlying structures has proven elusive. In many cases, the skin is cooled either too much—in which case the deeper target structure fails to reach a temperature damage threshold—or too little, in which case non-target overlying structures are damaged and the deeper target structure may be excessively damaged. There is a need for laser-based treatment systems having improved control of the cooling process to ensure that target structures reach a desired temperature (e.g., a thermal damage temperature) and that thermal damage to non-target structures is minimized or controlled to an acceptable level. There is a need for dermatological laser systems that are able to efficiently treat a variety of medical conditions to achieve these goals. 
     SUMMARY 
     In one embodiment, the invention comprises a system for treating the skin of a patient with a therapeutic laser pulse, the system comprising: a) a laser source for generating therapeutic laser pulses for application to a target skin area; b) a handpiece comprising: 1) a handpiece body optically coupled to the laser source and having a pulse delivery region adapted to deliver the therapeutic laser pulses to the target skin area through a pulse delivery aperture; 2) a contact sensing unit for contacting the skin of the patient, comprising: A) a frame surrounding at least a portion of the pulse delivery aperture; B) a plurality of contact sensing elements coupled to the frame at different locations, each contact sensing element sensing at least one of a force and a pressure at one of the different locations when the contact sensing unit is placed in contact with the skin; and c) a contact indicator for providing at least one of a force feedback parameter and a pressure feedback parameter to a system user based on the at least one of an applied force and an applied pressure sensed by the plurality of contact sensing elements. 
     In one embodiment, the invention comprises a system for treating the skin of a patient with a therapeutic laser pulse, the system comprising: a) a laser source for generating therapeutic laser pulses for application to a target skin area; b) a handpiece comprising: 1) a handpiece body having a first region optically coupled to the laser source and a second region adapted to deliver the therapeutic laser pulses to the target skin area; 2) a contact cooling unit located at the second region of the handpiece body, the contact cooling unit comprising a contact cooling window having A) a contact surface adapted to contact and cool a first skin area comprising the target skin area, and B) a periphery; and 3) a contact sensing unit for contacting the skin of the patient, comprising: A) a frame surrounding at least a portion of the contact cooling window periphery; B) a first contact sensing element at a first location on the frame to sense at least one of an applied force and an applied pressure at the first location when the contact sensing unit is placed in contact with the skin; C) at least a second contact sensing element at a second location on the frame to sense at least one of an applied force and an applied pressure at the second location when the contact sensing unit is placed in contact with the skin; and c) a contact indicator for providing at least one of a force feedback parameter and a pressure feedback parameter to a system user based on the at least one of an applied force and an applied pressure sensed by the first contact sensing element and the at least a second contact sensing element. 
     In one embodiment, the invention comprises a system for treating the skin of a patient with a therapeutic laser pulse, the system comprising: a) a laser source for generating therapeutic laser pulses for application to a target skin area; b) a handpiece comprising: 1) a handpiece body optically coupled to the laser source and having a pulse delivery region adapted to deliver the therapeutic laser pulses to the target skin area through a pulse delivery aperture; 2) a skin temperature sensing unit comprising: A) at least one temperature sensing element selected from an electrical sensing element and an infrared energy sensing element, the at least one temperature sensing element generating a temperature signal indicative of the surface temperature of the target skin area; and B) a processor for determining the surface temperature of the target skin area at a desired skin temperature determination rate based on the temperature signal; 3) a contact sensing unit for contacting the skin of the patient, comprising: A) a support frame surrounding at least a portion of the pulse delivery aperture; B) a plurality of contact sensing elements coupled to the support frame at different locations, each contact sensing element sensing at least one of a force and a pressure at one of the different locations when the contact sensing unit is placed in contact with the skin; and c) a contact indicator for providing at least one of a force feedback parameter and a pressure feedback parameter to a system user based on the at least one of a force and a pressure sensed by the plurality of contact sensing elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional illustration of skin tissue depicting the epidermis, dermis, and hypodermis, with a laser pulse applied to a portion thereof. 
         FIG. 2  is a cross-sectional illustration of skin tissue depicting a hair follicle and a sebaceous gland. 
         FIGS. 3A and 3B  are graphs illustrating the absorption coefficients of human sebum lipid, water, and melanosomes for various wavelengths of light. 
         FIG. 4A  is a graph illustrating a surface temperature profile of a target skin area according to a mathematical model of a treatment with a laser pulse. 
         FIG. 4B  is a graph illustrating a sebaceous gland temperature profile within a target skin area according to the mathematical model of the laser pulse of  FIG. 4A . 
         FIG. 5A  is a graph illustrating a surface temperature profile of a target skin area before, during, and after a laser pulse treatment with skin cooling, according to a mathematical model. 
         FIG. 5B  is a graph illustrating a sebaceous gland temperature profile within a target skin area before, during, and after a laser pulse treatment with skin cooling, according to the mathematical model of  FIG. 5A . 
         FIG. 5C  is more detailed graph illustrating a surface temperature profile for a target skin area during treatment with a laser pulse according to the mathematical model of  FIG. 5A . 
         FIGS. 6A and 6B  are block diagrams of embodiments of a dermatological treatment system according to the present invention. 
         FIGS. 7 and 8  are simplified figures of a handpiece according to an embodiment of the present invention. 
         FIGS. 9A and 9B  are perspective views of a handpiece according to an embodiment of the present invention. 
         FIGS. 9C, 9E, and 9G  are partially exploded views of the handpiece of  FIGS. 9A and 9B . 
         FIGS. 9D and 9E  are optical schematics showing optical paths in the handpiece of  FIGS. 9A and 9B . 
         FIG. 10  is a flowchart illustrating a treatment method according to one embodiment of the present invention. 
         FIG. 11A  is a perspective view of a handpiece according to an embodiment of the present invention. 
         FIG. 11B  is a partially exploded view of the handpiece of  FIG. 11A . 
         FIG. 11C  illustrates an embodiment of a flexcircuit use in an embodiment of the handpiece of  FIG. 11A . 
         FIG. 11D  is a cross-section of view along section line  11 D of  FIG. 11A . 
         FIG. 12A  is a perspective view of a handpiece according to an embodiment of the present invention. 
         FIG. 12B  is a partially exploded view of the handpiece of  FIG. 12A . 
     
    
    
     DESCRIPTION 
     Exemplary embodiments of the present disclosure are illustrated in the drawings, which are illustrative rather than restrictive. No limitation on the scope of the technology, or on the claims that follow, is to be implied or inferred from the examples shown in the drawings and discussed herein. 
     Treatment of many dermatological conditions involve using laser light to heat a target skin area to thermally damage a selected structure within the target skin area and promote a healing response. Consistently accurate delivery of energy to targeted structures to achieve a desired level of damage to the target structure, while minimizing the delivery of energy and corresponding damage to non-targeted structures, has remained an unrealized goal. The present disclosure is directed to providing systems and methods to achieve these objectives. 
     As used herein “target skin area” refers to the skin receiving the energy of a laser pulse. The target skin area may include the surface skin area illuminated by the laser pulse, as well as deeper structures beneath the surface skin area that receive at least a portion of the energy from the laser pulse. As such, “target skin areas” treated by a laser pulse may refer to a volume of skin as opposed to a true area of an outer surface of the epidermis. 
     As used herein, “surface temperature” in reference to a target skin area refers to the temperature of the target skin area as determined or measured at or above the surface of the skin. In particular, where infrared (IR) energy radiated from a target skin area is used to measure the temperature of the skin surface, the surface temperature determination includes energy radiated from deeper in the epidermis in addition to the outermost layer of cells. Without being bound by theory, the strong scattering effects of IR wavelengths within the epidermis limit the energy emitted and detected to the upper 100 microns, and primarily the upper portions thereof. Consequently, “determining a surface temperature” based on detection of radiated IR energy refers to the determination of a composite or average temperature of the upper portions (e.g., tens of microns in depth) of the epidermis, and not merely the outermost layer of skin cells. In embodiments of the present invention, IR-based temperature measurements or determinations provides a reliable and precise determination of the temperature of the uppermost portion of the epidermis. 
     As used herein in connection with optical elements and optical energy, “engages” refers to optical contact between optical energy (e.g., a laser pulse or IR energy) and an optical element such as a lens or a mirror. A laser pulse or IR energy may engage a lens by passing through it, and engages a reflective element by being reflected of its surface. 
     Some exemplary embodiments of the present invention discloses systems and methods using laser handpieces to achieve improved treatments for a variety of medical conditions including, without limitation, acne. In one aspect of the exemplary embodiment, the present disclosure provides laser system having handpieces providing improved skin temperature control to avoid damage to non-targeted structures and more precisely control thermal damage to target structures. In one aspect of the exemplary embodiment, the disclosure provides systems and methods having a laser source, a handpiece to cool and deliver laser pulses to a target skin area, and a temperature determination unit to monitor the target skin temperature. 
     In one embodiment, the handpiece includes optical elements to direct laser pulses to the target tissue along a first optical path, and a temperature determination unit determine the surface temperature of the target tissue using infrared (IR) energy radiated from the tissue along a second optical path. The surface temperature may be determined before, during, or after the delivery of the laser pulses. 
     In one embodiment, the temperature of a target temperature area is determined a plurality of times before and during the delivery of a laser pulse. In preferred embodiments, the first and second optical paths have a common optical axis for at least a portion of each optical path. 
     In one aspect of exemplary embodiments herein, the present invention comprises systems and methods having a handpiece for improved temperature control of a target skin area during the delivery of one or more therapeutic laser pulses in the treatment of a medical condition. The handpiece is configured to facilitate the delivery of laser pulses traveling in a first direction to a target skin area, and to allow IR energy radiated from the target skin area to travel in a second direction generally opposite (“counterdirectional”) to the first direction to detect skin temperature. The handpiece is optically coupled to a laser source adapted to generate at least one, and preferably a plurality, of therapeutic laser pulses for application to the target skin area. The handpiece receives therapeutic laser pulses from the laser source, and includes a cooling window for contacting and cooling a first skin area that includes the target skin area. The cooling window is transmissive to the laser pulses and to IR energy radiated from the target skin area. The laser pulses travel through the handpiece along a first optical path in the first direction, and pass through the cooling window to a target skin area within the first skin area. The system further includes a temperature determination unit that includes a temperature sensing element and a processor for determining a surface temperature of the target skin area based on IR energy radiated from the target skin area through the cooling window along a second optical path travelling along a second optical path generally opposite or counterdirectional to the first optical path. 
     In a preferred embodiment, the first optical path and the second optical path share a common optical axis for at least a portion of their length. The handpiece includes a reflective optical element located in the first optical path and having one of a slot and an aperture through which the laser pulses pass while traveling along the first optical path. The reflective optical element is oriented to receive the IR energy radiated from the target skin area along the second optical path, and to reflect it onto the temperature sensing element. The temperature sensing element is capable of generating a signal that is processed by the processor to determine the surface temperature of the target skin area. 
     In a preferred embodiment, the reflective optical element is precisely oriented to receive IR energy from substantially only the target skin area, and not other adjacent tissue within the larger skin area cooled by the cooling window. The handpiece further comprises at least one second optical element within the first optical path, and the laser pulses engage the at least one second optical element. In a preferred embodiment, the at least one second optical element comprises a plurality of optical elements, including at least one lens and at least one reflective element (e.g., a mirror). In a still more preferred embodiment, the IR energy radiated from the target skin area along the second optical path also engages the plurality of optical elements. In various embodiments, the at least one second optical element may comprise elements for focusing, splitting, redirecting, collimating, or performing other operations on the laser pulses and/or IR energy. 
     In some embodiments, the present invention comprises systems and methods for determining or measuring a surface temperature of a target skin area of a patient during a laser treatment using a handpiece that provides contact cooling of the skin and surface temperature sensing of substantially only a target skin area receiving laser energy. In some embodiments, the present invention provides improved temperature control of a target non-surface (i.e., deeper) structure in the target skin area of a patient during the laser treatment. By providing accurate temperature control of a target skin area during the delivery of laser pulses, the invention provides systems and methods with improved efficacy, safety and/or comfort to patients being treated for a range of dermatological conditions. 
     In some embodiments, the present invention comprises systems and methods for treating the skin of a patient with therapeutic laser pulses with a handpiece that provides contact cooling of the skin and contact sensing to ensure proper contact between the contact cooling element and skin of the patient. In some embodiments, the handpiece further includes temperature sensing based on IR energy radiated from the target skin area receiving the laser pulse(s) and traveling counterdirectionally to the laser pulses. 
     In one aspect, the invention provides systems and methods of controlling a temperature of a target skin area during a laser treatment to avoid one or more of overheating or excessively damaging the target area, underheating the target structure, or causing undesired damage to overlying non-targeted structures. 
     In one aspect, the present invention discloses systems and methods for minimizing the temperature increase of non-target structures overlying a target structure within a target skin area during the delivery of a laser one or a plurality of laser treatment pulses to raise the target structure from a first temperature to a second temperature (e.g., a damage threshold temperature). 
     In various embodiments, systems of the present invention may determine the temperature of a target skin area one or a plurality of times before, during, or after treatment of the target skin area using IR energy radiated from the skin. The laser treatment may comprise comprises one pulse, or a plurality of pulses comprising a single heating episode of the target skin area. As used herein, a “single heating episode” involves a plurality of pulses where the first pulse raises the temperature of the target skin area from a first or baseline temperature immediately prior to the first pulse, and each successive pulse in the heating episode is applied before the target skin area returns to the first or baseline temperature. Where a plurality of pulses is used to heat the target skin area in a single heating episode, the temperature of the target skin area may be determined during a pulse, between pulses, or a combination of during and between pulses of the single heating episode. 
     As used in connection with temperature determinations, “real-time” refers to temperature determinations (e.g., temperature measurements or calculations based on data from an IR temperature sensor) performed with little time delay (e.g., less than 100 msec, more preferably less than 5 msec, most preferably 1 msec or less) between the initiation and conclusion of temperature determination. In some embodiments, real-time temperature determinations refer to temperature determinations that are those made sufficiently rapidly such that they are capable of use by the system to perform one or more tasks, including, but not limited to: terminating a treatment of a target skin area; logging the skin temperature profile vs time to a memory&#39; or providing a warning indication to a user. 
     In one aspect of exemplary embodiments herein, the invention also comprises contact cooling applied to an external surface of a first skin area to enable heating of deeper structures (e.g., a sebaceous gland) to a damage threshold temperature, while minimizing the heating of overlying non-targeted tissue structures. Real-time temperature determinations may occur during before, during, or after the cooling of a first skin area, and may be used (e.g., by a processor executing a treatment algorithm) to perform a responsive action such as initiating, terminating or adjusting the cooling process, initiating or terminating the delivery of one or more laser pulses to a target skin area within the skin area being cooled, or adjusting a parameter of the laser therapy. 
     In one aspect of exemplary embodiments herein, the invention comprises a method of treating a patient having one of more dermatological conditions including, without limitation, abnormal pigmentation conditions, acne vulgaris, dyschromia, hyperhidrosis i.e., excessive sweating), pigmented lesions, vascular lesions, and wrinkles and fine lines by controlled heating of a target skin area from a first surface temperature to a second surface temperature sufficient to cause thermal damage to one or more structures in the target skin area. 
     In one embodiment, the duration of a laser treatment pulse is based on determining the surface temperature of the target skin area one or more times before, during, or after the delivery of laser treatment pulses. In one embodiment, a laser treatment pulse is terminated when the second surface temperature reaches a value indicative of a deeper target structure (e.g., a sweat gland) reaching a desired treatment temperature. The second surface temperature corresponding to the target structure reaching its treatment temperature may be determined prior to treatment, e.g., by thermal (mathematical) modeling of the heating of the target skin area as a function of skin depth based on the parameters of the treatment laser such as wavelength, energy flux, and thermal characteristics of the target skin area such as thermal conductivity, the absorption coefficients of various tissue structures and/or chromophores, etc. 
     In one aspect of exemplary embodiments herein, the invention comprises a method of treating a patient having acne vulgaris by controlled heating of a target skin area from a first surface temperature to a second surface temperature, where the second surface temperature corresponds to a temperature resulting in thermal damage to one of sebum or a sebaceous gland within the target skin area. In one embodiment, the duration of the laser treatment pulse is based on determining the surface temperature of the target skin area a plurality of times during the delivery of one or more laser treatment pulses. In one embodiment, the laser treatment pulse is terminated when the second surface temperature reaches a value indicative of the deeper sebaceous gland reaching a sebaceous gland treatment temperature. The second surface temperature corresponding to the sebaceous gland reaching the sebaceous gland treatment temperature may be identified by thermal modeling as previously discussed. 
       FIG. 1  is a side view illustrating a cross-sectional view of a portion  100  of the skin of a patient, including the outermost epidermis  102 , the middle layer or dermis  104 , and the bottom layer or hypodermis  106 . The epidermis  102  has a thickness of about 80-100 μm, which may vary from patient to patient, and even for a single patient depending upon age, health status, and other factors. The epidermis  102  includes up to five sub-layers (not shown) and acts as an outer barrier. 
     The dermis  104  has a thickness of about 1-5 mm (1000-5000 μm). It contains the blood vessels, nerves, hair follicles, collagen and sweat glands within the skin. Because skin conditions frequently involve structures in the dermis, many laser systems must include sufficient energy to penetrate into the dermis to reach those structures. Those skilled in the art having benefit of the present disclosure would appreciate that careful selection of a number of parameters must be made in the design and construction of laser systems to achieve a desired level of damage to a target structure while minimizing or avoiding damage to non-targeted (e.g., overlying) structures. For example, incorrect selection of the laser wavelength, pulse width, energy per pulse, the use (or nonuse) of a seed laser, or the pump energy of the laser source or amplifier may result in undesired damage and poor performance in treating a dermal structure. Numerous other system choices, such as the use or non-use of an articulating arm for delivery of the laser light to a handpiece for application to the skin, may also affect overall system performance. 
     The lowest layer of the skin is the hypodermis  106 , which includes adipose tissue and collagen. The hypodermis  106  helps control body temperature by insulating the structures of the body below the skin. In addition, the hypodermis protects the inner body tissues from damage by absorbing shock and impacts from outside the body. Because the hypodermis contains fat, its thickness varies widely from person to person based on diet, genetic makeup, and other factors. 
       FIG. 1  depicts a laser beam  108  applied to a target skin area  110  of the skin  100 . The target skin area  110  comprises a surface skin area  112 , as well as underlying skin tissue  114  that absorbs at least a portion of the energy of the laser beam  108 . 
       FIG. 2  is a side view of the skin of a patient illustrating in simplified form, a hair  202  including a hair shaft  204  extending beyond the exterior skin surface  206 . Hair shaft  204  includes a root  208  located below epidermis  210  in the dermis  212 . The base, or papilla, of root  208  is located about  4  mm below exterior skin surface  206 . Root  208  is housed within hair follicle  214  and is surrounded by tissues including connective tissue sheath  216  and blood vessels  218 . Follicle  214  includes a sebaceous gland  219  below an opening  223 . Sebaceous glands such as gland  219  are typically located at depths ranging from about 0.3 mm (300 μm) to about 2.0 mm (2000 μm) below exterior skin surface  206 , but their depth varies depending upon body location. 
     Epidermis  210  includes melanin (not shown), a dark pigment found in tissues of the hair, skin and eyes. Melanin, the primary determinant of skin color, is located within globular structures known as melanosomes, which are produced by skin cells called melanocytes. Darker skin has more melanosomes (and thus more melanin) per unit skin area compared to lighter skin. Laser systems targeting deeper structures such as sebaceous gland  219  in the dermis may present a higher risk of patient discomfort where wavelengths having a relatively high absorption coefficient in melanin are used. Without being bound by theory, when laser light at wavelengths readily absorbed by melanin is applied to darker skin (or dark tattoos having ink particles that absorb laser light at similar wavelengths to melanin), the energy absorbed by the melanin (or tattoo ink particles) attenuates part of the laser energy that otherwise would reach deeper structures, heating the skin of the epidermis and/or upper dermis to a greater degree than lighter/un-tattooed skin. Additional energy—e.g., using higher fluences, higher energy per pulse, or longer treatment times—must be applied to reach and heat deeper structures to a target treatment temperature. However, higher pulse fluences and pulse energy may compound the problem, since the additional energy delivered in a shorter time period will cause the overlying skin temperature to rise even faster than using lower fluences or energies. In addition, longer treatment times can only deliver more energy to the target if the energy is delivered within the TRT of the target tissue—otherwise, the additional energy largely leaks from the target tissue into adjacent non-target tissue. 
     Accordingly, in one aspect of exemplary embodiments herein, the present invention provides laser treatment systems to minimize discomfort by adjusting one or more treatment parameters based on the patient&#39;s skin type. In one embodiment, the invention provides systems and methods comprising a handpiece for determining a skin type of a patient and automatically adjusting one or more treatment parameters based on the skin type of the patient. This may involve, for patients having darker skin types, one or more of: providing additional cooling of the patient&#39;s skin prior to applying a laser therapy to the patient&#39;s skin; lowering a first skin temperature at which a therapy pulse is initiated and applied to the patient&#39;s skin; lowering a fluence of a laser therapy; lowering a peak power of the laser pulses of a laser therapy; providing a longer pulse width of a pulsed laser therapy; and providing a larger beam diameter for a pulsed laser therapy. 
     Those skilled in the art having benefit of the present disclosure would appreciate that successful treatment of acne involves damaging sebocytes, sebum and/or sebaceous glands. This involves heating these structures to damage the gland and/or kill bacteria resident therein. Accordingly, in one embodiment the invention provides laser light at a wavelength that is highly absorbed by sebum, compared to competing skin chromophores (e.g., water), to limit the damage to non-targeted tissue and concentrate the laser energy delivered into the targeted sebaceous gland. Because sebaceous glands are relatively deep structures located in the dermis at depths of 300-2000 μm (0.3-2.0 mm), it is desirable to select a wavelength of light capable of non-ablative penetration to these depths. 
       FIGS. 3A and 3B  are graphs illustrating the absorption curves for several chromophores of interest (water, sebum, and melanosomes) at wavelengths of light for portions of the near-infrared spectrum (about 750 nm-1400 nm) and the short-wavelength IR spectrum (about 1400-3000 nm).  FIG. 3A  illustrates the absorption curve  310  for sebum, the water absorption curve  320 , and the absorption curve  330  for melanosomes. It will be appreciated that in laser treatment systems directed toward conditions other than acne, e.g., tattoo removal or pigmented lesions, the absorption of other chromophores (e.g., inks of various colors, hemoglobin, etc.), skin wrinkle-reduction, etc. will be important considerations in selecting laser treatment system parameters such as wavelength, fluence, peak power, etc. 
       FIG. 3A  demonstrates that the sebum absorption curve  310  has a peak at about 1727.5 nm, meaning that sebum absorbs laser light at this wavelength more strongly than light at other nearby wavelengths, e.g., 1650 nm or 1800 nm. The absorption coefficient of water is less than that of sebum in a range of from about 1693 nm to about 1742 nm, and within a range of from about 2280-2360 nm. The absorption coefficient of melanosomes exceeds that of sebum at all wavelengths less than about 2225 nm, although only by a small amount at the 1727.5 nm peak for sebum, as demonstrated at point  335  of  FIG. 3A , where the two absorptions curves approach one another. It will be appreciated by persons of skill in the art that the concentration of sebum, water, and melanin may vary from patient to patient for a given area, and even within a particular patient depending upon the target tissue structure(s), the hydration status of the patient, and the skin type or area of the patient. 
     As shown more clearly in  FIG. 3B , which is a more detailed illustration of the absorption curves of  FIG. 3A  for the 1600-1800 nm wavelength region using like numbers for like absorption curves and peaks, the absorption coefficient for sebum (curve  310 ) at a peak of about 1727.5 nm (point  335 ) is approximately twice that of water (curve  320 ), and is only slightly less than that of melanosomes (curve  330 ). Specifically, the absorption coefficient for melanosomes at 1727.5 is about 11.0 cm-1, and that of sebum is about 10.3 cm-1. Accordingly, in one embodiment, the invention comprises a laser providing pulsed laser light at a wavelength of between 1693-1742 nm, more preferably at about 1720-1730 nm, and more preferably still at about 1727.5 nm. 
     Referring again to  FIG. 3A , the sebum absorption curve  310  has a further absorption peak ( 340 ) of about 2305 nm, exceeding that of both water and melanosomes at the same wavelength. In one embodiment, the invention comprises a laser providing pulsed laser light at a wavelength of between about 2287-2318 nm. Although sebum strongly absorbs light at 2305 nm, light at this wavelength is less suitable because its penetration depth into skin is much less than that of light at 1727.5 nm. In general, at wavelengths shown in  FIGS. 3A and 3B , the penetration of light decreases with increasing wavelength. Treatment of acne and other conditions with laser light involves multiple tradeoffs, including the relative absorption coefficients of target and non-target tissues/structures, penetration depth of the wavelength of interest into skin, laser power, laser pulse fluence, pulse duration, pulse frequency, etc. 
       FIGS. 4A and 4B  illustrate exemplary temperature profiles of the surface of a target skin area ( FIG. 4A ) and a sebaceous gland ( FIG. 4B ) located below the surface of the target skin area during a laser pulse according to a mathematical model. The laser pulse is intended to raise the temperature of the sebaceous gland to a temperature to achieve a desired cell population death for sebocytes. In this embodiment, the laser pulse is a tophat pulse (i.e., having a uniform intensity profile over the covered area) with a wavelength of 1727.5 nm, a pulse duration of 30 msec, a beam diameter of 2.8 mm, a power of 75 W, a pulse energy of 2.25 J, and a fluence of 37 J/cm2. For purposes of illustration, the skin is depicted as remaining at body temperature for 2 seconds prior to the application of the pulse, although it will be appreciated that any arbitrary time period could be shown. 
     Referring to  FIG. 4A , at time t=2 seconds, a single pulse of laser light having the parameters noted above is initiated and applied to a target skin area, depicted at point  420 . The surface temperature of the skin rises during the pulse, as shown by line  430 , to slightly above 100° C. as shown by peak  440 . After the pulse is terminated, the skin surface temperature of the target area cools rapidly over the next several seconds, as indicated by curve  450 , falling to below 60° C. within 4 seconds (t=6 seconds) after the termination of the pulse. 
       FIG. 4B  illustrates the temperature profile of a sebaceous gland located at a depth of 650 μm below the skin surface in the laser pulse model of  FIG. 4A . As in  FIG. 4A , the skin remains at body temperature for 2 seconds ( 410 ) prior to the initiation of a single pulse ( 421 ) applied to the target skin area. The temperature of the gland rises during the pulse ( 430 ) to a maximum temperature  440  of about 92° C.—less than the surface skin temperature illustrated in  FIG. 4A  due to scattering and the energy absorbed by the overlying tissue. Because the pulse energy at 1727.5 nm is preferentially absorbed by the sebaceous gland (as discussed in connection with  FIGS. 3A and 3B ), comparatively more energy from the laser pulse that reaches the gland is absorbed by the oily tissue therein compared to overlying tissue containing a higher water content. Consequently, the temperature profile ( 450 ) of the sebaceous gland after termination of the pulse at  440  differs significantly from that of the skin surface temperature depicted in  FIG. 4A . Although the temperature initially falls rapidly to about 85° C., the temperature thereafter falls more slowly than the surface temperature shown in  FIG. 4A . 
     The pulse modeled in  FIGS. 4A and 4B  has energy levels below those necessary to ablate skin tissue. Although the pulse will result in thermal damage to the sebaceous gland and could be used to treat acne, temperatures above 45-50° C. are likely to result in significant discomfort when they persist, as illustrated in  FIG. 4A , for 4 seconds or longer. Accordingly, the pulse depicted in  FIG. 4A  would have limited application as a viable treatment to most patients. In one embodiment, the laser pulses described in connection with  FIGS. 4A and 4B  result in temperatures too high to be used for treatment, although they could be modified (e.g., by lowering pulse fluences, shortening pulse treatment times, etc.) to result in skin temperatures more suitable for treatment. In one embodiment, temperatures may be lowered by skin cooling, as described in connection with  FIGS. 5A and 5B . 
       FIGS. 5A and 5B  illustrate exemplary temperature profiles of a target skin area during a laser pulse according to a different mathematical model than those of  FIGS. 4A-B . In the embodiment of  FIGS. 5A and 5B , the laser pulse has the same parameters as those of  FIGS. 4A-B  (wavelength A=1727.5 nm; pulse duration=30 msec; beam diameter=2.8 mm, power=75 W; pulse energy=2.25 J; fluence=37 J/cm2). However, in  FIGS. 5A and 5B  the target skin area is cooled prior to, during, and after the application of the laser pulse. 
     Although many known methods and modes of precooling the skin may be used, the embodiment of  FIGS. 5A and 5B  are modeled on a system having a contact cooling element applied to a first skin area that includes a target skin area to be treated by the laser pulse. The contact cooling element includes a cooling window that, in some embodiments, directly contacts the first skin area, and the target skin area actually irradiated by the laser pulse is wholly located within the first skin area. Although a variety of materials may be used as the contact cooling window, in the embodiment of  FIGS. 5A and 5B , the cooling system includes a sapphire cooling window cooled by a thermoelectrical cooler (TEC) coupled to the window. The sapphire cooling window has a thickness of 3 mm and a diameter of 1 inch (25.4 mm), although many different sizes, shapes, thicknesses, and materials may be used different embodiments. For example, although the cooling window modeled in the embodiment of  FIGS. 5A and 5B  was circular, other cooling window shapes such as square, rectangular, or other polygonal or nonpolygonal shapes could be used in different embodiments and for different tissue types. The cooling window was modeled as being cooled to a temperature of 5° C. 
     In alternative embodiments, non-contact cooling systems (e.g., cold air or other fluid circulated onto or across the surface of a target skin area) may be used to cool the skin. However, it is believed that the thermal resistivity of the skin, and the thermal coupling between the skin and gases such as air, typically preclude non-contact systems from providing adequate cooling capacity during the delivery of laser pulses to both effectively treat deeper target structures and prevent the skin surface from reaching temperatures likely to result in significant discomfort. Accordingly, contact cooling systems are preferred. In other embodiments, evaporative cooling systems (e.g., sprayed coolant evaporating from the skin) may be used. 
     In  FIG. 5A , the contact cooling element at 5° C. is applied to the skin at time t=0, and skin temperature falls rapidly along curve  510  to a target temperature of about 10° C. at time t=2 second, at which point ( 520 ) the laser pulse is applied to the skin. Delivery of the laser pulse to the target skin area is continued until a target surface temperature  560  of the target skin area is reached ( 540 ), at which point the laser pulse is terminated. Because the contact cooling element continues to cool the skin both during and after the laser pulse, the surface temperature falls rapidly along curve  550  after laser pulse termination. 
       FIG. 5B  illustrates the temperature profile of a sebaceous gland located at a depth of 650 μm below the skin surface in the cooling and laser pulse delivery process of  FIG. 5A . When contact cooling is applied to the skin at time t=0, the temperature of the gland declines (curve  510 ), but much less rapidly than the surface temperature, depicted in  FIG. 5A . The laser pulse is initiated at point  520 , and the temperature of the gland rises along line  530  until the laser pulse is terminated ( 540 ). The gland temperature thereafter falls along line  550 , but less rapidly than the surface temperature decline following the pulse termination in  FIG. 5A . 
     Because direct measurement of the gland temperature is difficult or impossible given its depth within the skin, in embodiments of the present invention, surface skin temperature may be monitored as an indirect indication of the gland temperature. Those skilled in the art having benefit of the present disclosure would appreciate that because the goal of the laser treatment is to heat the sebaceous gland to a damage threshold temperature, cooling the gland (as opposed to the skin surface) shown by curve  510  in  FIG. 5B  is undesirable, but is an unavoidable consequence of the protective precooling of the overlying skin tissue. Precooling the overlying skin tissue to a desired surface temperature of about 10° C., as shown in  FIG. 5A , generates a downward cooling wave or thermal gradient in the target skin area, propagating from the skin surface toward the deeper tissues in the dermis and hypodermis. The precooling process may be controlled such that, for a sebaceous gland in a known depth range, when the laser pulse is delivered to heat the target skin area, the precooled overlying skin remains below a damage threshold temperature while the target sebaceous gland reaches (or exceeds) a damage threshold temperature. This is facilitated by selecting a laser wavelength for which the absorption coefficient of sebum/sebaceous gland tissue exceeds that of water, the primary chromophore of most of the overlying dermal and epidermal tissue. 
     Comparing  FIGS. 5A and 5B , precooling the skin allows the sebaceous gland to reach a temperature of about 78° C. at the termination of the laser pulse—about 13° C. above the surface temperature of target skin area at the surface (about 62° C.). Although the overlying tissue is unavoidably heated during pulse delivery, careful precooling before initiating the laser pulse allows the surface temperature to be precooled to a temperature well below the sebaceous gland at pulse initiation (about 10° C. for the skin surface vs. about 22° C. for the sebaceous gland as shown by  FIGS. 5A and 5B  at point  520 ). This temperature difference occurs because the cooling window creates a thermal gradient between the skin surface and deeper structures as heat is removed. In addition, the pulse energy at a wavelength of 1727.5 nm is more highly absorbed by the sebaceous gland than overlying tissue. Because of the selective precooling and differential absorption between the surface and the sebaceous gland provided by embodiments of the present invention, the non-targeted overlying tissue is heated by the laser pulse to a lower temperature (about 63° C.,  FIG. 5A  at point  540 ) than the targeted sebaceous gland (about 81° C.,  FIG. 5B  at point  540 ), reducing or minimizing damage to the non-targeted tissue and patient discomfort. 
     In some embodiments, the present invention includes a method of controlling the duration of a pulse to limit the surface temperature of a target skin area to a desired or target threshold using a handpiece capable of contact cooling and rapid, real-time temperature measurement of the skin during the delivery of one or more laser pulses.  FIG. 5C  demonstrates a method of achieving such control by monitoring the temperature of a pulse during the delivery of a single pulse. The surface temperature of the skin may be determined one or more times during pulse delivery, and the pulse may be terminated based on one or more of the skin temperatures. In one embodiment, the skin temperature is periodically determined during the pulse delivery, and the pulse is terminated when the surface skin temperature reaches (or is within a desired interval of) a threshold temperature. 
       FIG. 5C , illustrates a surface temperature profile during the delivery of the laser pulse of  FIG. 5A . From time t=1.99 to t=2.00 seconds, the temperature of the skin near the surface (modeled in  FIG. 5C  at a depth of 100 μm) is relatively constant at about 10° C. (line  510 ). At time t=2.00 seconds ( 520 ), the pulse is initiated and applied to the skin through the cooling window. Simultaneously, the first of a plurality of surface temperature determinations of the target skin area  570  is made. Pulse delivery continues along line  530 , and the surface temperature rises until the pulse is terminated at  540 . After pulse termination, the surface temperature falls as indicated by line  550 . During pulse delivery, multiple temperature determinations  570  are made at equal intervals, although the frequency of temperature sampling may vary based on a variety of factors such as the time frame desired for heating the tissue, thermal relaxation time of the target structure, pulse fluence, pulse power, pulse wavelength, and exogenous factors such as the target structure damage threshold, and other factors. Temperature determinations may be performed at a desired sampling interval, e.g., 100 msec or less (i.e., 10 or more temperature determinations per second) and may occur at uniform or non-uniform time intervals, e.g., varying based on the difference between a measured temperature and a desired threshold, or on other exogenous factors. In one embodiment, the temperature sampling interval is increased as the surface skin temperature approaches a desired temperature. Depending upon the sensing element and processor used, the surface temperature may be determined at a sampling or time interval of 0.001-100.0 msec (i.e., 1-100,000 μsec, or performing 10 to 1 million temperature determinations per second). 
       FIGS. 5A and 5B  illustrate methods of treating a sebaceous gland according to one embodiment of the present invention. Additional details of treating a sebaceous glans may be found in U.S. Pat. No. 10,864,380, which is incorporated herein by reference. However, embodiments of the present invention may be used to treat other structures in the dermis or hypodermis (e.g., sweat glands, hair follicles, etc.) by facilitating precise control of surface and deeper temperatures within a target skin area. 
       FIG. 6A  is a schematic illustration, in block diagram form, of an embodiment of a therapeutic laser system  600  having a handpiece with contact cooling and temperature sensing for providing therapeutic laser pulses along a first optical path that is coaxial with a second optical path for sensing skin temperature for at least a portion of the first and second optical paths. A laser  610 , which is preferably a semiconductor laser, provides laser pulses having a wavelength with a high absorption coefficient in a target tissue. The target tissue may be sebaceous gland tissue, sweat gland tissue, fat, or other tissue. Laser  610  is optically coupled, e.g., by an optical fiber, articulating arm, or other optical coupling elements known in the art, to a handpiece  620  for delivery of one or more laser pulses to a target skin area. Although semiconductor (e.g., diode) lasers are preferred, it will be appreciated that other laser types (e.g., fiber lasers, dye lasers, etc.) may be used in different embodiments. 
     Handpiece  620  includes a cooling system  622  for cooling a first skin area that includes a target skin area within the first skin area. Cooling system  622  includes a contact cooling element comprising a cooling window  628  maintained in a fixed position in contact with a heatsink portion of a thermoelectric cooler (TEC)  630  by a window frame  626 . Cooling window  628  may comprise any of a variety of IR-transmissive materials, including for example, sapphire, ZnS, diamond, ZnSe, and other thermally conductive material that are transmissive to infrared light. In alternative embodiments (not shown), the contact cooling element may comprise components or structures in addition to cooling window  628 , such as a copper (or other material having a high thermal conductivity) cooling element that is not light-transmissive to provide additional cooling capacity. 
     In some embodiments, TEC  630  may be a Peltier-type cooler and has a warm side and a cold side (not shown). The heatsink portion of the TEC  630  is part of the cold side and is used to remove heat from the cooling window  628  to maintain the cooling window at desired temperature as it contacts the first skin area. A cooling medium  632  removes heat from the hot side of the TEC  630  to prevent heat buildup in handpiece  620 . In one embodiment, the cooling medium comprises circulating cold water, although other thermally conductive fluids or other materials may be used in different embodiments. In preferred embodiments, the cooling medium is circulated to and from TEC  630  from a reservoir (not shown) that is not part of the handpiece. 
     To ensure efficient skin cooling, it is necessary to maintain good contact between the skin and the cooling window  628  during treatment. In two alternative embodiments (see  FIGS. 11A-11D ; and  FIGS. 12A-12B ), the invention comprises a laser treatment system including a handpiece having one or more contact sensing elements to detect when the cooling window  628  is properly in contact with the first skin area. The contact sensing element(s) may be coupled to, or separate from, cooling window  628  and/or frame  626  (e.g., a heatsink surrounding the cooling window periphery), and may comprise, e.g., one or more electrical contacts capable of sensing electrical activity, conductivity, or resistance of the skin indicative of adequate skin/cooling window contact. Other contact sensing elements (e.g., ultrasonic sensors) detecting different skin parameters or features associated with proper contact (e.g., force, vibration, pressure, temperature, the presence of sweat or skin oils) may also be used. 
     One or more skin contact indicators ( FIGS. 11A-D , and  12 A-B) may alert a user to the contact status between the skin and cooling window  628 . The skin contact indicator may indicate when the contact element(s) are—or are not—in good contact with the first skin area and may prompt the user to manipulate the handpiece to restore good contact when necessary. The skin contact indicator(s) may comprise, e.g., an LED indicator on handpiece  620  that displays a first color when good skin contact exists and a second color when the window  628  is not in proper contact with the skin. Other indicators, such as an audible sound or alarm, may also be provided, and the system may be interlocked such that the system will not apply (or will terminate) a laser pulse if good contact between the cooling window  268  and the skin is absent. 
     Handpiece  620  may further include a temperature determination unit (TDU)  624  for determining a surface temperature of the target skin area. TDU  624  may, in various embodiments, sense the temperature of the target skin area one or more times before (e.g., during a precooling step), during, or after (e.g., during a postcooling step) laser pulse delivery. During delivery laser pulse(s) to a target skin area, the skin surface temperature may be influenced by two different heating mechanisms, including energy absorbed directly from the laser, and thermal bloom resulting from energy conducted from deeper skin tissue as the thermal energy absorbed by deeper structures relaxes into the environment. Thermal bloom from deeper structures back to the skin surface may be a significant cause of epidermal damage in laser systems targeting relatively deep structures such as sebaceous or sweat glands. Therapeutic laser systems such as system  600  enable improved treatment outcomes by ensuring that the surface temperature of a target skin area remains below a desired surface temperature even while heating deeper structures to higher temperatures, minimizing both skin damage and patient discomfort. 
     Temperature determination unit (TD)  624  may comprise a temperature sensing element for generating a first signal indicative of skin surface temperature, and a processor for processing the first signal to determine the surface temperature. TDU  624  may sense the surface temperature of the target skin area one or more times before, during, or after delivery of laser pulse(s) from laser  610 . TDU  624  may be capable of sensing the surface temperature of the target skin area at from 10 to 1 million times per second. In one embodiment, the temperature sensing element of TDU  624  comprises an infrared (IR) radiation detector, shown in  FIG. 9A , to detect IR energy radiating from the surface of the target skin area through the cooling window  628 , and a processor (e.g., controller  640  as discussed below) to determine the surface temperature of the target skin area based on data received from the temperature determination unit  624 . It will be appreciated that non-IR temperature sensors (e.g., an electrical temperature sensor)  624  may be used. In the embodiment of  FIG. 6A , TDU  624  is a part of the handpiece  620 . In some embodiments, the temperature sensing element, the processor, or the entire TDU  624  may be located outside the handpiece. In preferred embodiments, an IR temperature sensing element is provided as part of the handpiece  620 . 
     Handpiece  620  may also include a plurality of optical elements  634  to sequentially direct laser pulses along a first optical path within the handpiece to a target skin area, and to direct IR energy from the target skin area along a second optical path that is coaxial with and generally counterdirectional to the first optical path for at least a portion of both optical paths. Additional details on embodiments of the optical elements are provided in connection with  FIGS. 9A-9F . To facilitate the counterdirectional flow of laser and IR energy, the handpiece comprises a first optical element (not shown) having a first open area through which the first optical path passes, i.e., the laser pulses do not substantially engage the first optical element, and pass through the first open area. In contrast to the laser pulses, however, the IR energy does engage the first optical element, which is preferably a reflective optical element (e.g., a mirror). The first optical element directs the IR energy from the target skin area to the temperature sensing element in TDU  624 . The signal from the temperature sensing element is processed to determine skin surface temperature at a desired rate of from  10  to  1  million times per second. 
     The plurality of optical elements  634  in handpiece  620  also includes at least one second optical element (not shown), and more preferably a plurality of second optical elements, that are engaged by the laser pulses and/or IR energy from the target skin area. In one embodiment, shown in more detail in  FIGS. 9A-9F , the at least one second optical element comprises eight (8) optical elements, with the first optical path (i.e., the laser pulse path) engaging all eight optical elements, and the second optical path engaging five of the optical elements in addition to the first optical element. The optical elements may include one or more of lenses (e.g., plano-convex lenses, turning mirrors, meniscus lenses, aspherical lenses, flat lenses, etc.), mirrors (e.g., aspherical mirrors), or other optical elements (e.g., optical parametric oscillators) to direct the laser pulses received from the optical laser source (e.g., via an optical fiber cable) to a target skin area. In preferred embodiments, the at least one second optical element comprises a plurality of lenses (e.g., at least three lenses) and at least one mirror, and the first and second optical paths engage at least two lenses and the last least one mirror. The optical elements  634  may in various embodiments concentrate the laser energy to a single target skin area, or may include beam-splitting elements to split each pulse beam into multiple beams to treat a plurality of target skin areas simultaneously. 
     In one embodiment (see  FIGS. 7, 9C, 9E, 9G ), the plurality of optical elements  634  includes a movable scanning mirror capable of movement to direct laser pulses to different target skin areas within a first skin area cooled by cooling window  628 . The movable scanning mirror also limits IR energy received by TDU  624  to IR energy from substantially only the target skin area to which the laser is directed at any given time, i.e., it eliminates IR light from other skin areas within the larger first skin area cooled by cooling window  628 , which is significantly larger than a single target skin area. In embodiments including a movable scanning mirror, after a first target skin area is treated by one or more laser pulses, the scanning mirror is repositioned to direct subsequent pulses to a new (i.e., second, third, etc.) target skin area within the larger first skin area cooled by the cooling window  628 . When a desired number of target skin areas have been treated at a single cooling window position, the user may reposition the cooling window  628  to a new position covering a new skin area, and a different group of target skin areas within the new skin area may be treated by laser  610  using scanner in handpiece  620 . In one embodiment, the position of the movable scanning mirror may be adjusted on two or more axes, e.g., by one or more motors, thereby directing succeeding pulses to different target skin areas within the first skin area, enabling treatment of a relatively high proportion of the total area in contact with the cooling window. In alternative embodiments, the plurality of optical elements  634  may not include a scanner. 
     Referring again to  FIG. 6 , system  600  further includes a controller  640 , which may comprise one or more processing elements such as microprocessors, microcontrollers, field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), etc. to control the operations of the laser treatment system. 
     Controller  640  may include a pulse timing control unit  642  that controls the timing of the laser pulses from laser  610 , including initiating the pulse at a first timepoint and terminating the pulse at a second timepoint. The pulse timing control unit  642  may receive data from temperature sensor  624 , and may initiate the therapeutic laser pulse at a first timepoint based on, e.g., a manual signal from a user or a determination that target skin area has been cooled to a desired surface temperature (e.g., 15° C., 10° C., 5° C., 0° C., −5° C., −10° C., etc.). Pulse timing control unit  642  may also terminate the therapeutic laser pulse at a second timepoint based on, e.g., a predetermined pulsewidth or a determination that the surface temperature of the target skin area has reached a threshold surface temperature (e.g., indicating that a deeper target structure such as a sebaceous gland has reached a damage threshold temperature, e.g., 60° C.-75° C.). 
     Controller  640  may also include a temperature sensing control unit  644  that controls the operation of the TDU  624 . Temperature sensing control unit  644  ensures that the TDU  624  determines the surface temperature of a target skin area at a desired (e.g., programmed or predetermined) sampling rate such as 10 or more times per second. Controller  640  may synchronize the operations of the temperature sensing control unit  644  with the pulse timing control unit  642 . 
     In one embodiment, the pulse timing control unit  642  and the temperature sensing control unit  644  may comprise one or more of software, firmware, or other programming code operating in the controller  640 . In one embodiment, the pulse timing control unit  642  and the temperature sensing control unit  644  may comprise separate processors or sub-processors, and/or separate executable code programs comprising one or more of software, firmware, etc., within controller  640 . A wide variety of hardware and software designs may be used to achieve the functions described herein, and all are considered as within the scope of the present disclosure. 
     Controller  640  may also control other operations within the therapeutic laser treatment system  600  (e.g., software and firmware units and subunits, timers, mechanical or electrical elements or subsystems, etc.). These functions may also include, without limitation, control of the positioning of a movable scanning mirror for determining a target skin area, as discussed above and in greater detail in connection with  FIGS. 7 and 9A-9F . Controller  640  also controls the operation of cooling system  622 , including without limitation the temperature at which the cooling window is maintained (which may be determined by a user or by the patient&#39;s skin type as described in connection with FIG.  6 B), the cooling capacity (i.e., the thermal energy removal rate of the TEC), status alarms, etc. 
     A user interface  650  is preferably provided to allow a system user to select or program one or more parameters (e.g., beam diameter or spot size, fluence, wavelength, target temperature of the surface of the target skin area, cooling temperature of the target skin area at which a pulse may be delivered, etc.) to control the operation of therapeutic laser system  600 . User interface  650  may also display various status indicators and data associated with the system and/or a treatment session, such as the current laser parameters, duration of treatment, number of pulses delivered, etc. Controller  640  may also receive and process inputs from the user interface  650 , and provide outputs to the user interface. In alternative embodiments, the user interface may be omitted. 
     Finally, the system  600  includes a power supply  660  for providing power to one or more of the foregoing portions of the system. In one embodiment, power supply  660  may comprise a power supply coupled to a standard NC power outlet to convert AC to DC power at one or more voltages, and may include a battery (e.g., for backup in the event of a power outage), a supercapacitor, etc. Power supply  660  also provides power to controller  640 , which in turn includes a current-controlled power supply for driving the laser  610  and/or other system components and subassemblies at rapid switching rates based on inputs from pulse timing control unit  642 , temperature sensing control unit  644 , cooling system  622 , temperature sensor  24 , and scanner  634 . 
     One or more elements illustrated in  FIG. 6A  may be comprised of hardware, software, firmware, and/or a combination thereof. 
       FIG. 6B  is a block diagram of an alternative embodiment of therapeutic laser system  600  of  FIG. 6A . The therapeutic laser system of  FIG. 6B  is capable of determining the skin type of a patient, and adjusting one or more treatment parameters based thereon. Like numbers are used for like elements in  FIGS. 6A and 6B , and the discussion of  FIG. 6B  omits or limits previously discussed elements of  FIG. 6A  for brevity and to avoid repetition. Elements previously described in connection with  FIG. 6A  will have similar functions in  FIG. 6B . 
     The system of  FIG. 6B  allows one or more treatment parameters of the system  600  to be adjusted to minimize discomfort and/or pain to patients that may result from differences in skin type. Handpiece  620  includes a skin typing light source  636  for applying a multi-wavelength light signal to determine a skin type of the patient. Although different skin typing systems may be used, in one embodiment the system  600  of  FIG. 6B  determines a Fitzpatrick skin type of the patient. Skin typing light source  636  may generate noncoherent, multi-wavelength light in one or more of the visible and IR light ranges. A skin typing light sensor  638  is provided to sense a portion of the light from light source  636  that is reflected from the skin of the patient. 
     Controller  640  includes a skin type determination unit  646  that receives data from the skin typing light sensor  638  relating to, e.g., the absorbance or non-absorbance of the patient&#39;s skin of particular wavelengths of light from the skin typing light source  636 . The skin type determination unit  646  analyzes the absorbance/non-absorbance data and determines a skin type of the patient. Controller  640  includes logic (e.g., executable software or firmware code, not shown) to modify one or more aspects of the laser treatment based on the patient&#39;s skin type to maintaining the skin surface temperature below a desired maximum during treatment. 
     Without being bound by theory, patients with darker skin (i.e., a higher melanin content than lighter skin) may experience a more rapid temperature rise as relatively more energy from laser pulses is absorbed by the more highly concentrated melanin particles. To avoid an excessive temperature (and an increased risk of patient discomfort/pain), controller  640  may, for example, provide additional cooling (i.e., longer cooling time) for patients with darker skin; lower a target skin temperature at which a therapy pulse is or may be initiated (e.g., automatically initiating therapy or providing a prompt to a user when the skin is cooled to 5° C. for patients with darker skin instead of 10° C. for lighter-skin patients); lower a fluence of the laser pulses to deliver less energy per unit time for darker skin patients; or lower a peak power of the laser pulses of a laser therapy. The controller may also modify or change other parameters such as laser pulse duration and laser spot size to ensure efficacious surface temperature control in the treatment of a wide range of skin types. 
     The therapeutic laser system of  FIG. 6B  is also capable of insuring that the handpiece  900 ,  1100 ,  1200  shown in  FIGS. 9, 11, and 12  includes a mechanism for assisting the user with properly positioning the handpiece against the skin of the patient. For example, in one embodiment, the controller  600  includes a contact sensing controller  645 . The contact sensing controller  645  is generally configured to interact with a contact sensing unit  625  to determine when the handpiece is oriented with substantially planar contact with the skin of the patient and/or to sense when the handpiece is pressed onto the skin of the patient with sufficient pressure and/or force to cause the laser pulses to properly cool a first skin area in contact with the contact window, and to heat the target skin areas within the first skin area to a desired temperature and with a desired distribution. The contact sensing controller  645  may be configured to communicate with the user of the handpiece via a contact indicator  652 , such as by communicating that planar contact has been established and/or that sufficient pressure/force is being applied between the handpiece (e.g., via the contact window) and the skin of the patient. The contact sensing unit  625  may include a plurality of contact sensing elements  627  located on the frame  626 , which may take the form of mechanical or optical sensing elements, as discussed more fully in connection with  FIGS. 9, 11, and 12 . 
       FIGS. 6A and 6B  illustrate a system according to certain embodiments of the invention involving cooling the skin before, during, and after pulse delivery. Alternative embodiments of the invention include systems with no cooling of the skin, or without cooling of the skin during one or more of the periods before, during, and after delivery of the therapeutic laser pulse. Additional alternative embodiments include systems in which different cooling capacities (i.e., rate of heat removal from the skin) are used in the periods before, during, or after delivery of the laser pulse, and during portions of these periods. 
     One or more elements illustrated in  FIG. 6B  may be comprised of hardware, software, firmware, and/or a combination thereof 
       FIG. 7  is a simplified sectional view of the interior of one embodiment of a handpiece  700  for cooling a first skin area  730 , applying laser pulses to one or more target skin areas within the first skin area, and determining the surface temperature of the target skin area(s). Laser pulses, visually shown as a laser beam  720  at an instant of time, are delivered to the handpiece  700  via an optical fiber  740  from a diode laser (e.g., laser  610  of  FIG. 6 ). After exiting optical fiber  740 , pulses  720  pass along a first optical path through focusing lenses  770  and an aperture in a temperature detection mirror  780 . Pulses  720  are redirected by a scanning mirror  760 , and pass through a cooling window  710  to a target skin area within a first skin area cooled by the cooling window. Scanning mirror  760  may be controllable (e.g., by a motor) and repositionable such that one or more laser pulses  720  are sequentially directed to a series of target skin areas within the cooling window, without moving the cooling window  710  to contact a different area of skin  730 . Scanning mirror  760  also receives IR energy traveling from substantially only the target skin area, and excludes IR energy from other (i.e., non-target) areas within the first skin area. The IR energy from the target skin area (not shown) travels along a second optical path generally counterdirectional to the first optical path, and may occur simultaneously with the delivery of a laser pulse. 
     Handpiece  700  also includes a thermoelectric cooler  750 , which includes a heatsink portion (not shown) in contact with cooling window  710  to maintain the cooling window at a desired (e.g., programmed) temperature during contact with the first skin area  730 . Cooling window  710  preferably cools the first skin area from a first surface temperature (e.g., body temperature) to a second surface temperature before laser pulses  720  are applied to the skin. In one embodiment, the first skin area is cooled before, during, and after application of a laser pulse thereto. 
     Skin temperatures may be detected by infrared energy radiated generally counterdirectionally to the laser pulses from the target skin area through the cooling window  710 . This infrared energy is reflected by scanning mirror  760  onto temperature detector mirror  780 , which focuses the infrared energy on a detection element (not shown), which generates a temperature signal processed by a processor to determine the temperature of the target skin area at a desired sampling rate. 
       FIG. 8  is a simplified partial exploded, external view of a handpiece  800  for cooling skin and applying laser pulses thereto. In one embodiment, the internal components of  FIG. 7  may be enclosed within a housing  805 . A cooling window  810  (which may be the same as cooling window  710  of  FIG. 7 ) is maintained in contact with a cooling heatsink  820  (which may be the same as heatsink of TEC  750  of  FIG. 7 ) by a window frame  830 , which has no thermal function and merely maintains cooling window  810  in contact with heatsink portion  820 . It will be appreciated that additional or alternative components may be included in the handpiece of  FIGS. 7 and 8 , and that other similar handpiece configurations and geometries may be used to provide a handpiece providing skin cooling and laser pulse delivery along a first optical path as well as skin temperature determination and monitoring by IR energy traveling along a second optical path generally counterdirectional to the first optical path. 
       FIGS. 9A-9F  are perspective ( 9 A,  9 B), optical schematic ( 9 D,  9 F), and exploded ( 9 C,  9 E,  9 G) views, respectively, of one embodiment of a handpiece  900  for providing laser therapy to a patient&#39;s skin as part of a laser treatment system. The handpiece  900  provides contact cooling of the skin, and senses skin temperature from IR energy emitted by the skin along a second optical path that is at least partially coaxial with the first optical path traveled by the laser pulses. By sensing temperature along an optical path that is partially coaxial with the laser pulse path, greater accuracy is achieved in sensing the temperature of only the target skin area—i.e., the skin actually receiving the energy of a laser pulse—as opposed to adjacent tissues not receiving laser energy. This is achieved by sensing IR energy from the skin through the contact cooling window, and by using optical elements that limit the IR energy received by the temperature sensor (and used to determine skin temperature) to substantially only IR energy emitted by the target skin area. Because the temperature determination is based only on IR energy emitted from the target tissue actually receiving the laser pulses, and not on IR energy emitted from adjacent non-target tissue that does not receive laser pulse energy, the temperature of the target skin area is obtained with high accuracy. 
       FIGS. 9A and 9B  are perspective views of the handpiece  900 , which includes a proximal end  902  and a distal end  904 , and comprises a housing  910  having a shape adapted for holding by a user (e.g., a physician or technician), and having an inner volume shielding a plurality of optical elements, discussed more fully below in connection with  FIGS. 9C, 9E, and 9G ). An optical cable  905 , which comprises an optical fiber core (not shown), is coupled to the proximal end  902  of the handpiece  900 . Optical cable  905  is coupled to a laser source (not shown) which generates and delivers laser pulses to the handpiece  900  through the cable. Optical cable  905 , and specifically the optical fiber therein, terminates inside the proximal end  902  of handpiece  900  in a standard optical coupler  907  ( FIGS. 9C, 9E, and 9G ) such as an SMA coupler, although other standard optical couplings may be used. 
     At the distal end  904  of the handpiece  900 , a contact cooling unit  915  includes a cooling window  920  to cool, by direct contact, a first skin area equal in size to the cooling window. In addition to the cooling window  920 , contact cooling unit  915  also comprises other elements more fully shown in  FIG. 9C , including a cooling window heatsink  916  that surrounds the cooling window  920 , a thermoelectric cooler (TEC)  917 , and a second heat sink  918 . Laser pulses from optical cable  905  pass through handpiece  900  along a first optical path and are applied to a target skin area, which comprises a smaller skin area within the first skin area cooled by the cooling window. 
     As shown in  FIG. 9B , housing  910  of handpiece  900  includes an optical aperture or port  914  through which laser pulses exit the housing and travel along the first optical path through the cooling window  920  to the target skin area. Cooling window  920  is spaced a desired distance from housing  910  by cooling unit  915 , which also functions as a spacing member to allow a user to visualize the area being cooled and treated by the handpiece  900 . 
       FIG. 9C  is a partially exploded view of the interior portion of handpiece  900  with housing  910  removed, showing in greater detail the optical elements, contact cooling unit, and temperature determination unit included in the handpiece  900 . In alternative embodiments, the temperature determination unit may be separate from the handpiece  900 . The handpiece  900  includes a plurality of optical elements  925 ,  930 ,  923 ,  934 ,  936 ,  938 ,  940 ,  942 , and  944  within the housing  910 , although in alternate embodiments one or more optical elements by be located outside the housing. Different combinations of these optical elements each define the first optical path taken by laser pulses  908  to the target skin area ( FIG. 9D ) and the second optical path taken by the IR energy from the target skin area to a temperature sensing element  950  ( FIG. 9E ). 
       FIG. 9C  also shows additional details of contact cooling unit  915 , which includes a cooling window heatsink  916  surrounding the cooing window  920 . Heat is removed from the skin by direct contact between the first skin area and the cooling window  920 , and is passed to the heatsink  918 , which is coupled to the cool side of a TEC  917  to maintain the cooling window  920  at a desired temperature (e.g., a user selectable temperature in the range of −10° C. to 25° C.). TEC  917  passes heat received on its cool side from cooling window  920  via cooling window heatsink  916  to its hot side, and is removed from the TEC hot side by a second heatsink  918 , which is coupled to a circulating cooling medium (not shown) such as water. 
     The handpiece  900  of  FIG. 9C  includes a temperature determination unit, which may be a temperature determination unit  624  as shown in  FIG. 6 . Although the temperature determination unit of  FIGS. 6 and 9C  is part of handpiece  900 , in alternative embodiments, all or portions of the temperature determination unit may be located outside of handpiece  900 . Referring again to  FIG. 9C , handpiece  900  includes a temperature sensing element  950  for receiving IR energy emitted from the target skin area through the contact window  920  along a second optical path generally counterdirectional to the first optical path taken by laser pulses  908 . The first and second optical paths share a common optical axis for at least a portion of their lengths. In response to receiving IR energy from the target skin area, temperature determination unit determines the surface temperature of the target skin area one or more times before, during, or after the application of the at least one therapeutic laser pulses. Temperature sensing element  950  generates a signal indicative of the temperature of the target skin area, and is coupled to a processor (not shown) which receives and processes the signal to determine the surface temperature of the target skin area at a desired rate (e.g., 10-1 million times per second). The temperature determination unit that may determine or measure surface temperature of the target skin area before during, or after treatment with laser pulses  908 . Operation of the temperature determination unit may be controlled by a temperature sensing control unit  644  ( FIG. 6 ). 
       FIG. 9D  is an optical schematic showing the optical path taken by the laser pulses  908  in passing through the handpiece to the target skin area, and the optical elements that the laser pulses engage (e.g., lenses through which a laser pulse passes or mirrors reflecting the pulses).  FIG. 9D  shows a laser pulse beam  908  exiting the optical fiber coupling  907  and passing through three plano-convex lenses  930 ,  932 ,  934  before being reflected by a turning mirror  936 . Plano-convex lenses  930 ,  932 ,  934  in the embodiment of  FIG. 9D  comprising BK7, fused silica lenses, although many different lens types may be used. In an alternative embodiment, lenses  930 ,  932 , and  934  may be replaced by a single aspherical lens (not shown). Although fixed in position in the embodiment of  FIG. 9D , turning mirror  936  in alternative embodiments may comprise a steerable mirror that is adjustable to change the angle of reflection. 
     After the laser pulse beam  908  is reflected by turning mirror  936 , it passes through another plano-convex lens  938  and is reflected by a beam steering element comprising a movable turning mirror  940  that is movable or adjustable on two axes by motors, also known as a “scanning mirror.” By moving the position of the mirror, succeeding pulses may be directed to different target skin areas within the first skin area cooled by the cooling window  920 . In alternative embodiments, beam steering elements different from or in addition to the movable turning mirror  940  may be used. Plano-convex lens  938  is made of ZnSe in one embodiment, although other materials may be used in different embodiments. Movable turning mirror  940  reflects the laser pulse beam  908  through a meniscus lens  942  and a plano-convex lens  944  before passing through cooling window  920 . Meniscus lens  942  and plano-convex lens  944  comprise ZnSe in one embodiment, but may be made of different materials in alternative embodiments. In a further alternative embodiment, lenses  938 ,  942 , and  944  together may be replaced by a single aspherical lens (not shown). Cooling window  920  is made of a material that is transmissive to both laser light at the wavelength(s) output by the laser source as well as IR light emitted from the target skin area. In one embodiment, cooling window  920  is made of sapphire. In alternative embodiments, ZnS, diamond, or ZnSe may be used successive. 
       FIG. 9E  is the partially exploded view of the interior portion of handpiece  900  shown in  FIG. 9C , but includes added lines showing an exemplary laser pulse  908  to illustrate the first optical path traveled by such a pulse. For brevity, discussion of the optical elements already noted in  FIG. 9C  is omitted. As can be seen, the laser pulse  908  initially follow a path having a linear optical axis from optical coupler  907  to the turning mirror  936 . Turning mirror  936  redirects the laser pulse along a different linear optical axis to movable turning mirror  940 , which again redirects the laser pulse along a final optical axis to the target skin area cooled by the cooling window  920 . 
       FIG. 9F  is an optical schematic showing the optical path taken by infrared (IR) energy  920  emitted from a target skin area and traveling along a second optical path, and in particular the optical elements engaged by the IR energy in passing through the handpiece  900  to the temperature sensing element  950 . As previously noted, the second optical path is generally opposite to the direction of the first optical path, and is coaxial with the first optical path for at least a portion of the length of both paths. Because the target skin area is within the first skin area and in contact with cooling window  920 ,  FIG. 9F  shows IR energy  926  emitted from the skin directly through cooling window  920 . As noted in connection with  FIG. 9D , cooling window  920  is transmissive to the IR energy and is made of sapphire in the embodiment of  FIGS. 9A-9F . Passing through cooling window  920 , the IR energy  926  passes through plano-convex lens  944  and meniscus lens  942  and is then reflected by movable turning mirror (“scanning mirror”)  940 . The scanning mirror  940  may comprise any of a number of commercially available movable turning mirrors, such as a model MR-15-30 mirror available from Optotune Switzerland AG, Dietikon, Switzerland. In a given position, movable turning mirror  940  directs the laser pulses  908  to the target skin area (and not, e.g., adjacent tissue), and also reflects IR energy  926  emitted in the opposite direction from substantially only the target skin area. IR energy  926  reflected from scanning mirror  940  passes through plano-convex lens  938  before being reflected by turning mirror  936 . Convex lens  944 , meniscus lens  942 , movable turning mirror  940 , plano-convex lens  936 , and turning mirror  936  are as described in connection with  FIG. 9D , and for brevity further discussion is omitted here. 
     After reflection from turning mirror  936 , IR energy  926  is reflected by a first optical element comprising a concentric mirror  925  onto the temperature sensing element  950 . Concentric mirror  925  includes an open area (e.g., an aperture or slot) through which the laser pulses  908  pass without engaging the concentric mirror  925 . From cooling window  920  to concentric mirror  295 , the second optical path taken by IR energy  926  is generally opposite to—but coaxial with—the first optical path taken by laser pulses  908 . As noted, highly accurate temperature measurements are made possible by sensing IR energy  926  traveling opposite to but coaxial with the laser pulses  908 , because it enables the temperature sensing element  950  to sense IR energy from substantially only the target skin area (i.e., the same skin area receiving the laser pulse energy). However, it will be appreciated that the second optical path taken by the IR energy must eventually be diverted to a non-coaxial path from the first optical path to reach the temperature sensing element  950 , which cannot be located in the first optical path without blocking the laser pulses  908 . By including a concentric mirror  925  having an aperture, handpiece  900  allows the laser pulses  908  to pass through the concentric mirror but also allows IR energy  926  to travel along second optical path that is initially coaxial with first optical path until being reflected off-axis to the first optical path onto the temperature sensing element  950 . Temperature sensing element  950  may comprise any of a number of commercially available infrared sensors, such as a model P13243-013CA-SPL sensor available from Hamamatsu Corp., Bridgewater, N.J. In a preferred embodiment, temperature sensing element  950  includes an optical filter (e.g., a substrate transparent to the IR radiation from the target skin area with an optical coating) such that the temperature sensing element reflects the wavelength(s) of the laser source but transmits the IR energy radiated from the target skin area. 
       FIG. 9G  is the partially exploded view of the interior portion of handpiece  900  shown in  FIG. 9C , but includes added lines showing the path taken by IR energy  926  emitted from the target skin area to illustrate the second optical path traveled by the IR energy to the temperature sensing element  950 . Further discussion of the optical elements already noted in  FIG. 9C  is omitted.  FIG. 9G  depicts IR energy  926  emitted from the target skin area directly through the cooling window  905 , initially following a path having a linear optical axis from the target skin area to movable turning mirror  940 , which reflects the IR energy  926  along a different optical axis to turning mirror  936 . Turning mirror  936  again reflects the IR energy  926  along a different optical axis to the concentric mirror  925 , which reflects the IR energy onto the temperature sensing element  950 . A processor (not shown) processes the signal from temperature sensing element  950  to determine the surface skin temperature at a desire rate. The processor may be provided either as part of handpiece  950  or may be coupled by wire or wireless connection to temperature sensing element  950 . In preferred embodiments, temperature sensing element  950  and the processor associated with it are including in the housing  910 , while in alternate embodiments one or both may be located outside the housing or separate from handpiece  910 . 
     In some embodiments, a user interface  955  may provide an indicator to a user of one or more parameters of the system. This may include an indication of temperature (e.g., that a desired precooling or laser treatment temperature has been achieved, or that proper contact between the handpiece  950  and the skin of the patient has been achieved). 
       FIG. 10  discloses one embodiment of method  1000  of treating the skin of a patient with one or more therapeutic laser pulses according to the present disclosure. The method involves the use of one embodiment of a laser system as described in connection with  FIGS. 9A-9F . The method includes providing a laser source for generating one or more laser pulses as a laser therapy ( 1010 ). In one embodiment, the laser source comprises a semiconductor laser having a wavelength in one of the near-infrared spectrum and the short-wavelength IR spectrum. 
     The method also includes the step of providing a handpiece coupled to the laser source to receive at least one therapeutic laser pulse from the laser source, and to direct the pulses along a first optical path to a target skin area ( 1020 ). The handpiece includes a first optical element, at least one second optical element, and a contact cooling unit. The first optical element includes a first open area comprising one of an aperture and a slot through which the first optical path passes. In one embodiment, the first optical element may comprise concentric mirror  925  of  FIG. 9C . The at least one second optical element comprises one of a refracting element (e.g., a lens), and a reflective element (e.g., a mirror), and may include multiple lenses and mirrors similar to handpiece  900  in  FIG. 9C . The contact cooling unit comprises a cooling window for contacting and cooling a first skin area of the patient by direct contact. The first skin area includes a target skin area to be treated by the at least one therapeutic laser pulse (i.e., the target skin area is the skin that actually receives the energy of one or more therapeutic laser pulses). The cooling window is made of a thermally conductive material that is transmissive to infrared energy and laser light at a first wavelength range that includes the wavelength of the laser source. 
     Referring again to  FIG. 10 , the method includes the step of providing a temperature determination unit (TDU) to determine a surface temperature of the target skin area based on IR energy radiated from the target skin area through the cooling window ( 1030 ). The IR energy radiates along a second optical path that is shares a common optical axis with the first optical path for at least a portion of the first and second optical paths. The second optical path is preferably generally counterdirectional to the first optical path for at least a portion of the first and second optical paths, such that the IR energy for determining skin temperature propagates in the opposite direction to the direction of the laser pulse(s) for at least a portion of the second optical path. The TDU comprises a temperature sensing element that detects IR energy radiated through the cooling window along the second optical path, and a processor that determines the surface temperature of the target skin area based on the IR energy detected by the temperature sensing element. In one embodiment, the temperature sensing element may be the temperature sensing element  950  of  FIG. 9C , which provides a continuous or intermittent signal that is processed at a desired rate by the processor to determine the surface temperature of the target skin area at a desired rate (e.g., 10-1,000,000 times per second, or a sampling interval of from 100 msec or less). In some embodiments, the temperature determinations may comprise real-time temperature measurements used by a processor to control the duration of the laser therapy. 
     The method also includes the step of contacting the first skin area with the cooling window ( 1040 ). This may be done by a handpiece user (e.g., a physician or technician) bringing the cooling window into contact with a skin area to be treated, which cools the first skin area in contact with the cooling window from a first temperature to a second temperature ( 1045 ). The method further includes the step of generating, using the laser source, at least one therapeutic laser pulse having a wavelength with the first wavelength range ( 1050 ), and receiving the at least one therapeutic laser pulse with the handpiece ( 1055 ). The method also includes the step of applying the at least one therapeutic laser pulse to the target skin area by passing the pulse along the first optical path through the first open area of the first optical element, engaging the at least a second optical element, and through the cooling window into the target skin area ( 1060 ). 
     The method also includes determining the surface temperature of the target skin area one or more times before, during, or after the application of the at least one therapeutic laser pulse ( 1070 ). As part of this step, the temperature sensing element receives IR energy radiated from the target skin area along the second optical path, with the IR energy engaging the at least a second optical element and being reflected by the first optical element onto the temperature sensing element. The processor determines the surface temperature of the target skin area based on the infrared energy received by the temperature sensing element. 
     In some embodiments, the TDU may determine the surface temperature of the target skin area a plurality of times before, during, or after the application of the at least one therapeutic laser pulse. As a nonlimiting example, the TDU may initiate determining the surface temperature of the target skin area when the contact cooling window contacts the skin of the patient, and may determine the surface temperature of the target skin area once every millisecond as the skin is cooled, during the application of one or more therapeutic laser pulses to the target skin area, and after the termination of the pulses until the target skin area is cooled to a desired final temperature. In another nonlimiting example, the TDU may determine the temperature of the target skin area at least one time during the delivery of a therapeutic laser pulse, and at least one time before or after the pulse. In preferred embodiments, the temperature sensing element receives IR energy radiated substantially only from the target skin area, and the TDU determines the surface temperature based only on this IR energy. 
     Finally, the method includes performing at least one responsive action in response to determining the surface temperature of the target skin area ( 1080 ). The responsive action may include one or more actions selected from a list of responsive actions. These may include, e.g., terminating the application of the at least one therapeutic laser pulse to the target skin area (i.e., terminating a single pulse or a sequence of pulses), indicating (e.g., via a user interface or display) the instantaneous surface temperature of the target skin area, indicating a maximum surface temperature of the target skin area (e.g., displaying the maximum temperature reached during delivery of one or more pulses), changing at least one parameter of the laser therapy (e.g., reducing or increasing the intensity or duration of therapeutic laser pulses), and indicating when the surface temperature of the target skin area returns to a desired temperature following delivery of one or more therapeutic laser pulses to the target skin area. 
     In some embodiments, step of providing a handpiece includes providing a handpiece in which the at least a second optical element includes a mirror movable in at least two axes to direct the at least one therapeutic laser pulse to one or more desired target skin areas within the first skin area. The mirror may be the movable turning mirror  940  described in  FIG. 9C . In one embodiment, after one or more first therapeutic laser pulses are applied to a first target skin area with the mirror in a first position, the mirror may be moved to a second position, and the method may comprise delivering subsequent laser pulse(s) to a second target skin area different from the first target skin area, but still within the first target skin area cooled by the cooling window. In this case, the laser pulse(s) again pass along a first optical path through the first open area, engage the mirror in the second position, and pass through the cooling window to the second target skin areas. When the pulses are delivered to the second target skin area, the method may also comprise determining the temperature of the second target skin area one or more times before, during, or after the delivery of the laser pulse(s) to the second target skin area by receiving IR energy radiating from the second target skin area along the second optical path, engaging the mirror in the second position, and reflecting from the first optical element onto the temperature sensing element. As previously noted, the first and second optical axes are coaxial for at least a portion of the first and second optical paths. In a preferred embodiment, the first and second optical paths share a common optical axis for at least the portion of the first and second optical axes from the movable mirror to the cooling window. 
     In some embodiments, the step of providing a handpiece includes providing a handpiece in which the at least a second optical element includes a plurality of lenses and at least one mirror, and the first and second optical paths engage at least two of the plurality of lenses and the at least one mirror. In some embodiments, providing a handpiece in which the at least a second optical element includes at least four lenses and at least one mirror. 
     In some embodiments, the steps of generating at least one laser pulse, receiving the at least one pulse with the handpiece and applying it to the target skin area are repeated until the determined surface temperature of the target skin area reaches a target treatment temperature. In some embodiments, determining the surface temperature of the target skin area comprises repeatedly determining the target skin area a plurality of times during the application of a therapeutic laser pulse, and the method further comprises terminating the application of the laser pulse when the surface temperature of the target skin area reaches a target treatment temperature. 
     As noted in the discussion of  FIG. 6A , in some embodiments a contact sensing element or system may be provided to ensure good contact between the skin of the patient and the cooling window during treatment. In various embodiments, contact may be sensed by electrical contacts (e.g., electrodes capable of sensing changes in electrical conductivity or resistivity of the skin), or by detecting other skin parameters associated with contact such as force, pressure, vibration, temperature, sweat, etc. In two particular embodiments illustrated in  FIGS. 11A-11D and 12A-12B , the invention comprises systems and methods for laser treatment using a handpiece capable of sensing pressure or force on the external periphery of the cooling window. By sensing the pressure or force between the contact sensor and the skin, the system can determine when contact between the skin and cooling window is sufficient to enable effective treatment to be achieved. Poor contact may result in non-uniform cooling such that one or more target skin areas within the first skin area (i.e., the skin area in contact with the cooling window) are not cooled to a sufficiently low temperature to avoid pain, discomfort, or damage to overlying a target during laser pulse(s), especially for deeper target structures such as a sebaceous gland. Poor contact may involve a failure to fully contact the skin with the cooling window; failure to maintain even pressure of the cooling window across the first skin area; maintaining excessive pressure on the skin; or maintaining too little pressure. For example, if part of the cooling window is not in contact with the skin, or pressure is not evenly maintained, cooling may be uneven. Where cooling is uneven, some target skin areas may be overheated, while others may be underheated, resulting in poor efficacy. 
       FIG. 11A  shows one embodiment of a handpiece  1100  (which may be the handpiece of  FIGS. 9A-9F ) that includes a contact sensing unit  1150  for ensuring good contact between a cooling window  1120  and the skin during treatment. Handpiece  1100  includes similar structures to those in  FIGS. 9A-9F , including a housing  1110  having an optical aperture or port  1114  through which laser pulses exit the housing, and a contact cooling unit  1115  comprising the cooling window  1120 . The handpiece  1100  has a distal end  1104  at which the contact cooling unit  1115  and pressure sensor is located, and a proximal end  1102  coupled to an optical cable  1105  through which the laser pulses are delivered to the handpiece. Structures of handpiece  1100  that are also present in handpiece  900  of  FIGS. 9A-9F  will have similar functions, and further discussion is omitted here for brevity. 
     Cooling window  1120  has a generally planar and circular shape, and contact sensing unit  1150  includes a ring-shaped contact surface  1152  that is generally coplanar with cooling window  1120 . Contact surface  1152  may be part of a shroud  1154  that encloses sensing elements and/or electrical circuitry described in greater detail in connection with  FIG. 11B-11D . It will be appreciated that while the contact cooling window  1120  and contact surface  1152  are generally circular in the embodiment of  FIGS. 11A-D , other geometries (e.g., squares, ellipses, rectangles, etc.) could be used, including non-planar surfaces. Contact surface  1152  includes a plurality of protrusions  1155  that extend slightly from the plane of the contact area, and which each overlay a contact sensing element discussed more fully in connection with  FIGS. 11B-11D . 
       FIG. 11B  is a partially exploded view of the distal end  1104  of handpiece  1100 , showing additional details of the contact sensing unit  1150 . Handpiece  1100  is shown in unexploded form with contact cooling unit  1115 , including cooling window  1120  and heatsink  1116 , which includes a generally planar surface having a groove or recess  1167 , as shown in more detail in  FIG. 11D . Contact sensing unit  1150  includes a flexcircuit  1180  that includes a ring  1181  that fits in groove  1167  of heatsink  1116 , a ring  1160  having a plurality of pressure or force sensing regions  1161  capable of changing one or more electrical properties such as impedance, conductance, or resistance in response to an applied force or pressure, and a shroud  1154  that includes the contact surface  1152 . Flexcircuit  1180  is shown in greater detail in  FIG. 11C , and ring  1160  is discussed in greater detail in connection with  FIG. 11D . 
     Although depicted in  FIG. 11B  as integrally formed with shroud  1154 , in alternative embodiments, contact surface  1152 , may be provided as separate from but couplable to shroud  1154  (e.g., by slot-and-groove, screwed, or other connection). In the assembled handpiece ( FIG. 11A ), contact surface  1152  is generally coplanar with cooling window  1120 , and includes protrusions  1155  from the contact surface plane that are compressible or resiliently movable to generate a force and/or pressure on the pressure/force sensing regions  1161  of ring  1160 . In one embodiment, shroud  1154 , contact surface  1152 , and raised protrusions  1155  are preferably formed of a resilient polymer such as silicone rubber or another polymer that allows the protrusions  1155  to be compressed into contact with force sensing regions  1161  of ring  1160 , discussed in greater detail in  FIG. 11D . In an alternative embodiment, protrusions  1155  are pins or buttons biased outwardly via a spring located in groove  1167 , and which when pressed against the skin compress the springs, transferring the force to the force sensing regions  1161  of ring  1160 . In a further alternative embodiment, ring  1160  and ring  1181  of flexcircuit  1180  are located with an annular chamber within heatsink  1116 , and spring-biased pins or buttons in contact with each of the force-sensing regions  1161  of ring  1160  extend through small apertures in the heatsink  1116  and contact surface  1152 , replacing protrusions  1155 . This embodiment provides additional shielding of the ring  1160  and the pressure/force sensing regions  1161  thereof, as well as the flexcircuit, from contamination by moisture or debris. 
       FIG. 11C  provided additional details of flexcircuit  1180 , which includes a generally flexible body  1188  with circuit elements provided (e.g., by printing, soldering, etc.) thereon. Although the pressure sensing unit  1150  of  FIGS. 11A-11D  includes flexcircuit  1180  to provide electrical connections between pressure/force sensing regions  1161  of ring  1160  and a power source (not shown), it will be appreciated that other circuit coupling means (e.g., wires, wireless wi-fi connectivity, etc.) may be used instead of flexcircuit  1180 . At one end, the flexcircuit  1180  includes a ring  1181  having electrically conductive or pickup regions  1182 , each of which is electrically coupled to one of the pressure/force sensing regions  1161  of ring  1160  (e.g., by direct contact, soldering, etc.) as shown more clearly in  FIG. 11D . Ring  1181  also includes electrically inert areas  1184  that are not coupled to a pressure/force sensing region  1161  of ring  1160 . Electrical lines  1186  connect each pickup region  1182  to a connection pad  1190  for each of the pressure/force sensing regions  1161  of ring  1160 . A processor (not shown), preferably located in handpiece  1100 , provides an electrical signal through each pressure sensing element circuit, which comprises one of the electrical pads  1190 , its corresponding electrical line  1186 , and one of the pressure/force sensing regions  1161  of ring  1160 . The processor monitors changes in one or more electrical properties in the pressure/force sensing regions  1161  of ring  1160  (e.g., resistivity) as pressure is applied from a raised protrusion  1155  when contact is made between the protrusion  1155  and the skin of the patient. 
       FIG. 11D  is a cross-sectional view, indicated by section line  11 D of  FIG. 11A , of the details of each pressure sensing element associated with the protrusions  1155  extending from contact surface  1152 . Cooling window  1120  at the center of  FIG. 11D  is surrounded by heatsink  1116  acts as a frame for cooling window  1120  and includes a groove  1167 . In alternative embodiments (not shown) a cooling system may be omitted, and pulses may be delivered via an uncooled aperture that is surrounded by a frame other than heatsink  1116 . In still further embodiments, a frame or heatsink  1116  may only partially surround the cooling window  1120  Referring again to  FIG. 11D , ring  1181  of flexcircuit  1180 , and ring  1160  fit in groove  1167 . Although  FIG. 11A-11D  depicts a handpiece having six pressure sensing elements, in alternative embodiments any desired number of two or more elements (e.g., two, three, four, eight, or twelve) may be used. Flexcircuit  1180  is provided in the bottom of groove  1167 . Although the ring includes both electrically conductive regions  1182  and non-conductive regions  1184 , in the cross-section of  FIG. 11D , only the electrically conductive regions  1182  are shown. Ring  1160  is located immediately above electrically conductive regions  1182  and is maintained in direct contact therewith. Each pressure/force sensing region  1161  of ring  1160  comprises three separate structures. First, a pressure-responsive element  1162 , made of a material whose electrical properties (e.g., resistance) changes in a defined way with pressure or force, is maintained in direct contact with electrically conductive regions  1182  of flexcircuit  1180 . Any of a variety of materials having changing electrical characteristics in response to an applied force may be used. In one embodiment, the pressure-responsive element  1162  may comprise Velostat, a carbon-infused polymer available from Desco Industries, Sanford, NC. A cover element  1166  located above each pressure-responsive element  1162 , and a spacing element  1164  surrounding each pressure-responsive element, are provided for each pressure/force sensing region  1161  ( FIG. 11  B) of ring  1160 . Cover element  1166  and spacing element  1164  isolate the pressure-responsive element  1162  from extraneous forces and prevent the handpiece from indicating that skin contact has occurred except when a force is applied to the press-responsive element. For a given pressure/force sensing region  1161  of ring  1160 , when the handpiece  1100  contacts the skin of the patient, protrusions  1155  close the small gap separating the lower portion of the protrusion and the cover element  1166 , then transmit force from the skin to the pressure-responsive element  1162 . Each of the protrusions  1155  extends from contact surface  1152 , which is part of shroud  1154 . It will be appreciated that in alternative embodiments, separate structures may be provided for each of protrusions  1155 , contact surface  1152 , and shroud  1154 , although they are depicted in the embodiment of  FIGS. 11A-11D  as integrally formed. Together, protrusions  1155 , pressure/force sensing regions  1161 , and electrically conductive regions  1182  of flexcircuit  1180  function as a plurality of contact sensing elements coupled to heatsink  1116  or a different frame. 
     Contact sensing unit  1150  may determine one or more of force or pressure at each of the contact sensing elements (e.g., corresponding to protrusions  1155 ), and may calculate one or both of the force and the pressure between the skin and the handpiece  1100 . In one embodiment, the contact sensing unit may calculate forces as low as 0.1 newtons, although in preferred embodiments, the contact unit is capable of determining forces as low as 0.5 newtons. 
     Although not shown in  FIGS. 11A-11D , it will be appreciated that a laser source provides laser pulses to the handpiece  1100 . In alternative embodiments (not shown) a contact cooling unit may be omitted, and the handpiece may comprise a pulse delivery region to deliver the laser pulses through a pulse delivery aperture that does not comprise a contact cooling unit. 
     In preferred embodiments, a contact indicator, which may comprise a user interface similar to user interface  955  ( FIG. 9A ) may be provided. The contact indicator may provide one of a force feedback parameter and a pressure feedback parameter to a user. The feedback may indicate to a system user, based on force and/or pressure, one or more of the following feedback parameters: an indication of whether or not each of the plurality of contact sensing elements is in contact with the skin; an indication of one of the variation in pressure and the variation in force at each of the different locations of the contact sensing elements; an indication one of the variation in pressure and the variation in force between two or more of the contact sensing element locations; an indication that the pressure at each of the plurality of different locations exceeds a minimum pressure threshold; an indication that the pressure at each of the plurality of different locations is less than a maximum pressure threshold; an indication of the force at each of the different locations; an indication of the variation in force between two or more of the different locations; an indication that the force at each of the plurality of different locations exceeds a minimum pressure threshold; and an indication that the force at each of the plurality of different locations is less than a maximum pressure threshold. 
     I some embodiments, the system may also include a safety interlock preventing the laser source from generating the therapeutic laser pulse unless a desired force and/or pressure feedback parameter is provided by the contact indicator. In addition to the foregoing feedback parameters, the safety interlock may prevent the laser source from operating unless one of the following is provided: an indication that the pressure difference between the highest and lowest pressures among the different locations is less than a maximum pressure difference threshold, an indication that the difference between the highest and lowest applied forces among the different locations is less than a maximum force difference threshold; and an indication that desired cooling time has elapsed; and indication that a laser pulse has not exceeded a maximum pulse duration. 
       FIG. 12A  illustrates one embodiment of a handpiece  1200  (which may be the handpiece of  FIGS. 9A-9F ), in accordance to some embodiments herein. The handpiece  1200  may include both a contact sensing unit  1250  for ensuring sufficient contact between a cooling window  1220  and the skin during treatment and a force sensing unit  1251  to ensure adequate pressure. The handpiece  1200  includes similar structures to those in  FIGS. 9A-9F , including a housing  1210  (shown in partial cut away) having an optical aperture or port  1253  through which laser pulses exit the housing  1210 , and a contact cooling unit  1215  comprising the cooling window  1220 . The handpiece  1200  has a distal end  1204  at which the contact cooling unit  1215 , the contact sensing unit  1250 , and the force sensing unit  1251  are generally located. Like the handpiece  900 , the handpiece  1200  has a proximal end (not shown) coupled to an optical cable (not shown) through which the laser pulses are delivered to the handpiece  1200 . Structures of the handpiece  1200  that are also present in the handpiece  900  of  FIGS. 9A-9F  will have similar functions, and further discussion is omitted here for brevity. 
       FIG. 12B  is a partially exploded and partially cutaway view of the distal end  1204  of the handpiece  1200  and interrelated parts. The placement and interaction of the components of the handpiece  1200  may be more readily appreciated by simultaneous reference to  FIGS. 12A -! 2 B. The cooling window  1220  has a generally planar and circular shape, and contact sensing unit  1250  includes a ring-shaped contact surface  1256  that is generally coplanar with the cooling window  1220 . The contact surface  1256  may be part of a shroud (not shown). 
     It will be appreciated by those skilled in the art having benefit of the present disclosure, that while the contact cooling window  1220  and contact surface  1256  are generally circular in the embodiment of  FIGS. 12A-B , other geometries (e.g., squares, ellipses, rectangles, etc.) could be used, including non-planar surfaces. The contact surface  1256  includes a plurality of optical units  1255  that pass light from a plurality of optical transmitters/sensors  1257  through the optical units  1255  and onto the skin of the patient. Accordingly, light delivered from the optical transmitters/sensors  1257  reflects off the patient&#39;s skin and returns to the optical transmitters/sensors  1257 , which monitor the magnitude of the reflected light. Those skilled in the art will appreciate that the magnitude of the reflected light will increase to a maximum value as the contact surface  1256  and optical units  1255  come into contact with the surface of the patient&#39;s skin. 
     During treatment of a patient, uniform heating of the target skin area may be achieved by ensuring that the contact surface  1256  is coplanar with the target skin area. The use of a plurality of the optical transmitters/sensors  1257  enhances the positioning of the handpiece  1200  to achieve this coplanar relationship. In one embodiment, the controller  640  (see  FIGS. 6A and 6B ) receives information from the optical transmitters/sensors  1257  over electrical connectors  1258 . Under the control of software or hardware, the controller  640  compares the signals from each of the plurality of transmitters/sensors  1257  and interrupts or prevents the delivery of laser pulses when these signals are not substantially balanced. Those skilled in the art will appreciate that if, for example, the signals from two of the optical transmitters/sensors  1257  match, but the signal from the third optical transmitter/sensor  1257  is substantially less, then the handpiece  1200  is misaligned and not coplanar with the target skin area of the patient. This misalignment may lead to uneven heating of the target skin area. Accordingly, the controller  640  signals the operator that misalignment exists, prompting the operator to reposition the handpiece  1200 . In one embodiment, the handpiece  1200  includes visual and/or audio cues regarding misalignment, such as by energizing a green LED when coplanar alignment exists and/or energizing a red LED when coplanar alignment does not exist. 
     It will be appreciated that the problem of uneven heating of the target skin area based on variations from the coplanar orientation is exacerbated as the size of the target skin area increases. Relatively minor misalignment of the handpiece  1200  from the desired coplanar orientation can result in significant variations in the energy of the laser at various locations in the target skin area. The size of the target skin area can be significantly increased by applying the laser as a series of pulses dispersed over a preselected target area. For example,  FIG. 13  stylistically illustrates a target area  1300  that is generally circular in shape. In this embodiment the laser is aimed at a series of six targets  1310 - 1360  that roughly approximates the vertices of a hexagon and a seventh target  1370  at about the geometric center of the hexagon. This pattern distributes the energy of the laser pulses substantially evenly to achieve a substantially even distribution of the heat resulting from each laser pulse within the circular target area  1300 . In one embodiment, each laser pulse produces light having a diameter of about 3 mm with a spacing of about 0.5 mm, but can be varied, depending upon the physical characteristics of the patient&#39;s skin, such as by determining a Fitzpatrick score. In one embodiment, the series of seven laser pulses are each about 30 msec in duration with pauses of about 15 msec therebetween. 
     Returning to  FIGS. 12A and 12B , the force sensing unit  1251  is flexibly connected and spring biased to the distal end  1204  such that when the operator positions the handpiece  1200  in contact with the patient&#39;s skin and presses it thereagainst, movement occurs that is indicative of the pressure applied being of a sufficient magnitude to permit proper heating of the patient&#39;s target skin area via laser pulses. The force sensing unit  1251  includes an arm  1260  fixedly connected to the handpiece  1200  at a region  1261  by, for example, a plurality of bolts  1262 . A distal end  1263  of the arm  1260  is pivotally connected to the distal end  1204  of the handpiece  1200  via a conventional pin (not shown) extending through bore holes  1264 ,  1265 . A conical coil spring  1266  extends between the arm  1260  at region  1267  and the distal end  1204  of the handpiece  1200  at region  1246 . Thus, the spring  1266  urges the distal end  1204  of the handpiece  1200  to rotate counterclockwise, and a force applied to the contact surface  1256  urges the distal end  204  of the handpiece  1200  to rotate clockwise when the force applied to the contact surface  1256  exceeds the force of the conical spring  1266 . 
     A generally T-shaped bracket  1267  is affixed to the distal end  1204  of the handpiece  1200  at a region  1248  such that the T-shaped bracket  1267  moves with movement of the distal end  1204  of the handpiece  1200 . A two-piece position sensor  1268 ,  1269  is located between the T-shaped bracket  1267  and the optical aperture or port  1253 . It will be noted that movement of the distal end  1204  of the handpiece  1200  in a clockwise direction, such as by pressing the contact surface  1256  against the patient&#39;s skin, will separate the two-piece position sensor  1268 ,  1269  if the force exerted on the patient&#39;s skin is sufficient to overcome the force exerted by the conical spring  1266 . Separation of the components of the two-piece position sensor  1268 ,  1269  produces an electrical signal indicative of such a force being applied to the contact surface  256 , which is delivered to the controller  640  over an electrical conductor  1270 . 
     The controller  640  uses the signal from the force sensing unit  1251  over the conductor  1270  to interrupt or prevent the delivery of laser pulses when the force sensing unit  1251  indicates that the handpiece  1200  is not pressed against the patient&#39;s skin with sufficient force. Accordingly, the controller  640  signals the operator that the handpiece  1200  is not pressed sufficiently hard against the patient&#39;s skin, prompting the operator to press with additional force. In one embodiment, the handpiece  1200  includes visual and/or audio cues regarding sufficient force, such as by energizing a green LED when the force is adequate and/or energizing a red LED when the force is inadequate. 
     In preferred embodiments, a contact indicator and a force indicator, which may comprise a user interface similar to user interface  955  ( FIG. 9A ) may be provided. The contact indicator may provide one of a force feedback parameter and a pressure feedback parameter to a user. The feedback may indicate to a system user, based on force and/or pressure, one or more of the following feedback parameters: an indication of whether or not each of the plurality of contact sensing elements is in contact with the skin; an indication of pressure and force; an indication of the force. 
     In some embodiments, the system may also include a safety interlock preventing the laser source from generating the therapeutic laser pulse unless a desired indication is received from the force sensing unit  1251 , the contact sensing unit  1250 , or both. 
     In various embodiments, the present invention relates to the subject matter of the following numbered paragraphs. 
     101. A system for treating the skin of a patient with one or more therapeutic laser pulses, the system comprising: 
     a) a laser source adapted to generate at least one therapeutic laser pulse for application to a target skin area; 
     b) a handpiece optically coupled to the optical source to receive the at least one therapeutic laser pulse from the laser source and to direct the at least one therapeutic laser pulse to the target skin area along a first optical path, the handpiece comprising:
         1) a first optical element comprising a reflective element and having a first open area through which said first optical path passes, wherein the first open area comprises one of an aperture and a slot;   2) at least a second optical element comprising at least one of a refractive element and a reflective element, wherein the first optical path engages the at least a second optical element;   c) a temperature determination unit for determining a surface temperature of the target skin area based on infrared energy radiated from the target skin area through the cooling window along a second optical path sharing a common optical axis with the first optical path for at least a portion of the first and second optical paths, the temperature determination unit comprising:   1) a temperature sensing element for sensing infrared energy radiated through the cooling window along the second optical path, the temperature sensing element generating a first signal indicative of the infrared energy radiating along the second optical path, wherein the infrared energy radiating along the second optical path engages the at least a second optical element and is reflected by the first optical element to be detected by the temperature sensing element; and   2) a processor adapted to determine the surface temperature of the target skin area at one or more timepoints before, during, or after the application of one or more of therapeutic laser pulses based on the infrared energy detected by the temperature sensing element.       

     The particular embodiments disclosed and discussed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Embodiments of the present invention disclosed and claimed herein may be made and executed without undue experimentation with the benefit of the present disclosure. While the invention has been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to systems and apparatus described herein without departing from the concept and scope of the invention. Examples are all intended to be non-limiting. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention, which are limited only by the scope of the claims.