DYNAMIC CORRECTION FOR AN ACOUSTO-OPTIC DEFLECTOR

An optical scanner may include a sampler to receive an optical beam and provide a sampled beam including a portion of the optical beam, a dispersive element to spectrally disperse the sampled beam along a dispersion direction, one or more detectors to receive at least a portion of the sampled beam dispersed along the dispersion direction, one or more acousto-optic deflectors (AODs) configured to deflect the optical beam from the sampler, and a controller. The controller may determine a center of mass of the sampled beam dispersed along the dispersion direction based on signals from at least one of the one or more detectors, and generate a drive signal for at least one of the one or more AODs to deflect the optical beam from the sampler along a selected deflection angle based on the center of mass.

TECHNICAL FIELD

The present disclosure is directed generally to an optical beam scanner and, more particularly, to dynamic corrections for an optical beam scanner in the presence of spectral variations of a scanned beam.

BACKGROUND

Acousto-optic deflectors (AODs) may be used as optical beam scanning devices in a wide range of applications. AODs beneficially provide relatively fast scanning speeds but are sensitive to spectral variations of an optical beam being scanned. It may therefore be desirable to develop systems and methods to cure the above deficiencies.

SUMMARY

An optical scanner is disclosed in accordance with one or more illustrative embodiments of the present disclosure. In one illustrative embodiment, the optical scanner includes a sampler to receive an optical beam and provide a sampled beam including a portion of the optical beam. In another illustrative embodiment, the optical scanner includes a dispersive element to spectrally disperse the sampled beam along a dispersion direction. In another illustrative embodiment, the optical scanner includes one or more detectors to receive at least a portion of the sampled beam dispersed along the dispersion direction. In another illustrative embodiment, the optical scanner includes one or more acousto-optic deflectors (AODs) to deflect the optical beam from the sampler. In another illustrative embodiment, the optical scanner includes a controller. In another illustrative embodiment, the controller determines a center of mass of the sampled beam dispersed along the dispersion direction based on signals from at least one of the one or more detectors. In another illustrative embodiment, the controller generates a drive signal for at least one of the one or more AODs to deflect the optical beam from the sampler along a selected deflection angle based on the center of mass.

A system is disclosed in accordance with one or more illustrative embodiments of the present disclosure. In one illustrative embodiment, the system includes an optical source configured to generate an optical beam. In another illustrative embodiment, the system includes a scanner. In another illustrative embodiment, the scanner includes a sampler to receive the optical beam and provide a sampled beam including a portion of the optical beam, a dispersive element to spectrally disperse the sampled beam along a dispersion direction, one or more detectors to receive at least a portion of the sampled beam dispersed along the dispersion direction, and one or more acousto-optic deflectors (AODs) to deflect the optical beam from the sampler. In another illustrative embodiment, the system includes a controller. In another illustrative embodiment, the controller determines a center of mass of the sampled beam dispersed along the dispersion direction based on signals from at least one of the one or more detectors. In another illustrative embodiment, the controller generates a drive signal for at least one of the one or more AODs to deflect the optical beam from the sampler along a selected deflection angle based on the center of mass. In another illustrative embodiment, the system includes one or more focusing optics configured focus the optical beam deflected by the one or more AODs to a sample.

A method is disclosed in accordance with one or more illustrative embodiments of the present disclosure. In one illustrative embodiment, the method includes generating a sampled beam from a received optical beam, where the sampled beam includes a portion of the optical beam. In another illustrative embodiment, the method includes spectrally dispersing the sampled beam along a dispersion direction. In another illustrative embodiment, the method includes detecting, with one or more detectors, at least a portion of the sampled beam dispersed along the dispersion direction. In another illustrative embodiment, the method includes determining a center of mass of the sampled beam dispersed along the dispersion direction based on signals from at least one of the one or more detectors. In another illustrative embodiment, the method includes generating a drive signal for an acousto-optic deflector (AOD) to deflect the optical beam along a selected deflection angle based on the center of mass. In another illustrative embodiment, the method includes deflecting the optical beam with the AOD driven by the drive signal.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to systems and methods for dynamic control of an optical scanner to compensate for spectral variations of an optical beam (e.g., a laser beam, or the like).

In some embodiments, an optical scanner includes at least one acousto-optic deflector (AOD) to receive and redirect an optical beam (e.g., scan an optical beam), one or more detectors to monitor spectral variations of the optical beam, and a controller to provide a drive signal to the AOD that dynamically adjusts to compensate for spectral variations of the optical beam measurable by at least one of the one or more detectors.

An AOD may include one or more transducers to generate acoustic waves in a host material, where driving the transducers with a periodic drive signal may form a diffraction grating in the host material. In this way, an incident optical beam may be redirected via diffraction, where a deflection angle of the optical beam from the AOD (e.g., a diffraction angle from the diffraction grating) may be controlled based on a frequency of the drive signal and an intensity of the optical beam from the AOD may be controlled based on an amplitude of the drive signal.

It is contemplated herein that such an AOD may beneficially provide higher scanning speeds than mechanical scanners (e.g., galvo mirrors, rotating polygons, or the like), but may be highly sensitive to spectral variations of an optical beam being scanned. In particular, spectral variations of the optical beam may result in variations of a diffraction angle of the optical beam by the AOD and thus variations in the deflection angle of the optical beam. However, the systems and methods disclosed herein may allow for dynamic compensation of spectral variations to provide fast and accurate optical scanning with an AOD despite spectral variations.

Additional embodiments of the present disclosure are directed to systems and methods for dynamically compensating for power fluctuations of the optical beam when using wavelength-sensitive polarization optics. Some polarization optics may provide non-uniform performance (e.g., transmissivity and/or reflectivity) for different wavelengths. In this case, spectral variations of the optical beam may result in power fluctuations when such wavelength-sensitive polarization optics are used in an optical scanner. In some embodiments, the controller may further dynamically adjust an amplitude of a drive signal to an AOD to adjust a power of the optical beam exiting the AOD and thus compensate for power fluctuations associated with interaction with wavelength-sensitive polarization optics. Such wavelength-sensitive polarization optics may be placed before or after the AOD.

Additional embodiments of the present disclosure are directed to systems and methods for dynamically compensating for beam size variations of an optical beam. For example, beam size and positioning accuracy of an optical beam may be directly affected when the power distribution of the optical beam dynamically changes between different spectral bands. Further, it may be the case that spectral variations of the optical beam are associated with operation of an associated optical source (e.g., a laser source) in different optical modes, where each optical mode may also provide different beam characteristics (e.g., beam size, beam divergence, or the like). In this way, switching between these different modes (e.g., mode hopping) and/or simultaneous lasing of different modes may result in any combination of spectral variations and/or variations in beam characteristics. In some embodiments, an optical scanner includes one or more detectors to monitor a beam size of an optical beam and one or more adaptive optics (e.g., a deformable mirror, a micro-electro-mechanical system (MEMS) device, a phase modulator, or the like), where the controller dynamically generates drive signals for the adaptive optics to compensate for variations of the beam size.

Referring now toFIGS.1A-6, systems and methods for optical scanning in the presence of spectral variations and/or beam size variations are described in greater detail, in accordance with one or more embodiments of the present disclosure.

FIG.1Ais a block diagram of an optical scanner100, in accordance with one or more embodiments of the present disclosure.FIG.1Bis a block diagram of a system102including an optical scanner100, in accordance with one or more embodiments of the present disclosure.

In some embodiments, the optical scanner100includes an optical source104to generate an optical beam106and at least one AOD108to control a deflection angle of the optical beam106. The optical scanner100may further include a controller110with one or more processors112configured to execute a set of program instructions maintained in memory114(e.g., a memory device), where the controller110may generate at least one drive signal116for the AOD108. In this way, the controller110may direct or otherwise control the AOD108to direct the optical beam106along a particular deflection angle, scan pattern, or the like based on the drive signal116. As is described in greater detail below, the controller110may further adjust one or more aspects of the drive signal116to compensate for spectral variations of the optical beam106and provide a consistent deflection angle of the optical beam106by the AOD108. For example, the optical scanner100may monitor spectral variations of the optical beam106by sampling a portion of the optical beam106with a sampler118to form a sampled beam120, spectrally dispersing the sampled beam120with a dispersive element122, and collecting at least a portion of the spectrally-dispersed sampled beam120with one or more detectors124coupled to the controller110.

Additionally, although not explicitly shown inFIG.1A, the optical scanner100may generally include any number of AODs108. For example, the optical scanner100may include multiple AODs108arranged to provide scanning of the optical beam106along multiple directions (e.g., orthogonal directions). In the case of multiple AODs108, the controller110may adjust one or more aspects of the drive signal116associated with each AOD108to compensate for spectral variations of the optical beam106and provide a consistent deflection angle of the optical beam106by each AOD108. In this way, any description of the operation or correction of an AOD108herein may be extended to apply to multiple AODs108.

The one or more processors112of a controller110may include any processor or processing element known in the art. In this sense, the one or more processors112may include any microprocessor-type device configured to execute algorithms and/or instructions. For the purposes of the present disclosure, the term “processor” or “processing element” may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more micro-processor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors112may include any device configured to execute algorithms and/or instructions (e.g., program instructions stored in memory). In some embodiments, the one or more processors112may be embodied as a desktop computer, mainframe computer system, workstation, image computer, parallel processor, networked computer, or any other computer system configured to execute a program configured to operate or operate in conjunction with the optical scanner100, as described throughout the present disclosure. Moreover, different subsystems of the optical scanner100may include a processor or logic elements suitable for carrying out at least a portion of the steps described in the present disclosure. Therefore, the above description should not be interpreted as a limitation on the embodiments of the present disclosure but merely as an illustration. Further, the steps described throughout the present disclosure may be carried out by a single controller or, alternatively, multiple controllers. Additionally, the controller110may include one or more controllers housed in a common housing or within multiple housings. In this way, any controller or combination of controllers may be separately packaged as a module suitable for integration into the optical scanner100.

The memory114may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors112. For example, the memory114may include a non-transitory memory medium. By way of another example, the memory114may include, but is not limited to, a read-only memory (ROM), a random-access memory (RAM), a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid-state drive and the like. It is further noted that the memory114may be housed in a common controller housing with the one or more processors112. In some embodiments, the memory114may be located remotely with respect to the physical location of the one or more processors112and the controller110. For instance, the one or more processors112of the controller110may access a remote memory (e.g., server), accessible through a network (e.g., internet, intranet and the like).

As another example, the controller110may include or be coupled with one or more encoders (e.g., optical encoders), which may be used for any suitable purposes including, but not limited to, monitoring a position of the optical beam along one or more scan axes and providing associated feedback for control.

The optical scanner100may be integrated into any suitable system for dynamic beam control. As an illustration,FIG.1Bdepicts the use of the optical scanner100in a system102suitable for materials processing. In some embodiments, the system102includes a stage126to secure a sample128. In some embodiments, the system102includes one or more focusing optics130to focus the optical beam106from the optical scanner100onto the sample128. Accordingly, the system102may direct or scan an optical beam106across the sample128in any pattern, where the AOD108within the optical scanner100is adjusted to compensate for spectral variations of the optical beam106such that the position of the optical beam106on the sample128may be consistent despite the spectral variations.

The focusing optics130may include any number or type of focusing optics suitable for focusing the optical beam106onto the sample128. In some embodiments, the focusing optics130include an F-theta lens to provide consistent focusing of the optical beam106across a flat plane and linear displacement across the sample128as a function of input angle (e.g., associated with the deflection angle of the optical beam106from the optical scanner100).

In some embodiments, the system102includes one or more additional components to provide additional control over the position of the optical beam106on the sample128. For example, the stage126may include a translation stage with one or more linear or angular actuators to adjust a position of the sample128along any number of degrees of freedom. As another example, the system102may include an additional deflector132such as, but not limited to, a galvo mirror as depicted inFIG.1B, a rotating polygon, or an additional AOD. In this way, the scanning range may be increased beyond the range of the optical scanner100. For instance, mechanical beam scanners such as the stage126or the galvo mirror depicted inFIG.1Bmay provide a larger scanning range than the optical scanner100but with relatively slower scan rates.

The system102may further include any number of additional optics to control various aspects of the optical beam106such as, but not limited to, optical relays, beam expanders, polarizers, spectral filters, spatial filters, or apodizers. Although not explicitly illustrated, such additional optics may be distributed at any suitable locations throughout the system102and/or within the optical scanner100.

In some embodiments, the system102and/or the optical scanner100further includes an adaptive optical element134providing spatially-resolved control over portions of the optical beam106. In this way, properties such as, but not limited to, beam size, beam divergence, or focal properties of the optical beam106deflected by the AOD108may be adjusted to provide consistent performance despite variations of the optical beam106. For example, the adaptive optical element134may be used within the system102to provide a consistent focused spot size on the sample128despite variations of the optical beam106.

Referring now generally toFIG.1A, various aspects of the optical scanner100are described in greater detail, in accordance with one or more embodiments of the present disclosure.

The optical beam106may include one or more selected wavelengths of light including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation. Further, the optical beam106from the optical source104may have any temporal profile including, but not limited to, a continuous-wave (CW) profile, a pulsed profile, or a modulated profile.

The optical source104may generally include any type of illumination source suitable for providing at least one optical beam106including, but not limited to, a laser source or a light emitting diode (LED). It is noted that the optical source104may be integrated within the optical scanner100, the system102, or as an external component. In some embodiments, the optical source104includes a narrowband laser source providing light centered around a center wavelength. It is contemplated herein that the smaller a bandwidth of the optical beam106, the less spatial dispersion will be induced by a dispersive element such as, but not limited to, an AOD108.

In some embodiments, the optical source104is a carbon dioxide (CO2) laser source. For example, a CO2laser may provide an optical beam106having a wavelength in a range of 9-12 nanometers, though this is indented to be illustrative rather than limiting.

The AOD108may include any type of deflector known in the art suitable for controlling a deflection angle of the optical beam106through diffraction by acoustic waves in a material.FIG.2is a simplified schematic of an AOD108, in accordance with one or more embodiments of the present disclosure.

In some embodiments, the AOD108includes at least one transducer202coupled to a host material204. The host material204may include any type of material suitable for interaction with the optical beam106such as, but not limited to, a glass or a crystal. For example, the host material204may be transparent to the optical beam106. As an illustration, the host material204may have an absorptivity for wavelengths associated with the optical beam106below a selected threshold and/or may have a transmissivity for wavelengths associated with the optical beam106above a selected threshold.

A transducer202may be any component suitable for generating acoustic waves in the host material204. In some embodiments, A transducer202is a piezoelectric material that may expand or contract in response to an applied voltage (e.g., a drive signal116), which may generate an acoustic wave in the host material204.

In some embodiments, the AOD108(e.g., one or more transducers in an AOD108) is driven by a periodic drive signal116to generate a periodic distribution of acoustic waves in the host material204, which may operate as a diffraction grating206suitable for diffracting the optical beam106. In particular, the periodic distribution of acoustic waves may provide a periodic distribution of refractive index in the host material204that operates as a diffraction grating206.

Diffraction of the optical beam106by the diffraction grating206may generally result in any number of diffraction orders (e.g., zero-order diffraction208, first-order diffraction210, second-order diffraction212, or the like). In this configuration, any of the diffraction orders may be utilized as a deflected optical beam106. In some embodiments, the AOD108is configured such that the optical beam106interacts with the diffraction grating206at or near the Bragg angle such that a substantial portion of the energy in the optical beam106is diffracted as first-order diffraction210(e.g., +1 order diffraction or −1 order diffraction). Accordingly, the first-order diffraction210may represent a deflected optical beam106and a deflection angle214of the optical beam106from the AOD108may correspond to the first-order diffraction angle216.

Diffraction of the optical beam106by the diffraction grating206in the AOD108may generally be governed by the grating equation:

where d is the period of the diffraction grating206, m is the diffraction order, λ is the wavelength of the optical beam106, θiis the incidence angle of the optical beam106, and θmis the diffraction angle of the associated diffraction order of the optical beam106. The first-order diffraction angle216is thus

and varies based on the wavelength (λ) of the optical beam106as well as the period (d) of the diffraction grating206. More generally, Equation (1) illustrates that non-zero diffraction orders including, but not limited to, first-order diffraction210are spectrally dispersed such that the angle of diffraction θmvaries based on the wavelength (λ) of the optical beam106.

The power of the first-order diffraction210and thus the efficiency of the AOD108for deflecting the optical beam106may depend on various factors including, but not limited to, the magnitude of the variation of refractive index of the host material204(Δn, where n is the refractive index of the host material204) associated with the diffraction grating206, which may be referred to as the modulation depth of the diffraction grating206. In an AOD108, this modulation depth (Δn) may be based on an amplitude of an acoustic wave generated by the transducer202.

For a given wavelength (λ) of the optical beam106, the first-order diffraction angle216and thus the deflection angle214of the optical beam106from the AOD108may be varied within a scan range (e.g., a walking window) by adjusting a frequency of the drive signal116. The period (d) of the diffraction grating206may be inversely related to the frequency of the drive signal116. For example, the controller110may generate the drive signal116and may adjust the frequency of the drive signal116in any selected pattern to adjust the deflection angle214in any selected pattern.

It is contemplated herein that the optical source104may exhibit various instabilities such as, but not limited to, instabilities in the spectrum or the beam size of the optical beam106. In the case of a laser source, such instabilities may be, but are not required to be, associated with mode hopping between different supported modes, each of which may have a different wavelength (e.g., central wavelength).

Spectral variations of the optical beam106(e.g., associated with such instabilities of the optical source104or more generally associated with any mechanism) may induce errors of the deflection angle of the optical beam106. Considering the illustration inFIG.2as a non-limiting example, spectral variations of the optical beam106may affect the first-order diffraction angle216and thus the deflection angle214of the optical beam106from the AOD108based on Equations (1) and (2). As a result, a shift of the wavelength (λ) of the optical beam106from an expected value (e.g., due to a spectral variation) may result in an error of the deflection angle214from the AOD108.

While it may be possible to avoid such deflection angle errors by either using a wavelength insensitive scanning technique (e.g., a mechanical technique such as, but not limited to, galvo mirrors or rotating polygons) or selecting an optical source104having reduced spectral variations, such approaches are not always desirable. For example, mechanical beam scanning techniques may generally have slower positioning rates (e.g., scan rates) and may thus limit the throughput of a system. As another example, techniques providing an optical beam106with high spectral stability may limit the achievable power of the optical beam106. Put another way, mode hopping (and the associated spectral instability) may be a consequence of high-power operation of some laser sources such as, but not limited to CO2laser sources.

Accordingly, it may be desirable in some applications to utilize an optical scanner100including an AOD108in combination with an optical source104exhibiting spectral variations. In this way, the optical source104may be selected to provide an optical beam106with a selected power without regard to spectral instabilities and without sacrificing scanning speed or precision.

Referring again toFIGS.1A-1B, in some embodiments, the optical scanner100includes various components to compensate for spectral variations of the optical beam106.

In some embodiments, the optical scanner100includes a sampler118to generate a sampled beam120from the optical beam106, a dispersive element122to spectrally disperse the sampled beam120, and one or more detectors124to capture at least a portion of the spectrally-dispersed sampled beam120. In this way, the one or more detectors124may generate signals indicative of the spectral variations of the sampled beam120and thus the spectral variations of the optical beam106. The controller110may then adjust the drive signal116of the AOD108to compensate for the spectral variations of the optical beam106over time to provide an accurate deflection angle214of the optical beam106despite the spectral variations.

The sampler118may include any optical component known in the art suitable for extracting a portion of the optical beam106as a sampled beam120. For example, the sampler118may include, but is not limited to, an optical wedge or a beamsplitter. As another example, the sampler118may include a mirror providing less than 100% reflectance, where a portion of the optical beam106propagates through the mirror and is utilized as the sampled beam120.

The dispersive element122may include any optical element known in the art suitable for spatially dispersing the sampled beam120such as, but not limited to, a diffraction grating or a prism. In this way, the dispersive element122(and the detector124) may be an in-line or real-time spectrometer. For example, in the case of a diffraction grating, the dispersive element122may generate multiple diffraction orders based on Equation (1), where non-zero diffraction orders are spectrally dispersed. In some embodiments, as described with respect to the diffraction grating206of the AOD108, the dispersive element122is arranged to satisfy the Bragg condition such that a substantial portion of the power of the sampled beam120is diffracted as first-order diffraction.

The dispersive element122may generally have any dispersion value. In some embodiments, the dispersive element122has sufficient dispersion to enable the detection of spectral variations of the sampled beam120by at least one of the one or more detectors124. As an illustration, the dispersive element122may include, but is not required to include, a diffraction grating with a ruling of 150 lines per millimeter to provide sufficient dispersion to enable the detection of spectral variations of the sampled beam120by at least one of the one or more detectors124.

FIG.3is a plot of a spatially dispersed sampled beam120, in accordance with one or more embodiments of the present disclosure. In particular,FIG.3corresponds to a plot of a spatially dispersed sampled beam120associated with a CO2laser and depicts light dispersed along a dispersion direction302.

Spectral variations of an optical beam106may manifest in multiple ways and may depend on the particular optical source104. In some embodiments, the optical beam106may include power centered around a single wavelength (e.g., a single central wavelength), where this wavelength may shift over time. For example, such behavior may be associated with, but is not limited to, thermal variations in the optical source104. In some embodiments, as depicted inFIG.3, an optical source104may generate an optical beam106having power centered around one or more wavelengths associated with one or more optical modes. In this way, any number of optical modes (and associated wavelengths) may be present at any particular time and the distribution of wavelengths may change over time (e.g., due to mode hopping)

The one or more detectors124may include any type of detector known in the art suitable for detecting spectral variations of the sampled beam120when coupled with the dispersive element122. In some embodiments, a detector124is formed as a multi-pixel detector, where at least two of the pixels are distributed along the dispersion direction302provided by the dispersive element122. In this way, different pixels of the detector124along the dispersion direction302may capture different wavelengths or wavelength ranges of the sampled beam120.

Lateral shifts of light along the dispersion direction302as measured by a detector124may be calibrated to wavelength shifts of the sampled beam120based on the value of the dispersion provided by the dispersive element122and a separation distance between the dispersive element122and the detector124. For example, the value of the dispersion provided by the dispersive element122may be characterized as Δθ/Δλ, where Δθ is an angular shift of the deflection angle214associated with a wavelength shift of Δλ. This may then be mapped to a linear shift Δl on the detector124.

The controller110may then provide a drive signal116to the AOD108using any technique suitable for compensating for spectral variations of the optical beam106(e.g., as measured on the sampled beam120). In some embodiments, the controller110determines a center of mass (COM) of the spectrally dispersed sampled beam120and dynamically adjusts a frequency of a drive signal116to the AOD108based on the COM of the spectrally dispersed sampled beam120.

As an illustration, the controller110may calculate a first frequency (f0) of a drive signal116. This first frequency may be selected to provide a desired deflection angle214for the optical beam106based on an expected wavelength (λ0) of the sampled beam120and thus based on an expected COM (COM0) of the spectrally-dispersed sampled beam120as measured by a detector124.

The expected COM (COM0) of the spectrally-dispersed sampled beam120may correspond to any value and may correspond to a center position on the detector124. For example, if a spectrum of the optical beam106(and thus the sampled beam120) varies within a known spectral range, the associated COM of the spectrally-dispersed sampled beam120may vary within a known range of positions on a plane of the detector124. The detector124may then be placed at any suitable location to capture this known range of positions. In some embodiments, a center of the detector124is placed in a center of this known range of positions.

The controller110may receive signals from the detector124indicating the COM of the spectrally-dispersed sampled beam120. The controller110may then determine an adjustment frequency (Δf) required to compensate for shifts of the COM of the spectrally-dispersed sampled beam120from the expected value (ΔCOM).

The controller110may then provide a drive signal116to the AOD108with a second frequency (f2) corresponding to the first frequency (f1) plus or minus an adjustment frequency (Δf) based on any measured deviation of the COM of the spectrally-dispersed sampled beam120from the expected value (ΔCOM).

It is contemplated herein adjusting a frequency of the drive signal116based on deviations of a COM of the spectrally-dispersed sampled beam120may provide a robust and efficient technique suitable for compensating for a wide variety of spectral variations. However, a detector124placed after the dispersive element122need not necessarily resolve spectral power in each optical mode or at each particular wavelength of the sampled beam120. Rather, a COM of the spectrally-dispersed sampled beam120may provide an indicator of spectral variation in a manner relevant to compensation of the impact of spectral variation on the deflection angle214.

For example, in the case that the spectrum of the sampled beam120(and thus the optical beam106) includes power centered around a single center wavelength that shifts over time, the COM of the sampled beam120may correspond to this center wavelength such that the frequency of the drive signal116(f2) may be adjusted to track this center wavelength.

As another example, in the case that the spectrum of the sampled beam120is more complex and includes power at multiple wavelengths that shift over time, the COM of the sampled beam120may correspond to an effective central wavelength of spectral power distribution. In some cases, the sampled beam120may not have any power at this effective central wavelength. However, adjusting the deflection angle214of the optical beam106based on this effective central wavelength may provide accurate optical scanning based on the effective center wavelength of the spectral power distribution.

As an illustration,FIGS.4A-4Cdepict a variation of the COM of a sampled beam120in response to various spectral variations, in accordance with one or more embodiments of the present disclosure.FIG.4Ais a simplified conceptual schematic of a first spectrally-dispersed sampled beam120including a single lobe402associated with a first wavelength (λ0), in accordance with one or more embodiments of the present disclosure.FIG.4Bis a simplified conceptual schematic of a second spectrally-dispersed sampled beam120including a single lobe404associated with a second wavelength (λ1), in accordance with one or more embodiments of the present disclosure.FIG.4Cis a simplified conceptual schematic of a third spectrally-dispersed sampled beam120including a first lobe406associated with a third wavelength (λ2) and a second lobe408associated with a fourth wavelength (λ3), in accordance with one or more embodiments of the present disclosure.

InFIGS.4A-4C, the lobes402-408each have a symmetric power distribution (not illustrated) and the same physical size. InFIGS.4A and4B, the lobes402,404each contain the full power of the sampled beam120. InFIG.4C, the power of the sampled beam120is evenly distributed between the lobes406,408.

InFIG.4A, the COM of the sampled beam120may correspond to a center of the lobe402. Further, the center of the lobe402may correspond to a physical center of the detector124, which may correspond to an expected COM position (COM0). In this situation,FIG.4Amay correspond to a case in which no compensation to the frequency of the drive signal116is needed.

InFIG.4B, the COM of the spectrally-distributed sampled beam120may correspond to a center of the lobe404. This situation may correspond to a simple shift of the center wavelength of the sampled beam120to λ1relative to λ0and a corresponding COM shift (ΔCOM) of the spectrally-distributed sampled beam120. Accordingly, the controller110may provide a frequency adjustment (Of) to compensate for the COM shift (ΔCOM).

InFIG.4C, the COM of the spectrally-distributed sampled beam120may correspond to an additional wavelength λ4, where the sampled beam120may or may not provide light at this wavelength. For example,FIG.4Cillustrates two lobes at wavelengths λ2and λ3, where the COM corresponds to the additional wavelength λ4located between the two lobes. In any case, this wavelength λ4may correspond to a COM of the spectral power distribution of the sampled beam120and may thus provide a convenient wavelength to use as a basis for adjusting the frequency of the drive signal116for deflecting the optical beam106. Although various portions of the optical beam106may have different deflection angles214, a COM associated with the power of the optical beam106may be associated with this additional wavelength λ4.

Referring generally toFIGS.4A-4C, it is to be understood thatFIGS.4A-4Cand the associated descriptions are provided merely for illustrative purposes and should not be interpreted as limiting. Rather, the spectrally-distributed sampled beam120may have any distribution across the detector124.

Referring again toFIG.1A, the optical scanner100may include any type of detector124suitable for determining a COM of the spectrally-distributed sampled beam120.

In some embodiments, a detector124includes a multi-pixel sensor array such as, but not limited to, a line sensor for 1D measurements or an area sensor for 2D measurements. For example, the detector124may be formed as, but is not limited to, a complementary metal-oxide-semiconductor (CMOS) sensor, a charge-coupled device (CCD), or an array of single-pixel photodiodes. The COM of the spectrally-distributed sampled beam120may be determined using any suitable technique. For instance, each pixel may correspond to a range of wavelengths of the sampled beam120such that the COM may be determined based on the signal amplitudes of the various pixels.

In some embodiments, a detector124includes a position-sensitive sensor such as, but not limited to a segmented sensor or a lateral effect photodiode. For example, a segmented sensor may include one or more pixels in each of two or more segments. In this way, the COM of the incident light may be determined by relative ratios of signals in each segment. As an illustration, a segmented sensor with two segments distributed along the dispersion direction302may provide a one-directional measurement of the COM along the dispersion direction302. As another illustration, a segmented sensor with four segments arranged as quadrants may provide a two-directional measurement and may be suitable for, but is not limited to, accounting for misalignments between the detector124and the dispersive element122. By way of another example, a lateral effect photodiode may include a single extended photodiode element with multiple contacts, where a COM of incident light may be determined based on relative signals from the multiple contacts.

It is contemplated herein that a position-sensitive sensor may typically provide a faster readout time than a multi-pixel sensor array due to a relatively smaller number of pixels and/or readout efficiencies. As a result, a position-sensitive sensor may enable relatively faster sampling rates of the sampled beam120and thus enable relatively faster corrections to the frequency of the drive signal116than a multi-pixel sensor array. However, a multi-pixel sensor array may provide a more precise measurement of the spectral distribution of the sampled beam120than a position-sensitive sensor. Accordingly, the optical scanner100may include any combination of position-sensitive sensors or multi-pixel sensor arrays.

It is further contemplated herein that a 1D measurement may be sufficient to provide compensation of multiple AODs108along multiple scan axes. 2D measurements may be suitable for a configuration in which the optical beam106is sampled after the AODs108and frequency corrections are done in a closed loop to return the COM to the 2D center on an imaged plane of the AOD108plane (e.g., after a beam sampler and an optical relay).

In some embodiments, the optical scanner100and/or the system102includes an adaptive optical element134providing spatially-adjustable control of different portions of the optical beam106. For example, the adaptive optical element134may include, but are not limited to, a deformable mirror, a MEMS device, a spatial light modulator (SLM), or a piezoelectric mirror (or mirror pair). The adaptive optical element134may be suitable for controlling any beam parameter such as, but not limited to, a beam size, a beam divergence, or a beam propagation direction.

The optical scanner100may include adaptive optical element134at any suitable location. For example, as illustrated inFIGS.1A-1B, adaptive optical element134may be located in a path of the optical beam106after the AOD108to modify one or more properties of the optical beam106after deflection by the AOD108. Further, the adaptive optical element134may be communicatively coupled with the controller110such that the controller110may provide a drive signal136to the adaptive optical element134to control one or more aspects of the adaptive optical element134. As an illustration, the controller110may adjust the drive signal136for the adaptive optical element134based on signals from any of the one or more detectors124.

In some embodiments, the adaptive optical element134provide an adjustable optical power. For example, the adaptive optical element134may operate as a lens with an adjustable focal length. In this way, the adaptive optical element134may provide an adjustable optical power based on a spectrum of the optical beam106(e.g., as measured by the sampled beam120). Further, the adaptive optical element134may provide a different optical power along two directions (e.g., along two scanning direction). In this way, the adaptive optical element134may operate as a cylindrical focusing element.

It is contemplated herein that various instabilities of the optical beam106may result in variations of a spot size and/or divergence of the optical beam106after deflection by an AOD108. For example, in a case where the optical beam106includes light at multiple wavelengths, different wavelengths will have different deflection angles214from the AOD108(e.g., based on Equation (1)). This may be true even if the frequency of the drive signal116for the AOD108has been adjusted as described previously herein. As a result, spectral variations of the optical beam106may result in varying beam divergence from the AOD108. As another example, it may be the case that different optical modes of the optical source104may produce an optical beam106with a different spot size, beam profile, and/or divergence due to different mode profiles in the optical source104. In this way, various aspects of the optical beam106prior to AOD108may vary.

Accordingly, the optical power of the adaptive optical element134may be adjusted (e.g., by a drive signal136provided by the controller110) to provide consistent beam properties (e.g., divergence, spot size, beam profile, or the like) despite variations of the optical beam106.

As an illustration, the optical power of the adaptive optical element134may be adjusted based on the signals from one or more detectors124to provide a collimated optical beam106despite variations of the optical beam106. As another illustration in the context of the system102illustrated inFIG.1B, the optical power of the adaptive optical element134may be adjusted based on the signals from one or more detectors124to provide a consistent focused spot size on the sample128(e.g., in conjunction with additional components such as the focusing optics130or the additional optics).

It is contemplated herein that the controller110may utilize any type of detector124for modifying the drive signal136to the adaptive optical element134. In some embodiments, the controller110utilizes a multi-pixel sensor array (e.g., a line sensor, an array sensor, or the like) to take advantage of the additional information provided by such a sensor. For instance, it may be desirable to adjust the optical power of the adaptive optical element134based on a spectral width of the sampled beam120, which may impact the overall divergence of the optical beam106from the AOD108along a scan direction. Accordingly, the increased spectral resolution provided by a multi-pixel sensor array may facilitate a more sensitive measurement of the spectral width than a position-sensitive detector. However, it is to be understood that this is simply an illustration and should not be interpreted as limiting. In some cases, the controller110may utilize signals from a position-sensitive detector to adjust the drive signal136to the adaptive optical element134.

Referring now again generally toFIGS.1A and1B, various additional aspects of the optical scanner100are described in greater detail, in accordance with one or more embodiments of the present disclosure.

In some embodiments, the optical scanner100includes one or more components suitable for monitoring the performance of the AOD108. For example, thermal drifts in the AOD108may impact the refractive index of the host material204and/or the modulation depth of the diffraction grating206(e.g., a magnitude of a refractive index variation Δn forming the diffraction grating206). Thermal drifts in the AOD108may thus impact the diffraction efficiency of the diffraction grating206and the power of the optical beam106deflected by the AOD108.

FIG.5is a simplified schematic of a portion of the optical scanner100including an additional detector502for monitoring the performance of the AOD108, in accordance with one or more embodiments of the present disclosure. In particular,FIG.5is a variation ofFIG.2such that the descriptions associated withFIG.2may be extended toFIG.5.

In some embodiments, the optical scanner100includes at least one additional detector502to monitor a power of at least one diffraction order of the optical beam106generated by the AOD108. For example, although the diffraction efficiency of the first-order diffraction210by the AOD108is typically high (particularly when operating in the Bragg condition), at least some power is typically provided in additional non-zero diffraction orders. For example, at least a few percent of the power of the optical beam106may be provided as second-order diffraction212and/or an additional first-order diffraction beam504having an opposite sign as the first-order diffraction210associated with the primary deflection of the optical beam106. For example, operation in the Bragg condition may provide a substantial portion of the power of the optical beam106as first-order diffraction210as described with respect toFIG.2, where the first-order diffraction210may be +1 order diffraction or −1 order diffraction based on a selected sign convention. However, it may be the case that at least some smaller portion of the power of the optical beam106may be in the additional first-order diffraction beam504of the opposite sign.

It is contemplated herein that the additional non-zero diffraction orders may advantageously be physically separated from the main scan range (e.g., the main working window) to provide easy access and does not detract from the power output of the AOD108. In contrast, some alternative techniques for monitoring thermal drift of an AOD may require injecting an additional weak drive signal to the AOD to generate weak diffraction at a different angle and tracking the stability of this weak diffraction. In some embodiments, such an additional drive signal may obviate the need for a separate dispersive element122, particularly if this additional drive signal has a higher frequency than the drive signal136. In this configuration, the detector124may be placed to capture dispersed light associated with diffraction from a grating generated by this additional drive signal (e.g., by periodic acoustic waves generated by this additional drive signal).

The controller110may then be coupled to the additional detector502to monitor the power in the associated non-zero diffraction order. For example, increased power in such a non-zero diffraction order may be indicative of thermal drift of the AOD108.

In cases where the optical beam106exhibits spectral variations, such spectral variations may further impact the power in one or more additional non-zero diffraction orders. In these cases, the controller110may isolate the relative impact of thermal drift of the AOD108from the spectral variations based on the signals from the one or more detectors124. For example, spectral variations of the optical beam106may typically occur on a shorter timescale than thermal drifts in the AOD108. Accordingly, power variations of the additional non-zero diffraction orders as measured by the additional first-order diffraction beam504that correspond to observable spectral variations may be removed or ignored by the controller110such that thermal drifts in the AOD108on relatively longer timescales may be monitored.

In some embodiments, the controller110is further configured to adjust an amplitude of the drive signal116to the AOD108based on signals from any of the one more detectors124. As described previously herein with respect toFIG.2, the amplitude of the drive signal116may control a modulation depth of the induced diffraction grating206and may thus control a diffraction efficiency of the optical beam106. In this way, the controller110may adjust the intensity or power of the optical beam106deflected by the AOD108.

In some embodiments, the controller110adjusts the amplitude of the drive signal116to provide an optical beam106with a constant power. It is contemplated herein that the power of the optical beam106may fluctuate for various reasons. In any case, the controller110may adjust the amplitude of the drive signal116to provide an optical beam106with a constant power over time.

For example, the power of the optical beam106from the optical source104may fluctuate. Such power fluctuations may be detected and provided to the controller110using any suitable technique. For instance, power fluctuations of the sampled beam120, which may include a fixed percentage of the power of the optical beam106may be monitored using any of the one or more detectors124.

As another example, the power of the optical beam106deflected by the AOD108may vary based on thermal drifts of the AOD108, which may be detected using an additional first-order diffraction beam504as described with respect toFIG.5.

As another example, the power of the optical beam106propagating through a wavelength-sensitive polarizing element (e.g., a polarization rotator, a polarizer, a polarizing beamsplitter, or the like) in response to spectral variations of the optical beam106. Such power fluctuations may be monitored by an additional detector (not shown) and/or may be predicted based on a known wavelength response of the element and the spectral variations of the optical beam106as measured by the one or more detectors124.

Referring again toFIGS.1A-1B, it is contemplated herein that the controller110may generate any of the adjustments described herein (e.g., the frequency and/or amplitude of the drive signal116for the AOD108, the drive signal136for the adaptive optical element134, or the like) using any technique known in the art.

In some embodiments, the controller110generates an adjustment using a model and/or a lookup table based on a model. As a non-limiting example in the context of generating a frequency adjustment (Δf) of the drive signal116in response to spectral variations of the sampled beam120, the relationship between the COM of the spectrally-dispersed sampled beam120in a plane of a detector124and the associated spectral variation may be determined based on the dispersion of the dispersive element122as well as the separation between the dispersive element122and the detector124. Accordingly, the controller110may directly calculate a required frequency adjustment (Δf) based on signals from the detector124or may use a look-up table including previously-calculated values.

In some embodiments, the controller110generates an adjustment using a control loop (e.g., a PID control loop, or the like) or a machine-learning based technique.

In this configuration, the optical scanner100(and/or the system102) may include one or more detectors (not explicitly shown) to monitor a particular property of the optical beam106as feedback. Further, an exact relationship between a parameter to be adjusted and the feedback is not required. Rather, the feedback is used to actively control and/or predict a required adjustment. As a non-limiting example in the context of generating a frequency adjustment (Δf) of the drive signal116, feedback from a detector monitoring a position of the optical beam106after deflection by the AOD108may provide feedback suitable for controlling the value of the frequency adjustment (Δf). As another non-limiting example in the context of adjusting a power of the optical beam106, feedback from a detector monitoring a power of the optical beam106at a desired position may provide feedback suitable for controlling the amplitude of the drive signal116. As another non-limiting example in the context of adjusting a spot size of the optical beam106(e.g., on a sample128as depicted inFIG.1B), a detector monitoring the spot size may provide feedback suitable for adjusting the drive signal136to the adaptive optical element134.

Referring now toFIG.6,FIG.6is a flow diagram illustrating steps performed in a method600for dynamic control of an optical scanner, in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and enabling technologies described previously herein in the context of the optical scanner100should be interpreted to extend to method600. It is further noted, however, that the method600is not limited to the architecture of the optical scanner100.

In some embodiments, the method600includes a step602of generating a sampled beam120from a received optical beam106, wherein the sampled beam120includes a portion of the optical beam106. For example, the step602may be implemented with a sampler118such as, but not limited to, an optical wedge or a beamsplitter.

In some embodiments, the method600includes a step604of spectrally dispersing the sampled beam120along a dispersion direction302. For example, the step604may be implemented with a dispersive element122such as, but not limited to, a prism or a diffraction grating.

In some embodiments, the method600includes a step606of detecting, with one or more detectors124, at least a portion of the sampled beam120dispersed along the dispersion direction302.

In some embodiments, the method600includes a step608of determining a center of mass of the sampled beam120dispersed along the dispersion direction302based on signals from at least one of the one or more detectors124.

In some embodiments, the method600includes a step610of generating a drive signal116for an AOD108to deflect the optical beam106along a selected deflection angle214based on the center of mass. Further, in the case of multiple AODs108(e.g., providing different scan directions), drive signals116may be generated for each of the AODs108. The drive signals116of these AODs108may be the same if they operate at the same frequency or may be different if they operate at different frequencies. For instance, operation at different frequencies may be suitable for addressing certain parts of a total 2D field of view.

In some embodiments, the method600includes a step612of deflecting the optical beam106with the AOD108driven by the drive signal116.