Acousto-optic system with phase-shifted reflector

Abstract

The present invention relates to a beam positioner generally characterized as comprising a first acousto-optic (AO) deflector (AOD) operable to diffract an incident beam of linearly polarized laser light, wherein the first AOD has a first diffraction axis and wherein the first AOD is oriented such that the first diffraction axis has a predetermined spatial relationship with a plane of polarization of the linearly polarized laser light. The beam positioner can comprise at least one phase-shifting reflector disposed in a beam path along which light can propagate from the first AOD. The at least one phase-shifting reflector can be configured and oriented to rotate a plane of polarization of light diffracted by the first AOD.

Description

[0001] Cross-reference of related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 562,047, filed September 22, 2017, which is incorporated herein by reference in its entirety. Background Technology

[0003] Acousto-optic (AO) devices, sometimes called Bragg units, use radio-frequency sound waves to diffract and shift light. These devices are commonly used in Q-switching, signal modulation in telecommunications systems, laser scanning and beam intensity control in microscopy systems, frequency shifting, and wavelength filtering in spectral systems. Many other applications are well-suited to acousto-optic devices. For example, AO deflectors (AODs) can be used in laser-based material handling systems.

[0004] In a typical AO (Analog-Operating) device, a transducer is attached to an AO medium (also called an "AO unit"), typically a crystal or glass, which is appropriately transparent to the wavelength of the light to be diffracted. An RF signal (also called a "drive signal") is applied to the transducer (e.g., from an RF driver), thereby driving the transducer to vibrate at a specific frequency to generate acoustic waves propagating in the AO medium. These waves manifest as periodic regions of amplification and compression within the AO medium, resulting in a periodically changing refractive index within the AO medium. This periodically changing refractive index functions similarly to a grating that diffracts a laser beam propagating through the AO medium.

[0005] refer to Figure 1 The AOD 100 generally includes an AO medium 102, a converter 104 attached to the AO medium 102 (i.e., at the converter end of the AO medium 102), and may also include an acoustic absorber 106 attached to the AO medium 102 (i.e., at the absorber end of the AO medium 102 opposite to the converter end). An RF driver 108 is typically electrically coupled to the input of the converter 104 to drive the AOD 100. The material used to form the AO medium 102 is selected based on the wavelength of the light in the laser beam to be deflected. The converter 104 is generally a piezoelectric converter and is operable to vibrate in response to an input RF signal (i.e., a drive signal) output by the RF driver 108. The RF driver 108 is operable to generate the final drive signal input to the converter 104.

[0006] Generally, the transducer 104 is attached to the AO medium 102 such that vibrations generated by the transducer 104 can form corresponding sound waves (e.g., as indicated by line 112) that propagate within the AO medium 102 along the diffraction axis 110 of the AOD 100 from the transducer end toward the absorber 106. Figure 1 As illustrated herein, when a driving signal (e.g., characterized by frequency, amplitude, phase, etc.) is applied to the converter 104, the converter 104 vibrates to generate an acoustic wave propagating within the AO medium 102, thereby generating a periodically changing refractive index within the AO medium 102. As known in the art, the periodically changing refractive index is used to cause a laser beam (e.g., propagating along beam path 114) to be incident on the first surface 102a of the AO medium 102 at a Bragg angle θ relative to the acoustic wave. B It propagates via AO medium 102.

[0007] The incident laser beam is diffracted to form a diffraction pattern, which typically includes zero-order and first-order diffraction peaks, and may also include higher-order diffraction peaks (e.g., second-order, third-order, etc.). As known in the art, the portion of the diffracted laser beam in the zero-order diffraction peak is called the "zero-order" beam, the portion of the diffracted laser beam in the first-order diffraction peak is called the "first-order" beam, and so on. Generally, the zero-order beam and other diffraction-order beams (e.g., the first-order beam, etc.) propagate along different beam paths after exiting the AO medium 102 (e.g., via the second surface 102b of the AO medium 102 opposite to the first surface 102a). For example, the zero-order beam propagates along the zero-order beam path, the first-order beam propagates along the first-order beam path, and so on. The angle between the zero-order and other diffraction-order beam paths (e.g., the angle θ between the zero-order and first-order beam paths) is... D This corresponds to the frequency (or multiple frequencies) in the drive signal applied to diffract the laser beam incident on the AO medium 102.

[0008] The amplitude of the applied driving signal can have a nonlinear effect on the proportion of the incident laser beam diffracted into various diffraction orders, and AOD can be driven to diffract most of the incident laser beam into a first-order beam, thereby retaining a relatively small portion of the incident laser beam in other diffraction orders (e.g., a zero-order beam). Furthermore, the frequency of the applied driving signal can be rapidly changed to scan the first-order beam (e.g., to facilitate processing different areas of the workpiece). Therefore, AOD is advantageously incorporated into laser processing systems for use in laser-based material handling to variably deflect the first-order beam onto the workpiece during processing (e.g., melting, vaporization, ablation, marking, cracking, etc.).

[0009] Laser processing systems typically include one or more beam catchers to prevent laser light propagating along the zero-order beam path (and any higher-order beam paths) from reaching the workpiece. Therefore, in a laser processing system, the first-order beam path exiting the AOD 100 can typically be considered as having been rotated or deflected (e.g., by an angle of 0°) within the AOD 100. DThe beam path 114 (also referred to herein as the "first-stage deflection angle") is orthogonal to the diffraction axis of AOD 100 and the axis along which the incident laser beam propagates within AOD 100 when AOD 100 is driven to diffract the incident laser beam (also referred to herein as the "optical axis"). Therefore, AOD 100 deflects the incident beam path 114 within a plane (also referred to herein as the "deflection plane") containing (or otherwise substantially parallel to) the diffraction axis of AOD 100 and the optical axis within AOD 100. The spatial range across which AOD 100 deflects the beam path 114 within the deflection plane is referred to herein as the "scan field" of AOD 100.

[0010] The laser processing system can incorporate multiple AODs configured in series to deflect the beam path 114 along two axes. For example, and referring to... Figure 2 The first AOD 200 and the second AOD 202 can be oriented such that their respective diffraction axes (i.e., the first diffraction axis 200a and the second diffraction axis 202a, respectively) are oriented perpendicular to each other. In this example, the first AOD 200 is operable to rotate the beam path 114 about a first rotation axis 200b (e.g., which is orthogonal to the first diffraction axis 200a), thereby deflecting the incident beam path 114 in a first deflection plane (i.e., a plane containing or otherwise substantially parallel to the first diffraction axis 200a and the optical axis within the first AOD 200), wherein the first deflection plane is orthogonal to the first rotation axis 200b. Similarly, the second AOD 202 is operable to rotate the beam path 114 about the second rotation axis 202b (e.g., which is orthogonal to the second diffraction axis 202a), thereby deflecting the incident beam path 114 in a second deflection plane (i.e., a plane containing or otherwise substantially parallel to the second diffraction axis 202a and the optical axis within the second AOD 202), wherein the second deflection plane is orthogonal to the second rotation axis 202b. In view of the above, the first AOD 200 and the second AOD 202 can be jointly characterized as multi-axis "beam positioners," and each can be selectively operated to deflect the beam path 114 within the two-dimensional scan field 204. As will be understood, the two-dimensional scan field 204 can be considered as an overlap of two one-dimensional scan fields: a first one-dimensional scan field associated with the first AOD 200 and a second one-dimensional scan field associated with the second AOD 202.

[0011] Depending on the type of AOD included in the multi-axis beam positioner, it may be necessary to rotate the polarization plane of the light (i.e., the plane of electric field oscillation) within the first-order beam path transmitted by the first AOD 200. Rotating the polarization plane would be desirable if the amount of RF drive power required to diffract most of the incident laser beam into a first-order beam is highly dependent on the polarization state of the deflected laser beam. Furthermore, if each AOD in the multi-axis beam positioner includes an AO medium 102 formed of the same material, and if each AOD uses the same type of acoustic wave to deflect the incident laser beam, and if it is necessary for the polarization state of the light in the first-order beam transmitted by the first AOD 200 to be linear and oriented in a specific direction relative to the second diffraction axis 202a, then similarly, it would be necessary to rotate the polarization state of the first-order beam transmitted by the second AOD 202 relative to the polarization state of the light in the first-order beam transmitted by the first AOD 200, simply because the orientation of the second AOD 202 is rotated relative to the orientation of the first AOD 200.

[0012] Conventionally, polarization rotation is provided by a half-wave plate, and the polarization orientation of the incident beam of laser light after the half-wave plate is a function of the polarization orientation of the half-wave plate relative to the incident beam of laser light. Half-wave plates are typically made of a material with a sufficient birefringence that exhibits moderate transparency for the specific wavelength (or wavelength range) of light to be phase-shifted. Conventional half-wave plates designed to phase-shift light at wavelengths (e.g., 9.2 μm, 9.5 μm, 10.6 μm, etc.) in the range of 9 μm (or above) to 11 μm (or above) are undesirably expensive and typically unsuitable for high-power laser applications, such as laser-based material processing utilizing CO2 lasers. Summary of the Invention

[0013] A specific example can be generally characterized as including a beam positioner comprising a first acousto-optic (AO) deflector (AOD) operable to diffract an incident beam of linearly polarized laser light, wherein the first AOD has a first diffraction axis and wherein the first AOD is oriented such that the first diffraction axis has a predetermined spatial relationship with the polarization plane of the linearly polarized laser light. The beam positioner may include at least one phase-shifting reflector disposed within a beam path along which light can propagate from the first AOD. The at least one phase-shifting reflector may be configured and oriented to rotate the polarization plane of the light diffracted by the first AOD.

[0014] Another specific example can be generally characterized as a beam positioner, which includes a first acousto-optic (AO) deflector (AOD), a second AOD, and a phase delayer inserted between the first AOD and the second AOD. At least one AOD selected from the group consisting of the first AOD and the second AOD may include an AO unit formed of a material including germanium.

[0015] Another specific example can be broadly characterized as a beam positioner, comprising a first acousto-optic (AO) deflector (AOD), a second AOD disposed within a beam path along which the laser beam can propagate from the first AOD, a phase retarder disposed within a beam path between the first and second AODs, and a reflector disposed within a beam path between the first and second AODs. The first AOD, second AOD, phase retarder, and reflector are configured such that the laser beam can propagate from the second AOD in a direction at least substantially opposite to the direction in which the laser beam is incident on the first AOD. Attached Figure Description

[0016] Figure 1 An acousto-optic deflector (AOD) is schematically shown.

[0017] Figure 2 The configuration of AOD in a multi-axis beam positioner is illustrated schematically.

[0018] Figure 3 , Figure 4 , Figure 5 and Figure 7 A perspective view of a multi-axis beam locator based on various specific examples is shown schematically.

[0019] Figure 6 and Figure 8 A graph illustrating the illustrative relationship between phase shift and incident angle for a quarter-wavelength phase-shift reflector in a multi-axis beam positioner according to various specific examples. Detailed Implementation

[0020] Specific examples are described herein with reference to the accompanying drawings. Unless otherwise explicitly stated, the size, position, and any distances between components, features, and parts are not necessarily scaled, but rather enlarged for clarity. In the drawings, the same numbers refer to the same components throughout. Therefore, the same or similar numbers may be described with reference to other drawings, even if such numbers are not mentioned or described in the corresponding drawings. Furthermore, components not indicated by reference numbers may be described with reference to other drawings.

[0021] The terminology used herein is for the purpose of describing specific instances only and is not intended to be restrictive. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one skilled in the art. As used herein, unless the context clearly indicates otherwise, the singular forms "a" and "the" are intended to include the plural forms as well. It should be understood that the term "comprise / comprising," when used in this specification, designates the presence of the stated features, integrals, steps, operations, components, and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, components, components, and / or groups thereof. Unless otherwise specified, when describing a range of values, the range includes both the upper and lower limits of the range and any subranges therein. Unless otherwise indicated, terms such as "first," "second," etc., are used only to distinguish one component from another. For example, a node may be called a "first node," and similarly, another node may be called a "second node," or vice versa.

[0022] Unless otherwise indicated, the terms “approximately,” “above,” “roughly,” etc., mean quantities, sizes, proportions, parameters, and other quantities and characteristics that are not and need not be precise, but may be approximate and / or larger or smaller as needed, reflecting tolerances, conversion factors, rounding, measurement errors, and the like, as well as other factors known to those skilled in the art. Spatial relative terms, such as “below,” “under,” “down,” “above,” and “above,” and the like, may be used herein for ease of description to describe the relationship of one component or feature to another, as illustrated in the diagrams. It should be understood that such spatial relative terms are intended to cover different orientations other than those depicted in the diagrams. For example, if the objects in the diagrams are flipped, a component described as “below” or “under” other components or features will be oriented “above” other components or features. Therefore, the illustrative term “below” may cover both above and below orientations. Objects may be oriented in other ways (e.g., rotated 90 degrees or in other orientations), and the spatial relative descriptors used in this document may be interpreted accordingly.

[0023] Specific examples of the present invention can be generally characterized as providing a multi-axis beam positioner comprising at least one phase-shifting reflector (also referred to in this art as a "phase-shifting mirror," "phase-delay mirror," "reflective phase delayer," etc.) disposed in the path of a laser beam transmitted by an AOD. The laser beam transmitted by the AOD can be generally characterized as linearly polarized, and at least one phase-shifting reflector is configured and oriented to rotate the polarization plane of the laser beam transmitted by the AOD.

[0024] exist Figure 3In one specific example shown, the multi-axis beam locator 300 may include a first AOD 302 (e.g., characterized by a first diffraction axis 302a and a first rotation axis 302b), a second AOD 304 (e.g., characterized by a second diffraction axis 304a and a second rotation axis 304b), a phase-shifting reflector 306, and an optical relay system 308 (e.g., including a pair of relay lenses 310 and 312). Generally, each of the first AOD 302 and the second AOD 304 may be provided, as discussed above with respect to AOD 100. For example, each of the first AOD 302 and the second AOD 304 may include an AO medium (such as AO medium 102), a converter (such as converter 104) attached to a converter end of the AO medium, and an absorber (such as absorber 106) of choice attached to the AO medium at an absorber end opposite to the converter end.

[0025] Although not shown, the multi-axis beam positioner 300 may include one or more RF drivers (e.g., RF driver 108) electrically coupled to the inputs of a converter (also not shown) for each of the first AOD 302 and the second AOD 304. Thus, one or more drive signals may be applied to each of the first AOD 302 and the second AOD 304 by means of the RF drivers. In response to the applied drive signal, the first AOD 302 may be operable to deflect the incident laser beam within a first deflection plane (i.e., a plane orthogonal to the first rotation axis 302b and containing or additionally parallel to the first diffraction axis 302a and the optical axis within the first AOD 302). Similarly, in response to the applied drive signal, the second AOD 304 is operable to deflect the incident laser beam in the second deflection plane (i.e., a plane orthogonal to the second rotation axis 304b and containing or additionally parallel to the second diffraction axis 304a and the optical axis within the second AOD 304).

[0026] A half-wave phase-shifting reflector 306 is provided as a half-wave phase-shifting reflector, which is configured to perform a 180-degree phase shift between the S-polarization component and the P-polarization component of the incident laser beam (e.g., a reflector surface 306a having a substantially planar shape). An optical relay system 308 is set and configured to transfer the image of the first AOD 302 to the second AOD 304. As shown herein, the beam path 114 is graphically displayed as a dotted dashed line, and the aforementioned components of the multi-axis beam locator 300 are configured to propagate laser light diffraction (e.g., with respect to the first AOD 302 and the second AOD 304), refraction (e.g., with respect to the optical relay system 308), or reflection (e.g., with respect to the half-wave phase-shifting reflector 306) along the beam path 114.

[0027] First AOD 302 and second AOD 304 each provide as longitudinal mode AODs. Therefore, the polarization plane of the laser light incident on any particular AOD is parallel to (or at least substantially parallel to) the polarization plane of the laser light exiting that AOD. Multi-axis beam positioner 300 is configured to operate on linearly polarized laser light, and thus provides laser light propagating along beam path 114 and incident on the first AOD 302 to be linearly polarized (or at least substantially linearly polarized) by any means known in the art, and the first AOD 302 is oriented such that the first diffraction axis 302a is parallel to (or at least substantially parallel to) the polarization plane of the laser beam incident on the first AOD 302. Similarly, the laser light propagating along beam path 114 and incident on the second AOD 304 is linearly polarized (or at least substantially linearly polarized), and the second AOD 304 is oriented such that the second diffraction axis 304a is parallel (or at least substantially parallel) to the polarization plane of the laser light beam incident on the second AOD 304.

[0028] A half-wave phase-shifting reflector 306 is configured such that the polarization plane of the laser light incident on the reflector surface 306a (i.e., after the first AOD 302 is emitted) is rotated by 90 degrees (i.e., relative to the first deflection plane of the first AOD 302). To achieve this, and as will be discussed in more detail below, the half-wave phase-shifting reflector 306 is oriented such that the laser beam is incident on the reflector surface 306a at an incident angle of 45 degrees (or approximately). Furthermore, the half-wave phase-shifting reflector 306 is oriented such that the polarization plane of the incident laser beam is at an angle of 45 degrees (or at least substantially 45 degrees) relative to the incident / reflection plane at the reflector surface 306a.

[0029] During operation, the frequencies contained in any drive signal to be applied to the first AOD 302 can generate a range of frequencies of a first-order diffracted beam propagating from the first AOD 302 at a first-order deflection angle 0D when applied to the first AOD 302, which is within the range of a first-order deflection angle (also referred to herein as the "first-order deflection angle range"). The expected frequency range can be conceptually considered as a frequency band spanning a frequency range demarcated by low and high frequencies.

[0030] In one specific example, the orientation of the half-wave phase-shift reflector 306 relative to the first AOD 302 is fixed. Therefore, during operation of the first AOD 302, the first-order beam path 114 emanating from the first AOD 302 can be incident on the reflector surface 306a at one of many possible angles of incidence (i.e., depending on the frequency contained in the drive signal applied to the first AOD 302 during operation). In one specific example, the half-wave phase-shift reflector 306 is oriented such that when the frequency of the drive signal applied to the first AOD 302 is equal to a reference frequency within a frequency band of the intended frequency range, the first-order beam path 114 emanating from the first AOD 302 is incident on the reflector surface 306a at an angle of incidence of 45 degrees (or vertically or additionally at an angle of incidence of at least substantially 45 degrees). The frequency band can be equal to 2MHz, 5MHz, 10MHz, 15MHz, 20MHz, 25MHz, 30MHz, etc., or any of these values, and the lower frequency of the band can be equal to 25MHz, 30MHz, 35MHz, 40MHz, 45MHz, 50MHz, 55MHz, 60MHz, etc., or any of these values. Therefore, the reference frequency can be any frequency in the range of 26kHz (or around 26kHz) to 89MHz (or around 89MHz). In a specific instance, the reference frequency can be 30MHz, 40MHz, 50MHz, 60MHz, 70MHz, 80MHz, etc., or any of these values. Generally speaking, the reference frequency is located in or near the middle of the expected frequency range. In a specific instance, when the reference frequency is within 15%, 10%, 5%, 2%, 1%, 0.5%, 0.25%, 0.1%, etc., of the middle frequency of the band, or any of these values, the reference frequency is near the middle of the expected frequency range.

[0031] In another specific example, the orientation of the half-wave phase-shift reflector 306 relative to the first AOD 302 can be variable. For instance, the half-wave phase-shift reflector 306 can be rotated to ensure that, when the frequency of the drive signal applied to the first AOD 302 is within a sub-range of the desired frequency, the first-order beam path 114 exiting the first AOD 302 is incident on the reflector surface 306a at an angle of incidence of 45 degrees (or above, below, or otherwise at an angle of incidence of at least substantially 45 degrees). The desired frequency sub-range can be considered as a frequency band spanning a frequency sub-range demarcated by low and high frequencies (which may be equal to or lower than the desired frequency range). To facilitate rapid adjustment of the orientation of the half-wave phase shift reflector 306 relative to the first 302, the half-wave phase shift reflector 306 may be mounted to a platform actuated by a voice coil actuator, a piezoelectric positioner, a micro-electro-mechanical system (MEMS) positioner or the like or any combination thereof, or the half-wave phase shift reflector 306 may be provided as a deformable mirror or the like or any combination thereof.

[0032] As shown, the phase-shifting reflector 306 is positioned in the beam path 114 between the first AOD 302 and the optical relay system 308. However, in another specific embodiment, the phase-shifting reflector 306 may be positioned in the beam path 114 between a pair of relay lenses 310 and 312 of the optical relay system 308. In yet another specific embodiment, the phase-shifting reflector 306 may be positioned in the beam path 114 between the optical relay system 308 and the second AOD 304.

[0033] When oriented and configured as described above, the half-wave phase-shift reflector 306 rotates the polarization plane of the incident laser beam by 90 degrees relative to the first polarization plane of the first AOD 302 (i.e., around the optical axis of the laser beam's propagation). Furthermore, as... Figure 3 As illustrated, the half-wave phase-shifting reflector 306 skews the orientation of the beam path 114, which may make it difficult to assemble the components of the multi-axis beam positioner 300 into a relatively compact package. To facilitate a more compact assembly of the multi-axis beam positioner 300, a mirror configured to impart zero (or at least substantially zero) phase shift (also referred to herein as a "zero-phase-shift reflector") can be provided to fold the beam path 114 in any suitable or desired manner, thereby providing a more compact multi-axis beam positioner.

[0034] For example and reference Figure 4 A zero-phase-shift reflector 402 (e.g., having a substantially planar reflector surface 402a) can be inserted into the beam path 114 between the half-wave phase-shift reflector 306 and the lens 310 of the multi-axis beam positioner 300 (thus creating the multi-axis beam positioner 400). Figure 4As illustrated, the zero-phase-shift reflector 402 can be oriented such that the laser beam reflected by the zero-phase-shift reflector 402 propagates in a direction substantially opposite to the direction in which the laser beam propagates to the half-wave phase-shift reflector 306 upon incident, and such that the first polarization plane of the first AOD 302 upon reflection from the zero-phase-shift reflector 402 is rotated by 90 degrees relative to the orientation of the first deflection plane upon incident on the reflector surface 306a. Because the zero-phase-shift reflector 402 does not impart any (or any substantial) phase shift, the polarization plane of the laser beam reflected at the reflector surface 402a does not change (or changes by a negligible amount) relative to the first polarization plane of the first AOD 302. As a result, the polarization direction of the linearly polarized laser light finally delivered to the second AOD 304 will be parallel to (or at least substantially parallel to) the polarization direction of the linearly polarized laser light output from the first AOD 302. Therefore, as Figure 4 As shown, the second diffraction axis 304a of the second AOD 304 may be parallel to (or at least substantially parallel to) the first diffraction axis 302a of the first AOD 302. Furthermore, when projected onto the second AOD 304 (e.g., from the zero-phase-shift reflector 402 via the optical relay system 308), the first polarization plane of the first AOD 302 will be perpendicular to (or at least substantially perpendicular to) the second polarization plane of the second AOD 304. Therefore, when projected onto the second AOD 304, the scan field (one-dimensional scan field) associated with the first AOD 302 will be perpendicular to (or at least substantially perpendicular to) the scan field (also a one-dimensional scan field) associated with the second AOD 304, and the multi-axis beam positioner 400 can be considered as having a two-dimensional scan field characterized by the overlap of the two one-dimensional scan fields associated with the first AOD 302 and the second AOD 304.

[0035] Typically, the amount of phase shift (also referred to as "phase delay") imparted by the half-wave phase-shift reflector 306 to the incident laser beam propagating along beam path 114 varies with the angle of incidence of beam path 114 at reflector surface 306a (e.g., as a result of changing the driving frequency of the first AOD 302). This phase shift will cause a deviation in the polarization state of the beam incident on the second AOD 304, so that it is no longer linearly polarized in the desired axis, but elliptically polarized. To eliminate or further reduce the effect of the variable angle of incidence of beam path 114 at reflector surface 306a, the half-wave phase-shift reflector 306 can be replaced by a pair of quarter-wave phase-shift reflectors. For example, and as Figure 5 As shown in the figure, it can provide something similar to that of other languages. Figure 3The multi-axis beam positioner 300 shown in the figure describes the multi-axis beam positioner 500, but the half-wave phase-shifting reflector 306 is replaced by a pair of quarter-wave phase-shifting reflectors (i.e., a first phase-shifting reflector 502 having a substantially planar reflector surface 502a and a second phase-shifting reflector 504 having a substantially planar reflector surface 504a) disposed within the beam path 114.

[0036] like Figure 5 As illustrated, the first quarter-wavelength phase-shifting reflector 502 is oriented such that when the frequency of the drive signal applied to the first AOD 302 is equal to the aforementioned reference frequency within the expected frequency range, the laser beam propagating along the beam path 114 will be incident on the reflector surface 502a at an angle of incidence of 45 degrees (also referred to as the "first angle of incidence") (or around 45 degrees, or otherwise at at least substantially 45 degrees). The first quarter-wavelength phase-shifting reflector 502 is further oriented to ensure that when the frequency of the drive signal applied to the first AOD 302 is equal to the aforementioned reference frequency within the expected frequency range, the light reflected from the reflector surface 502a contains equal (or at least substantially equal) amounts of S and P polarization components (i.e., so that the light reflected from the reflector surface 502a is circularly polarized or at least substantially circularly polarized). When oriented as described above, the first quarter-wavelength phase-shifting reflector 502 is thus configured to perform a 90-degree (or approximately 90-degree) phase shift between the S-polarization component and the P-polarization component of the incident laser beam.

[0037] The second quarter-wavelength phase-shifting reflector 504 is oriented such that its reflector surface 504a is perpendicular (or at least substantially perpendicular) to the reflector surface 502a of the first quarter-wavelength phase-shifting reflector 502. Therefore, the surface normal of the reflector surface 504a of the second quarter-wavelength phase-shifting reflector 504 is perpendicular (or at least substantially perpendicular) to the surface normal of the reflector surface 502a of the first quarter-wavelength phase-shifting reflector 502. When oriented as described above, the second quarter-wavelength phase-shifting reflector 504 is configured to perform a 90-degree (or approximately 90-degree) phase shift between the S-polarization and P-polarization components of the incident laser beam. Therefore, circularly polarized (or at least substantially circularly polarized) light incident on the reflector surface 504a will be reflected as linearly polarized (or at least substantially linearly polarized) light.

[0038] To facilitate a combined phase shift of 180 degrees (or around 180 degrees) from a pair of quarter-wavelength phase-shifting reflectors 502 and 504 in the multi-axis beam positioner 500, the first quarter-wavelength phase-shifting reflector 502 is configured to have the same (or substantially the same) phase shift characteristics (which may be at least substantially linear) as the second quarter-wavelength phase-shifting reflector 504 within the same incident angle range. Figure 6 A graph illustrating the exemplary phase shift characteristics of each of the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 within the same incident angle range. The amount of phase shift imparted by the first quarter-wavelength phase-shifting reflector 502 or the second quarter-wavelength phase-shifting reflector 504 at any particular incident angle may vary depending on one or more factors (e.g., as indicated by the error bar), such factors as the material of the reflector surface used to make the quarter-wavelength phase-shifting reflector, the temperature of the reflector surface, the presence, amplitude, and orientation of any mechanical strain at the reflector surface, or similar factors or any combination thereof.

[0039] When the first-order beam path 114 of the first AOD 302 is incident on the reflector surface 502a at a first incident angle of 45 degrees, the first quarter-wavelength phase-shifting reflector 502 imparts a 90-degree phase shift to the linearly polarized laser light incident thereon, and reflects a beam of laser light that is at least substantially circularly polarized (e.g., having at least substantially equal S and P polarization components). However, and as Figure 6 As illustrated, when the first incident angle deviates from 45 degrees, the phase shift imparted by the first quarter-wavelength phase-shifting reflector 502 deviates by 90 degrees accordingly, thereby generating a reflected beam of laser light with increasingly elliptical polarization.

[0040] For example, when the first incident angle increases to above 45 degrees, the first quarter-wavelength phase-shifting reflector 502 will produce a phase shift greater than 90 degrees (i.e., "upward shift"). When the incident angle is smaller than 45 degrees, the first quarter-wavelength phase-shifting reflector 502 will produce a phase shift less than 90 degrees (i.e., "downward shift"). However, when the second quarter-wavelength phase-shifting reflector 504 is oriented as described above, the second incident angle (i.e., the incident angle of the laser beam incident on the reflector surface 504a) is complementary to the first incident angle. That is, the sum of the first and second incident angles is 90 degrees. Therefore, the upward shift produced by the first quarter-wavelength phase-shifting reflector 502 is compensated by an equal (or approximately or at least substantially equal) but opposite downward shift produced by the second quarter-wavelength phase-shifting reflector 504. Similarly, the downward shift produced by the first quarter-wavelength phase-shifting reflector 502 is compensated by an equal (or approximately or at least substantially equal) but opposite upward shift produced by the second quarter-wavelength phase-shifting reflector 504. The net result is that the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 can together perform a combined phase shift of 180 degrees (or approximately 180 degrees) between the S and P components of the laser beam incident on the first quarter-wavelength phase-shifting reflector 502 within the incident angle range.

[0041] When oriented and configured as described above, the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 of the multi-axis beam positioner 500 are used together to rotate the polarization plane of the laser beam output from the first AOD 302 relative to the first deflection plane of the first AOD 302 (e.g., rotate by 90 degrees or more), and also to rotate the orientation of the first deflection plane of the first AOD 302 relative to the first deflection plane incident on the reflector surface 502a (e.g., rotate by 90 degrees or more). The multi-axis beam positioner 500 can be regarded as having a two-dimensional scanning field characterized by the overlap of two one-dimensional scanning fields associated with the first AOD 302 and the second AOD 304.

[0042] like Figure 5 As shown, the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 are positioned between the first AOD 302 and the optical relay system 308. However, in another specific embodiment, the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 may be positioned between a pair of relay lenses 310 and 312 of the optical relay system. In yet another specific embodiment, the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 may be positioned between the optical relay system 308 and the second AOD 302. In yet another specific embodiment, the first quarter-wavelength phase-shifting reflector 502 may be positioned between any pair of components in the multi-axis beam positioner 500, and the second quarter-wavelength phase-shifting reflector 504 may be optically positioned downstream of the first quarter-wavelength phase-shifting reflector 502, between another pair of components in the multi-axis beam positioner 500.

[0043] In another specific example, the multi-axis beam positioner 500 may be modified such that the reflector surface 504a of the second quarter-wavelength phase-shift reflector 504 is parallel to (or at least substantially parallel to) the reflector surface 502a of the first quarter-wavelength phase-shift reflector 502 (thereby obtaining) Figure 7 The multi-axis beam positioner 700 shown in the figure. Except that the reflector surfaces 502a and 504a are parallel (or at least substantially parallel) to each other, the reflection plane of the second quarter-wavelength phase-shifting reflector 504 is the same as (or at least substantially coplanar) with the reflection plane of the first quarter-wavelength phase-shifting reflector 502. Therefore, the surface normal of the reflector surface 504a of the second quarter-wavelength phase-shifting reflector 504 will be parallel (or at least substantially parallel) to the surface normal of the reflector surface 502a of the first quarter-wavelength phase-shifting reflector 502.

[0044] To facilitate a combined phase shift of 180 degrees (or approximately 180 degrees) from a pair of quarter-wavelength phase-shifting reflectors 502 and 504 in the multi-axis beam positioner 700, the first quarter-wavelength phase-shifting reflector 502 is configured to have a different phase-shifting characteristic (which may be at least substantially linear) from that of the second quarter-wavelength phase-shifting reflector 504 within the same incident angle range. Specifically, one of the first quarter-wavelength phase-shifting reflector 502 or the second quarter-wavelength phase-shifting reflector 504 is configured to produce a phase downshift between the S-polarization and P-polarization components at a given incident angle (by any suitable or advantageous means known in this art), while the other of the first quarter-wavelength phase-shifting reflector 502 or the second quarter-wavelength phase-shifting reflector 504 is configured to produce a phase upshift between the S-polarization and P-polarization components at the same given incident angle. Figure 8 A graph illustrating the exemplary phase shift characteristics of either the first quarter-wavelength phase-shift reflector 502 or the second quarter-wavelength phase-shift reflector 504 within the same incident angle range is provided. For example, the first quarter-wavelength phase-shift reflector 502 may have… Figure 6 The phase shift characteristics shown are illustrated, and the second quarter-wavelength phase-shifting reflector 504 may have... Figure 8 The phase shift characteristics shown are, or vice versa.

[0045] like Figure 6 and Figure 8 As shown, the combined magnitude of the downward and upward shifts at the common incident angle will be 180 degrees (or approximately 180 degrees). For example, at a 45-degree incident angle, both quarter-wavelength phase-shifting reflectors produce a 90-degree phase shift. At a 43-degree incident angle, one of the quarter-wavelength phase-shifting reflectors produces an 83-degree phase shift (see [reference]). Figure 6 The other one in the quarter-wavelength phase-shift reflector produces a 97-degree phase shift (see...). Figure 8 At an incident angle of 46 degrees, one of the quarter-wavelength phase-shifting reflectors produces a 94-degree phase shift (see...). Figure 6 The other one in the quarter-wavelength phase-shift reflector produces an 86-degree phase shift (see...). Figure 8 ).

[0046] When oriented and configured as described above, the first quarter-wavelength phase-shifting reflector 502 and the second quarter-wavelength phase-shifting reflector 504 of the multi-axis beam locator 700 are used together to rotate the polarization plane of the laser beam output from the first AOD 302 relative to the first deflection plane of the first AOD 302 (e.g., rotate by 90 degrees or approximately 90 degrees). However, unlike the specific example discussed above regarding the multi-axis beam locator 500, in the multi-axis beam locator 700, the pair of quarter-wavelength phase-shifting reflectors does not rotate the first polarization plane of the first AOD 302 relative to the polarization plane of the laser beam incident on the reflector surface 502a of the first quarter-wavelength phase-shifting reflector 502. The pair of quarter-wavelength phase-shifting reflectors can also be considered as redirecting the beam path 114 so that the light reflected from the reflector surface 504a propagates in a direction substantially the same as the direction in which the laser beam is incident on the reflector surface 502a of the first quarter-wavelength phase-shifting reflector 502. As a result, the polarization direction of the linearly polarized laser light finally delivered to the second AOD304 in the multi-axis beam positioner 700 will be perpendicular (or at least substantially perpendicular) to the polarization direction of the linearly polarized laser light output from the first AOD302. Therefore, as Figure 7 As shown, the second diffraction axis 304a of the second AOD 304 may be perpendicular to (or at least substantially perpendicular to) the first diffraction axis 302a of the first AOD 302. Furthermore, when projected onto the second AOD 304 (e.g., from the second quarter-wavelength phase-shifting reflector 504 via the optical relay system 308), the first polarization plane of the first AOD 302 will be perpendicular to (or at least substantially perpendicular to) the second polarization plane of the second AOD 304. Therefore, when projected onto the second AOD 304, the scan field (one-dimensional scan field) associated with the first AOD 302 will be perpendicular to (or at least substantially perpendicular to) the scan field (also a one-dimensional scan field) associated with the second AOD 304, and the multi-axis beam positioner 700 can be considered as having a two-dimensional scan field characterized by the overlap of the two one-dimensional scan fields associated with the first AOD 302 and the second AOD 304.

[0047] Based on the above discussion, it is assumed that in the multi-axis beam locator 700, the orientation of the first quarter-wavelength phase-shifting reflector 502 relative to the first AOD 302 is fixed, and the orientation of the second quarter-wavelength phase-shifting reflector 504 relative to the first quarter-wavelength phase-shifting reflector 502 is also fixed. In this specific example, and unlike regarding... Figure 5In the specific examples discussed, if the two phase-shifting reflectors impart the same phase shift between the S-polarization component and the P-polarization component at an incident angle different from the incident angle that imparts a 90-degree phase shift between the S-polarization component and the P-polarization component, then the second quarter-wavelength phase-shifting reflector 504 will not compensate for the upward or downward shift. However, in other specific examples, the orientation of the first quarter-wavelength phase-shifting reflector 502 relative to the first AOD 302 may be variable, the orientation of the second quarter-wavelength phase-shifting reflector 504 relative to the first AOD 302 may be variable, the orientation of the first quarter-wavelength phase-shifting reflector 502 relative to the second quarter-wavelength phase-shifting reflector 504 may be variable, the orientation of the second quarter-wavelength phase-shifting reflector 504 relative to the first quarter-wavelength phase-shifting reflector 502 may be variable, or similar combinations thereof. For example, the first quarter-wavelength phase-shifting reflector 502 may (e.g., independently of or in conjunction with the second quarter-wavelength phase-shifting reflector 504) rotate to ensure that, when the frequency of the drive signal applied to the first AOD 302 is within the aforementioned expected frequency sub-range, the first-order beam path 114 exiting the first AOD 302 is incident on the reflector surface 502a at an angle of incidence of 45 degrees (or at least substantially 45 degrees). In another example, the second quarter-wavelength phase-shifting reflector 504 may rotate relative to the first quarter-wavelength phase-shifting reflector 502 to compensate for any upward or downward shifts caused by the first quarter-wavelength phase-shifting reflector 502 when the frequency of the drive signal applied to the first AOD 302 is within the aforementioned expected frequency sub-range. To facilitate rapid adjustment of the orientation of any of the half-wave phase shift reflectors, one or both of the half-wave phase shift reflectors may be mounted to a platform actuated by a voice coil actuator, piezoelectric positioner, microelectromechanical system (MEMS) positioner or the like or any combination thereof, or one or both of the half-wave phase shift reflectors may be provided as deformable mirrors or the like or any combination thereof.

[0048] In one specific example, the material of the AO medium 102 forming the first AOD 302 and the second AOD 304 is typically selected to deflect light having wavelengths in the range of 2 μm to 20 μm, such as germanium (Ge). Therefore, the laser beam propagating along the beam path 114 can have a wavelength in the range of 2 μm to 20 μm, and in one specific example, the wavelength is in the range of 9 μm to 11 μm. Exemplary wavelengths may include 9.4 μm, 9.6 μm, 10.6 μm, etc., or around or between these values. Such a laser beam can be generated by any suitable laser source (e.g., a high-power CO2 laser capable of outputting a laser beam at an average power ranging from 20 W (or around 20 W) to 20 kW (or around 20 kW), as known in the art). Materials that can form any of the aforementioned phase-shift reflectors may include materials such as silicon, copper, molybdenum, gold, or similar materials or any combination thereof, and as is known in the art, the material is typically selected depending on the wavelength of the light in the laser beam to be deflected. For example, the AO units of the first AOD 302 and the second AOD 304 may be formed of germanium (Ge), and any phase-shift reflector of any of the multi-axis beam positioners 300, 400, 500, or 700 may be formed of materials such as silicon or copper and may include a plurality of coatings, as is known in the art.

[0049] In the specific examples discussed above, multi-axis beam positioners 300, 400, 500, and 700 are provided as multi-axis beam positioners having two AODs (i.e., a first AOD 200 and a second AOD 202). In other specific examples, the beam positioner may include a single AOD or more than two AODs. In a specific example where the beam positioner includes a single AOD, the beam positioner may include at least one phase-shifting reflector (e.g., at least one half-wave phase-shifting reflector, at least one quarter-wave phase-shifting reflector, or the like or any combination thereof) disposed at the optical output of the AOD. In a specific example where the beam positioner includes more than two AODs, the beam positioner may or may not include at least one phase-shifting reflector disposed in any AOD at the optical output of the beam path from its feed to the other AOD (e.g., as described above regarding...). Figure 3 , Figure 4 , Figure 5 or Figure 7 (as described by any of them).

[0050] In the specific examples discussed above, the beam positioner is described as including one or more AODs as beam deflection devices. It should be understood that the beam positioner may additionally include one or more other beam deflection devices (e.g., configured to deflect any beam transmitted by any of the aforementioned AODs). In this case, any of such other beam deflection devices may include an electro-optic deflector (EOD), a fast-steering mirror (FSM) assembly actuated by a piezoelectric actuator, electrostrictive actuator, voice coil actuator, etc., a galvanometer-type mirror, a rotating polygonal mirror scanner, etc., or similar or any combination thereof.

[0051] The foregoing description of specific examples and embodiments of the present invention should not be construed as limiting it. Although several specific examples and embodiments have been described with reference to the drawings, it will be readily apparent to those skilled in the art that numerous modifications to the disclosed specific examples and embodiments, as well as other specific examples, are possible without significantly departing from the novel teachings and advantages of the present invention.

[0052] For example, although the specific examples presented above have illustrated the use of half-wave phase-shifting reflectors or a pair of quarter-wave phase-shifting reflectors to rotate the polarization plane of light output from the first AOD 302, it should be understood that any other type of phase-shifting reflector or combination of phase-shifting reflectors (with or without the cooperation of one or more zero-phase-shifting reflectors) may be used, provided that such reflectors are configured and oriented to impart a 180-degree (or approximately 180-degree) phase shift between the S and P components of the polarized light in the laser beam propagating along beam path 114, so as to rotate the polarization plane of light output from the first AOD 302 by 90 degrees (or approximately 90 degrees) relative to the first deflection plane of the first AOD 302.

[0053] Furthermore, although the above discussion of the materials of the AO medium 102 forming the first AOD 200 and the second AOD 202 has been limited to germanium, it should be understood that the material of the AO medium 102 for either the first AOD 200 or the second AOD 202 can be any other suitable material, such as gallium arsenide (GaAs), lumbromine (PbMoO4), tellurium dioxide (TeO2), crystalline quartz, glassy SiO2, arsenic trisulfide (As2S3), LiNbO3, or the like, and as is known in the art, it is typically selected depending on the wavelength of the light in the laser beam to be deflected. Therefore, as is known in the art, the material that can form the aforementioned phase-shift reflector will also depend on the wavelength of the light in the laser beam to be reflected. Exemplary materials that can form any phase-shift reflector may include materials such as glass, fused silica, crystalline quartz, silicon, copper, molybdenum, gold, silicon carbide, aluminum, or the like or any combination thereof.

[0054] Furthermore, although the specific examples presented above have discussed the use and configuration of AODs having diffraction axes parallel to (or at least substantially parallel to) the polarization plane of the laser beam incident on the AOD, the principles discussed herein can be applied to other specific examples involving the use of AODs having diffraction axes perpendicular to (or at least substantially perpendicular to) the polarization plane of the laser beam incident on the AOD. For example, each of the first AOD 302 and the second AOD 304 (i.e., in any of the multi-axis beam positioners 300, 400, 500, or 700) may have an AO unit formed of a material such as crystalline quartz and oriented such that, as the laser beam propagates along beam path 114, the diffraction axis of each of these AODs is perpendicular to (or at least substantially perpendicular to) the polarization plane of the laser beam incident on each AOD. In this specific example, the laser beam has a wavelength in the ultraviolet, visible, or other infrared range of the electromagnetic spectrum and is linearly polarized.

[0055] Furthermore, although the specific examples presented above have described multi-axis beam positioners 300, 400, 500, or 700 as including an optical relay system 308, it should be understood that the optical relay system 308 may be omitted.

[0056] Furthermore, although embodiments in which the phase-shifting reflector is used in various ways to impart a phase shift to the laser beam output from the first AOD 302 have been discussed above, it should be understood that one or more transmission phase-shifting plates may also be used (e.g., in addition to those discussed above). Figure 3 , Figure 4 , Figure 5 or Figure 7 (Other than or as a substitute for any of the phase-shifting reflectors discussed in any of the above). Generally, the transmission phase shifter is at least substantially transparent to the wavelength of the laser beam that will propagate along the beam path 114. For example, a transmission phase shifter (such as a structured diamond half-wave plate) may be inserted into the beam path 114 to impart a 180° phase shift to the laser beam output from the first AOD 302 when the laser beam propagating along the beam path 114 has a wavelength in the range of 9 μm to 11 μm (e.g., 9.4 μm, 9.6 μm, 10.6 μm, etc., or around or between these values).

[0057] Therefore, all these modifications are intended to be included within the scope of the invention as defined in the claims. For example, those skilled in the art will understand that the object of any sentence, paragraph, instance, or specific instance can be combined with some or all of the objects of other sentences, paragraphs, instances, or specific instances, unless such combinations are mutually exclusive. The scope of the invention should therefore be determined by the following claims, and equivalents of such technical solutions are included within the scope of the invention.

Claims

1. A multi-axis beam positioner for deflecting a beam path in a two-dimensional scanning field, wherein a beam of diffracted linearly polarized laser light propagates along the beam path, the multi-axis beam positioner comprising: A first acousto-optic deflector is used to diffract the laser light to deflect the beam path into a first one-dimensional scanning field, the first one-dimensional scanning field extending along a first axis of the two-dimensional scanning field. The second acousto-optic deflector is operationally used to diffract the laser light to deflect the beam path into a second one-dimensional scanning field, which extends along the second axis of the two-dimensional scanning field. as well as At least one reflection phase delayer is disposed between the first acousto-optic deflector and the second acousto-optic deflector. The at least one reflective phase delayer is configured and oriented to rotate the polarization plane of the laser light diffracted by the first acousto-optic deflector. Wherein, the first acousto-optic deflector, the second acousto-optic deflector, and the at least one reflective phase retarder are configured such that the first one-dimensional scan field is incident on the at least one reflective phase retarder, such that: The first one-dimensional scanning field is projected from the at least one reflective phase retarder onto the second acousto-optic deflector in such a manner that the first axis is perpendicular to the second axis; and The polarization plane of the laser light diffracted by the first acousto-optic deflector and incident on the second acousto-optic deflector is parallel to the diffraction axis of the second acousto-optic deflector.

2. The multi-axis beam locator as described in claim 1, wherein, The first acousto-optic deflector has a first diffraction axis. The second acousto-optic deflector has a second diffraction axis, and The first and second acousto-optic deflectors are configured such that the first diffraction axis is parallel to the second diffraction axis.

3. The multi-axis beam locator as described in claim 1, wherein... The first acousto-optic deflector has a first diffraction axis. The second acousto-optic deflector has a second diffraction axis, and The first and second acousto-optic deflectors are configured such that the first diffraction axis is perpendicular to the second diffraction axis.

4. The multi-axis beam locator of claim 1, wherein the at least one reflection phase delayer comprises a half-wave reflection phase delayer.

5. The multi-axis beam locator of claim 1, wherein the at least one reflective phase delayer comprises two quarter-wavelength reflective phase delayers.

6. The multi-axis beam locator of claim 5, wherein the two quarter-wavelength reflection phase delayers comprise: A first quarter-wavelength reflective phase retarder having a first reflector surface; and The second quarter-wavelength reflective phase retarder has a second reflector surface. The first quarter-wavelength reflective phase retarder and the second quarter-wavelength reflective phase retarder are oriented relative to each other such that the surface normal of the first reflector surface is perpendicular to the surface normal of the second reflector surface.

7. The multi-axis beam positioner of claim 1, wherein the first acousto-optic deflector comprises an acousto-optic unit formed of a material including germanium.

8. The multi-axis beam positioner of claim 1, wherein the first acousto-optic deflector comprises an acousto-optic unit formed of a material including quartz.

9. The multi-axis beam positioner of claim 1, wherein the first one-dimensional scanning field is projected onto the second acousto-optic deflector such that the first axis is perpendicular to the second axis.

10. The multi-axis beam positioner of claim 1 further includes an optical relay system disposed between the first acousto-optic deflector and the second acousto-optic deflector, such that the first one-dimensional scanning field is projected onto the second acousto-optic deflector through the optical relay system.

11. The multi-axis beam positioner of claim 1, further comprising an optical relay system disposed between the first acousto-optic deflector and the second acousto-optic deflector, such that the first one-dimensional scanning field is projected onto the second acousto-optic deflector through the optical relay system, wherein at least one reflection phase delayer is disposed between the first acousto-optic deflector and the optical relay system.

12. The multi-axis beam positioner of claim 1, further comprising an optical relay system disposed between the first acousto-optic deflector and the second acousto-optic deflector, such that the first one-dimensional scanning field is projected onto the second acousto-optic deflector through the optical relay system, wherein at least one reflection phase delayer is disposed between the second acousto-optic deflector and the optical relay system.

13. The multi-axis beam positioner of claim 1, further comprising an optical relay system disposed between the first acousto-optic deflector and the second acousto-optic deflector, such that the first one-dimensional scanning field is projected onto the second acousto-optic deflector through the optical relay system, wherein the optical relay system comprises a pair of lenses, and wherein at least one reflection phase delayer is disposed between the lenses of the pair of lenses.

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