Germanium AOD system with parallel and perpendicular orientation

Abstract

Numerous examples of multi-axis beam positioners are disclosed that can deflect a beam path along a laser light along multiple axes. The beam positioner includes a first AOD and a second AOD arranged in optical series with each other. The first AOD and the second AOD are arranged and configured to deflect the beam path along different axes of the multi-axis beam positioner. In one example, the AO cell of the first AOD is formed from the same material as the AO cell of the second AOD, but the first AOD is configured differently than the second AOD. In another example, the first AOD and the second AOD are longitudinal mode AODs, and there is no retarder between the first AOD and the second AOD. In another example, a heat exchanger is provided to cool the AO cell of the second AOD relative to the AO cell of the first AOD.

Description

[Technical field]

[0001] background I.Technical field SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate generally to acousto-optic deflectors, beam positioning systems incorporating same, and techniques for operating same. [Background technology]

[0002] II. Description of Related Art Acousto-optic (AO) devices, also called Bragg cells, use radio frequency sound waves to diffract and shift light. These devices are often used for Q-switching, signal modulation in communications systems, laser scanning and beam intensity control in microscopy systems, frequency shifting, and wavelength filtering in spectroscopy systems. Many other applications are also suitable for the use of acousto-optic devices. For example, AO deflectors (AODs) can be used in laser-based materials processing systems.

[0003] In a typical AO device, a transducer is attached to an AO medium (also called an "AO cell"), which is typically a crystal or glass that is suitably transparent to the wavelength of light to be diffracted. An RF signal (also known as a "drive signal") is applied to the transducer (e.g., from an RF driver), which drives the transducer to vibrate at a frequency and propagates acoustic waves into the AO medium that appear as periodic regions of expansion and contraction, thereby creating a periodically varying refractive index in the AO medium. The periodically varying refractive index acts like an optical grating that can diffract a laser light beam propagating through the AO medium.

[0004] With reference to FIG. 1, the AOD 100 generally includes an AO medium 102, a transducer 104 attached to the AO medium 102 (at a transducer end of the AO medium 102), and may further include an acoustic absorber 106 attached to the AO medium 102 (at an absorber end of the AO medium 102 opposite the transducer end). While FIG. 1 illustrates a configuration in which a single transducer 104 is attached to the AO medium 102, it will be appreciated that multiple transducers 104 (e.g., arranged in a linear array) may be attached to the AO medium 102 at its transducer end. To drive the AOD 100, an RF driver 108 is electrically connected to an input of each transducer 104. The material forming the AO medium 102 is selected according to the wavelength of light in the laser light beam to be deflected. The transducers 104 are typically formed from a piezoelectric material and are operable to vibrate in response to an input RF signal output by the RF driver 108. The RF driver 108 is operable to generate a drive signal that is ultimately input to the transducers 104.

[0005] In general, the transducer 104 is mounted on the AO medium 102 such that vibrations generated by the transducer 104 generate corresponding acoustic waves (e.g., longitudinal mode acoustic waves as indicated by lines 112) that propagate within the AO medium 102 along the diffraction axis (indicated by arrow 110) of the AOD 100 from the transducer end toward the acoustic absorber 106. As exemplarily shown in FIG. 1 , when an RF drive signal (e.g., characterized by frequency, amplitude, phase, etc.) is applied to the transducer 104, the transducer 104 vibrates to generate acoustic waves that propagate within the AO medium 102, thereby generating a periodically varying refractive index within the AO medium 102. As known in the art, this periodically varying refractive index is measured as a Bragg angle θ , which is measured for an acoustic wave incident on a first surface 102a of the AO medium 102. B 1 serves to diffract the laser light beam propagating within AO medium 102 (eg, propagating along beam path 114).

[0006] Diffraction of an incident laser light beam produces a diffraction pattern that typically includes zero-order and first-order diffraction peaks, and may also include higher order diffraction peaks (second order, third order, etc.). As known in the art, the zero-order diffraction peak portion of the diffracted laser light beam is referred to as the "zero-order" beam, and the first-order diffraction peak portion of the diffracted laser light beam is referred to as the "first order" beam. In general, the zero-order beam and the beams of other diffraction orders (e.g., first order beam, etc.) propagate along different beam paths upon exiting the AO medium 102 (e.g., through the second surface 102b of the AO medium 102 opposite the first surface 102a). For example, the zero-order beam propagates along the zero-order beam path, and the first-order beam propagates along the first-order beam path. The angle between the zero-order and the beam paths of the other diffraction orders (e.g., the angle θ between the zero-order beam path and the first-order beam path) may be determined by the angle between the zero-order and the beam paths of the other diffraction orders. D ) corresponds to a frequency (or frequencies) in the drive signal applied to diffract the laser light beam incident on the AO medium 102.

[0007] The amplitude of the applied drive signal (i.e., the amount of power in the applied drive signal) can nonlinearly affect the proportion of an incident laser light beam that is diffracted into various diffraction order beams, and the AOD can be driven to diffract a significant portion of the incident laser light beam into a first order beam and leave a relatively small portion of the incident laser light beam in other diffraction order beams (e.g., a zeroth order beam). In addition, the frequency of the applied drive signal can be rapidly changed to scan the first order beam (e.g., to facilitate processing different areas of a workpiece). Thus, AODs are advantageously incorporated into laser processing systems for use in the field of laser-based material processing to variably deflect the first order beam on a workpiece for processing (e.g., melting, vaporizing, ablation, marking, cracking, etc.) the workpiece.

[0008] Laser processing systems typically include one or more beam dumps to prevent laser light propagating along the zero-order beam path (and higher order beam paths) from reaching the workpiece. Thus, in a laser processing system, the first order beam path exiting the AOD 100 is typically deflected at an angle θ D The AOD 100 can be thought of as a beam path 114 that is rotated or deflected (by a distance of 100 mm) around the AOD 100. When the AOD 100 is driven to diffract an incident laser light beam, the axis about which the beam path 114 rotates (also referred to herein as the "axis of rotation") is orthogonal to the diffraction axis of the AOD 100 and the axis along which the incident laser light beam propagates within the AOD 100 (also referred to herein as the "optical axis"). The AOD 100 therefore deflects the incident beam path 114 within a plane (also referred to herein as the "deflection plane") that contains (or is substantially parallel to) the diffraction axis of the AOD 100 and the optical axis within the AOD 100. The spatial extent over which the AOD 100 can deflect the beam path 114 within the deflection plane is referred to herein as the "scan field" of the AOD 100.

[0009] The laser processing system may incorporate multiple AODs arranged in series to deflect the beam path 114 along two axes. For example, referring to FIG. 2, the first AOD 200 and the second AOD 202 may be arranged such that their respective diffraction axes (i.e., the first diffraction axis 200a and the second diffraction axis 202a, respectively) are perpendicular to each other. In this example, the first AOD 200 operates to rotate the beam path 114 about a first rotation axis 200b (e.g., orthogonal to the first diffraction axis 200a), thereby deflecting the incident beam path 114 in a first deflection plane (i.e., a plane that includes or is substantially parallel to the first diffraction axis 200a and the optical axis in the first AOD 200), where 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 a second axis of rotation 202b (e.g., orthogonal to the second diffraction axis 202a), thereby deflecting the incident beam path 114 in a second deflection plane (i.e., a plane that includes or is substantially parallel to the second diffraction axis 202a and the optical axis in the second AOD 202), where the second deflection plane is orthogonal to the second axis of rotation 202b. In view of the above, the first AOD 200 and the second AOD 202 may be collectively characterized as a multi-axis "beam positioner," each of which may be selectively operated to deflect the beam path 114 in the two-dimensional scan field 204. As can be appreciated, the two-dimensional range scan field 204 can be considered to be a superposition of two one-dimensional scan fields, i.e., 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.

[0010] Depending on the type of AOD included in the multi-axis beam positioner, it may be desirable to rotate the plane of polarization (i.e., the plane in which the electric field oscillates) of the light in the first beam path transmitted through the first AOD 200. Rotating the plane of polarization may be desirable if the amount of RF drive power required to diffract a significant portion of the incident laser light beam into the first beam depends strongly on the polarization state of the laser light beam being deflected. Furthermore, if each AOD of the multi-axis beam positioner includes an AO medium 102 formed of the same material, if each AOD uses the same type of acoustic waves (e.g. longitudinal mode acoustic waves) to deflect the incident laser light beam, and if it is desired to linearize the polarization state of the light in the first order beam transmitted through the first AOD 200 to a particular direction relative to the second diffraction axis 202a, it would be equally desirable to rotate the polarization state of the light in the first order beam transmitted through the second AOD 202 relative to the polarization state of the light in the first order beam transmitted through the first AOD 200 in the same way that the orientation of the second AOD 202 is rotated relative to the orientation of the first AOD 200. Thus, when the above conditions are met, some polarization rotation mechanism (not shown) would be located in the beam path 114 between the first and second AODs 200 to rotate the plane of polarization of the laser light beam output by the first AOD 200.

[0011] Those skilled in the art will recognize that the material forming the AO cells of the AOD may vary depending on the wavelength of the laser light beam diffracted therein. For laser light beams having wavelengths in the long wavelength infrared (LWIR) region of the electromagnetic spectrum (also referred to herein as "LWIR laser light beams"), the AO cells of the AOD are formed from crystalline germanium. Thus, if the AO cells of the first AOD 200 are formed from crystalline germanium, the plane of polarization of the laser light incident on the first AOD 200 should be parallel (or at least substantially parallel) to the first diffraction axis 200a, and also parallel (or at least substantially parallel) to the plane of polarization of the laser light output from the first AOD 200 (e.g., along the beam path 114). Similarly, if the AO cells of the second AOD 202 are formed from the same material as that of the first AOD 200 (i.e. crystalline germanium), then the plane of polarization of the laser light incident on the second AOD 202 should be parallel (or at least substantially parallel) to the second diffraction axis 202a, which is also parallel (or at least substantially parallel) to the plane of polarization of the laser light output from the second AOD 202 (e.g. along the beam path 114). For this reason, it may be desirable to rotate the plane of polarization of the laser light output from the first AOD 200 (e.g. along the beam path 114) to be parallel (or at least substantially parallel) to the first diffraction axis 200a and parallel (or at least substantially parallel) to the second diffraction axis 200b before it enters the second AOD 202.

[0012] In general, when the wavelength of the laser light beam is in the ultraviolet, visible or near infrared (NIR) region of the electromagnetic spectrum, polarization rotation can be easily achieved using a transmissive half-wave plate, as known in the art. The polarization direction for the incident laser light beam after passing through the half-wave plate is a function of the orientation of the half-wave plate with respect to the polarization direction of the incident laser light beam. However, when the wavelength of the laser light beam is a LWIR laser light beam, polarization rotation cannot be achieved using only a transmissive half-wave plate. Instead, one or more reflective phase retarding (RPR) mirrors and relay lenses can be used in various configurations to perform polarization rotation of the LWIR laser light beam propagating from the first AOD 200 to the second AOD 202. Although these configurations work well, the addition of mirrors and relay lenses increases the complexity and cost of a multi-axis beam positioner capable of deflecting a LWIR beam of laser light. Summary of the Invention

[0013] overview One embodiment may be broadly characterized as a multi-axis beam positioner capable of deflecting a beam path along a plurality of axes, the multi-axis beam positioner comprising a first acousto-optical (AO) deflector (AOD) and a second AOD arranged optically in series with each other, the first AOD arranged and configured to deflect the beam path along a first axis of the multi-axis beam positioner, the second AOD arranged and configured to deflect the beam path along a second axis of the multi-axis beam positioner, each of the first AOD and the second AOD having an AO cell and a transducer attached to the AO cell, the AO cell of the first AOD being formed from the same material as the AO cell of the second AOD, and the first AOD being configured differently from the second AOD.

[0014] Another embodiment may be broadly characterized as a multi-axis beam positioner capable of deflecting a beam path along a plurality of axes, the multi-axis beam positioner comprising a first acousto-optical (AO) deflector (AOD) and a second AOD arranged optically in series with each other, the first AOD arranged and configured to deflect the beam path along a first axis of the multi-axis beam positioner, the second AOD arranged and configured to deflect the beam path along a second axis of the multi-axis beam positioner, each of the first AOD and the second AOD having an AO cell and a transducer attached to the AO cell, the first AOD and the second AOD being longitudinal mode AODs, and there being no retarder between the first AOD and the second AOD.

[0015] Yet another embodiment may be broadly characterized as a multi-axis beam positioner comprising: an acousto-optical (AO) deflector (AOD) and a second AOD arranged optically in series with each other; and a heat exchanger coupled to the second AOD, wherein the first AOD is arranged and configured to deflect the beam path along a first axis of the multi-axis beam positioner and the second AOD is arranged and configured to deflect the beam path along a second axis of the multi-axis beam positioner, each of the first AOD and the second AOD having an AO cell and a transducer attached to the AO cell, the AO cell of the second AOD being formed from crystalline germanium, and the at least one heat exchanger configured to maintain the AO cell of the second AOD at a temperature lower than a temperature of the AO cell of the first AOD. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 shows a schematic of an acousto-optic deflector (AOD) and its operation.

[0017] [Diagram 2]FIG. 2 shows a schematic of a multi-axis beam positioner incorporating a pair of AODs arranged optically in series.

[0018] [Diagram 3] FIG. 3 illustrates a schematic of a multi-axis beam positioner according to an embodiment of the present invention. [Figure 4] FIG. 4 illustrates a schematic diagram of a multi-axis beam positioner according to an embodiment of the present invention.

[0019] [Diagram 5] FIG. 5 shows a graph of the measured thermal conductivity of germanium at low temperatures.

[0020] [Figure 6] FIG. 6 shows a graph of acoustic attenuation of longitudinal and shear waves in germanium at low temperatures. [Figure 7] FIG. 7 illustrates a schematic diagram of a multi-axis beam positioner according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Detailed Description Exemplary embodiments will now be described with reference to the accompanying drawings, in which, unless explicitly stated, the sizes, positions, etc. of components, features, elements, etc. and the distances therebetween are not necessarily to scale and have been exaggerated for ease of understanding.

[0022] The terms used in the specification are for the purpose of describing particular exemplary embodiments only and are not intended to be limiting. As used herein, the singular is intended to include the plural unless the content clearly indicates otherwise. Furthermore, it should be understood that the terms "comprises" and / or "comprising", when used herein, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise indicated, when a range of values ​​is described, the range includes the upper and lower limits as well as any subranges between the upper and lower limits of the range. Unless otherwise indicated, terms such as "first" and "second" are only used to distinguish elements from one another. For example, one node may be referred to as a "first node" and similarly another node may be referred to as a "second node" or vice versa. Section headings used herein, unless otherwise noted, are for organizational purposes only and should not be construed as limiting the subject matter described.

[0023] Unless otherwise indicated, "about," "around," "substantially," and the like mean that amounts, sizes, formulations, parameters, and other quantities and characteristics are not, and need not be, precise and may be approximate and / or larger or smaller, as appropriate or to reflect tolerances, conversion factors, rounding, measurement errors, and the like, as well as other factors known to those of ordinary skill in the art.

[0024] Spatially relative terms such as "below," "lower," "lower side," "upper," and "above" may be used herein for ease of description in describing the relationship of an element or feature to other elements or features as depicted in the figures. It should be understood that spatially relative terms are intended to include different orientations in addition to those depicted in the figures. For example, an element described as being "below" or "below" another element or feature would be oriented "above" the other element or feature if the object in the figure were inverted. Thus, the exemplary term "below" may include both an upward and downward orientation. If an object is oriented in another way (e.g., rotated 90 degrees or at another orientation), the spatially relative descriptors used herein may be interpreted accordingly.

[0025] Like numbers refer to like elements throughout the drawings, and thus the same or similar numbers may be described with reference to other drawings even if not mentioned or described in the corresponding drawing, and elements that are not numbered may be described with reference to other drawings.

[0026] It will be appreciated that many different forms and embodiments are possible without departing from the spirit and teachings of this disclosure, and that the disclosure should not be construed as limited to the example embodiments set forth herein, but rather, these examples and embodiments are provided so that this disclosure will be complete and all-inclusive, and will fully convey the scope of the disclosure to those skilled in the art.

[0027] Rather than using a relatively expensive and complicated arrangement of RPRs and relay lenses to rotate the plane of polarization between the AODs of a multi-axis beam positioner (capable of detecting LWIR laser light beams), embodiments of the present invention avoid the need for polarization rotation entirely by designing the first and second AODs differently from one another or by operating the first and second AODs differently from one another. Thus, a multi-axis beam positioner may be provided in which there are no RPRs or other transmissive waveplates (collectively referred to herein as "retarders") between the first and second AODs. In addition to simplifying the complexity of the beam path between the AODs, the elimination of the polarization rotation mechanism may allow the multi-axis beam positioner to be assembled faster and to be operated more reliably. Similarly, the elimination of the polarization rotation mechanism between the AODs may increase the overall optical transparency of the multi-axis beam positioner.

[0028] In the embodiments described below, each of the first AOD 200 and the second AOD 202 may be provided as a "longitudinal mode" or "isotropic" AOD, in which the incident and diffracted laser light beams pass through the same (or substantially the same) refractive index within the AO cell, and longitudinal acoustic waves propagate through the AO cell such that the polarization of the incident laser light beam is the same (or substantially the same) as the polarization of the diffracted laser light beam. Furthermore, in the embodiments described below, the AO cells of each of the first AOD 200 and the second AOD 202 are formed from crystalline germanium. As used herein, an AOD may be considered to be in a "parallel operating state" when the plane of polarization of the laser light incident on the AOD is parallel (or at least substantially parallel) to the diffraction axis of the AOD. Similarly, an AOD may be considered to be in a "perpendicular operating state" when the plane of polarization of the laser light incident on the AOD is perpendicular (or at least substantially perpendicular) to the diffraction axis of the AOD.

[0029] I. Embodiment 1 Referring to Fig. 3, a multi-axis beam positioner 300 according to an embodiment of the present invention includes a first AOD 200 and a second AOD 202 arranged optically in series as exemplarily described with respect to Fig. 2. As described above, the AO cells of the first AOD 200 and the second AOD 202 are formed from the same material (i.e., crystalline germanium). However, according to the present embodiment, the AO cells of each of the first AOD 200 and the second AOD 202 are cut and assembled into the respective AODs such that the diffraction axis of the AOD is parallel (or at least substantially parallel) to the 0111 crystal axis of the AO cell. Furthermore, the dimensions of the AO cells of the first AOD 200 and the second AOD 202 are identical (or at least substantially identical).

[0030] The first AOD 200 includes a plurality of first transducers 302 (e.g., two transducers as shown, or more than two transducers) attached at their transducer ends to the AO cell of the first AOD 200. Similarly, the second AOD 202 includes a plurality of second transducers (e.g., two or more transducers) attached at their transducer ends to the AO cell of the second AOD 202. In general, the transducers typically attached to any AO cell are positioned such that acoustic waves generated by adjacent transducers overlap each other within the AO cell. The transducers of the AOD are electrically connected to an RF power source (e.g., driver 304) by one or more RF power lines. For example, the plurality of first transducers (e.g., transducer 302) are electrically connected to the driver 304 by a common first RF power line 306a, and the plurality of second transducers are electrically connected to the driver 304 by a common second RF power line 306b.

[0031] In the illustrated embodiment, the RF driver 304 is operable to output the same or different RF signals (e.g., in terms of frequency, power, etc., or a combination thereof) to the first RF power line 306a and the second RF power line 306b. Thus, it is contemplated that during operation of the multi-axis beam positioner 300, the RF signals output to the first RF power line 306a and the second RF power line 306b may be the same as one another or different from one another. However, in other embodiments, the first RF power line 306a and the second RF power line 306b may be electrically connected to different RF power sources (i.e., different drivers).

[0032] In the illustrated embodiment, the multiple transducers mounted on a common AO cell are all electrically connected to a common RF power line. However, in other embodiments, two or more of the multiple transducers may be electrically connected to different RF power lines. Also, at least two of the different RF power lines may be electrically connected to the same RF power source or to different RF power sources (i.e., to the same driver or to different drivers).

[0033] Unlike the multi-axis beam positioner described above with respect to FIG. 2, the multi-axis beam positioner 300 does not include a mechanism disposed in the beam path 114 between the first AOD 200 and the second AOD 202 for rotating the plane of polarization of the laser light beam output by the first AOD 200. Rather, one of the first AOD 200 and the second AOD 202 is provided in a parallel operating state, and the other of the first AOD 200 and the second AOD 202 is provided in a perpendicular operating state. With the above-described AO cell materials and configurations, an RF signal having a relatively low power can be applied to the converter 302 of the AOD provided in the parallel operating state to cause the AOD to diffract the LWIR laser beam with a relatively high diffraction efficiency. However, an RF signal having a relatively high power must be applied to the converter 302 of the AOD provided in the perpendicular operating state to cause the AOD to diffract the LWIR laser beam with a similarly high diffraction efficiency.

[0034] For ease of discussion, the amount of power in the applied RF signal that will cause the AOD to diffract the laser beam with a desirably high diffraction efficiency is referred to herein as the "effective power," which may be equal (or nearly equal) to the saturated power AOD (i.e., the amount of power required to achieve maximum diffraction efficiency). Thus, to achieve a desired diffraction efficiency (e.g., greater than or equal to 95%), the effective power of the RF signal applied to the transducer of an AOD provided in a parallel operating state will generally be lower than the effective power of the RF signal applied to the transducer of an AOD provided in a perpendicular operating state.

[0035] Thus, in the context of the embodiment shown in Fig. 3, the first AOD 200 is provided in a parallel operating state and the second AOD 202 is provided in a perpendicular operating state. In this case, the double arrow 308 in the beam path 114 represents the polarization plane of the laser light beam propagating along the beam path 114. As exemplarily shown, the polarization plane of the laser light beam incident on each AOD is parallel (or substantially parallel) to the polarization plane of the laser light beam output from the AOD along the beam path 114. Furthermore, the polarization plane 308 is parallel (or substantially parallel) to the first diffraction axis 200a of the first AOD 200 and perpendicular (or substantially perpendicular) to the second diffraction axis 202a of the second AOD 202. In this example, an RF signal having a relatively low effective power (e.g., a first effective power) may be applied to each of the transducers 302 of the first AOD 200 to cause the first AOD 200 to diffract the LWIR laser beam with a relatively high diffraction efficiency (e.g., a first diffraction efficiency). However, an RF signal having a relatively high effective power (e.g., a second effective power) must be applied to each of the transducers of the second AOD 202 to cause the second AOD 202 to diffract the LWIR laser beam with a second diffraction efficiency that is equal (or approximately equal) to the first diffraction efficiency. For example, a desired diffraction efficiency (e.g., 95% or greater) could be obtained from the first AOD 200 by applying an RF signal having a first effective power of ~65 W to each transducer of the first AOD 200 (resulting in an RF power of ~130 W applied to the first AOD 200), and a similarly high diffraction efficiency could be obtained from the second AOD 202 by applying an RF signal having a second effective power in the range of 4 to 20 times the first effective power to each transducer of the second AOD 202 (resulting in an RF power of ~260 W to ~1300 W applied to the second AOD 202).

[0036] II. Embodiment 2 When an RF signal having a power level comparable to the second effective power described above is applied to the transducer of the AOD (i.e., in embodiment 1), it is possible that an undesirably large amount of heat (enough to damage the AOD) may be generated. To avoid or minimize the deleterious effects of this heat problem, heat may be extracted from the AOD (e.g., the second AOD 202 as shown in FIG. 3) in the multi-axis beam positioner 300 provided in a vertical operating state using a cooling jacket or other suitable or known heat exchange mechanism.

[0037] 4, a multi-axis beam positioner 400 according to another embodiment of the present invention may be provided in the same form as described above with respect to multi-axis beam positioner 300, but further includes a cooling jacket 402 in thermal contact with the second AOD 202 (there is no cooling jacket in thermal contact with the first AOD 200). Generally, assuming that the multi-axis beam positioner 400 is located in an environment having an ambient temperature of "room temperature" (e.g., at or about 293 K), the cooling jacket is configured to cool the AO crystal of the second AOD 202 to a temperature of 273.15 K or less.

[0038] It should be appreciated by those skilled in the art that optical grade crystalline germanium increases in thermal conductivity when cooled below 273.15K, achieving the highest thermal conductivity in the temperature range between 10K (or thereabouts) and 50K (or thereabouts), and then decreases appreciably when cooled further below 10K. See, for example, FIG. 5, which shows the thermal conductivity of germanium measured at low temperatures. It should also be appreciated by those skilled in the art that crystalline germanium is poor at absorbing longitudinal acoustic waves having ultrasonic frequencies at temperatures below 293K, and relatively low acoustic attenuation is obtained at temperatures below 100K (or thereabouts). See, for example, FIG. 6, which shows the acoustic attenuation of longitudinal and shear acoustic waves in germanium at low temperatures. The graphs shown in FIGS. 5 and 6 were taken from DR Suhre, "Multi-Stage Acousto-Optic Modulator," Proc. SPIE 0999, Laser Radar III, (February 18, 1989). In view of the above, the cooling jacket 402 may be configured in any known or suitable manner to cool the second AOD 202 to a temperature significantly below 293K, such as to a temperature of 250K or less, 200K or less, 150K or less, 100K or less, 50K or less, 10K (or thereabouts), etc., or a value between any of these values ​​(e.g., a temperature between 77K (or thereabouts) and 273.15K (or thereabouts)). In view of the above, the cooling jacket 402 may be generally characterized as including a metal sheath or casing having one or more fluid channels defined therein. As known in the art, each fluid channel communicates with one or more inlet and outlet ports that allow a cooling fluid (e.g., liquid nitrogen, fluid helium, or other known or suitable coolant) to be passed therethrough and pumped therethrough. If necessary, a dehumidifier (not shown) may be provided to prevent moisture in the atmosphere surrounding the second AOD 202 from condensing on optical surfaces of the second AOD 202 (e.g., corresponding to the first surface 102a and / or the second surface 102b described above with respect to FIG. 1).

[0039] Although the multi-axis beam positioner 400 has been described above as including a cooling jacket 402 configured to cool the AO cell of the second AOD 202 as described above, it will be appreciated that if the first AOD 200 is provided in a parallel operating state, a cooling jacket may similarly be provided to cool the AO cell of the first AOD 200.

[0040] III. Embodiment 3 7, a multi-axis beam positioner 700 according to another embodiment of the present invention may be provided in a similar manner as described above with respect to multi-axis beam positioner 300, but with the interaction length of an AOD provided in a perpendicular orientation state (i.e., second AOD 202 shown in FIG. 3) increased to be longer than the interaction length of an AOD provided in a parallel orientation state (i.e., first AOD 200 shown in FIG. 3). As used herein, the "interaction length" of an AOD refers to the width of an acoustic wave that can propagate through an AO cell of the AOD (measured along an axis passing through the AO cell perpendicular to (or passing through) the first and second surfaces 102a, 102b, along the direction indicated by the double arrow labeled "interaction direction").

[0041] Thus, the AO cell of the second AOD702 shown in Figure 7 is formed from the same material as the AO cell of the first AOD 200, and is cut and assembled into the second AOD702 such that the diffraction axis of the second AOD702 is parallel (or at least substantially parallel) to the AO cell's

[0111] crystal axis. However, the length of the AO cell of the second AOD702, measured along the direction indicated by the double arrow labeled "interaction direction", is longer than the length of the AO cell of the first AOD 200. Furthermore, the second AOD702 may include more transducers attached to its AO cell (e.g., arranged linearly in a pattern extending along the interaction direction) than the first AOD 200.

[0042] According to an embodiment of the invention, the interaction length of an AOD provided in a perpendicular orientation (also referred to herein as "Lperp") is at least 1.5 times longer than the interaction length of an AOD provided in a parallel orientation (also referred to herein as "Lpara"), i.e., Lperp=n*Lpara, where n is 1.5 or greater (e.g., n can be 1.5, 2, 2.5, 3, 4, 5, 10, 15, 20, 30, etc., or any value between these values). In one embodiment, Lpara is in the range of 17 mm to 19 mm.

[0043] By increasing the interaction length of the AOD provided in the vertical orientation, the effective power in the RF signal applied to each transducer of that AOD can be reduced while still obtaining a desirably high diffraction efficiency from the AOD. Thus, assuming that a desired diffraction efficiency (e.g., 95% or greater) can be obtained from the second AOD 202 by applying an RF signal having a second effective power to each transducer of the second AOD 202 in the multi-axis beam positioner 300, a similarly high diffraction efficiency can be obtained from the second AOD 702 by applying an RF signal having a third effective power to each transducer of the second AOD 702. In this case, the third effective power is generally significantly less than the second effective power.

[0044] In modifying the second AOD 202 to obtain a second AOD 702 with an increased interaction length, the amount of energy in the LWIR beam (also referred to herein as "optical energy") absorbed by the AO cell is also increased. The increased absorption of optical energy may result in heat or temperature gradients within the AO cell. This may damage the AOD or inhibit accurate / repeatable beam positioning by the AOD. To avoid or minimize the deleterious effects of this heating issue, heat may be extracted from the AOD provided in the vertical operating state using a cooling jacket or other suitable or known heat exchange mechanism.

[0045] For example, the multi-axis beam positioner 700 may optionally include a cooling jacket in thermal contact with the second AOD 702. Generally, assuming that the multi-axis beam positioner 400 is located in an environment having an ambient temperature of "room temperature" (e.g., at or about 293 K), the cooling jacket is configured to cool the AO crystal of the second AOD 702 by an amount that corresponds at least in part to an interaction length of the second AOD 702 (e.g., relative to the interaction length of the second AOD 202). For example, if the AO cell of the second AOD702 absorbs twice the amount of light energy as the AO cell of the second AOD202 (e.g., as a result of an increased interaction length of the second AOD702 relative to the interaction length of the first AOD202), then assuming the second AOD702 is placed in an environment having an ambient temperature of "room temperature", the cooling jacket may be configured to cool the AO cell of the second AOD702 by 20 K (or thereabouts), i.e., to a temperature in the range of 273 K (or thereabouts) to 278 K (or thereabouts).

[0046] Although the multi-axis beam positioner 700 has been described above as including a second AOD 702 having an increased interaction length (relative to the second AOD 202 shown in FIG. 3), it will be appreciated that the first AOD 200 of the multi-axis beam positioner 700 may similarly be modified to have an increased interaction length (e.g., relative to the first AOD 200 shown in FIG. 3). Similarly, a cooling jacket may similarly be provided to cool the AO cell of the first AOD 200 to compensate for thermal effects resulting from the increased interaction length.

[0047] IV. Embodiment 4 As used herein, an AOD in which a crystalline germanium AO cell is cut and assembled such that the

[0111] crystal axis of the AO cell is parallel or perpendicular (or at least substantially parallel or perpendicular) to the diffraction axis of the AOD is referred to herein as a "

[0111] oriented AOD." Similarly, an AOD in which a crystalline germanium AO cell is cut and assembled such that the

[0100] crystal axis of the AO cell is parallel or perpendicular (or at least substantially parallel or perpendicular) to the diffraction axis of the AOD is referred to herein as a "

[0100] oriented AOD." A multi-axis beam positioner according to yet another embodiment of the present invention may be provided by any of the methods described in any of the above embodiments, but the AO cell of the AOD provided in the vertical operating state is a

[0100] oriented AOD.

[0048] When driven with the same RF power, a 0100 AOD provided in a vertical operating state may be operated with a higher diffraction efficiency than an otherwise equivalent 0111 AOD provided in a vertical operating state. Thus, when the second AOD 202 shown in FIG. 3 is modified to be provided as a 0100 AOD, the modified second AOD 202 may be operated at a lower effective power than the second effective power to achieve a second diffraction efficiency equal (or nearly equal) to the first diffraction efficiency. When the second AOD 202 shown in FIG. 4 is modified to be provided as a 0100 AOD, the temperature to which the AO cell of the modified second AOD 202 must be cooled may be increased. In some cases, when the second AOD 702 shown in FIG. 7 is modified to be provided as a 0100 AOD, it may not be necessary to increase the interaction length of the modified second AOD 702 to the extent discussed in FIG. 7 above.

[0049] V. Additional Embodiments Although the second AOD in any of the above-described embodiments has been described as being provided as an AOD in a

[0100] orientation, the first AOD in any of the above-described embodiments may likewise be provided as an AOD in a

[0100] orientation. Thus, either or both of the first and second AODs in any of the above-described embodiments may be provided as AODs in a

[0100] orientation.

[0050] In general, the first and second AODs of the above-described embodiments are spaced apart from each other by a distance that is significantly greater than the wavelength of light in the diffractable laser light beam. However, in other embodiments, the first and second AODs of any of the above-described embodiments may be spaced apart from each other by a distance that is equal to or less than the wavelength of light in the laser light beam. In this sense, the first and second AODs may, for example, be considered to be "in optical contact" with each other. The first and second AODs may be in optical contact with each other by any known or other suitable method. For example, the first and second AODs may be in optical contact with each other by bonding the first AOD to the second AOD by a frit bonding process, a diffusion bonding process, or a similar process. In other examples, the first and second AODs may be in optical contact with each other by polishing, cleaning, and physically contacting the surfaces of the first and second AODs. Alternatively or in addition to the techniques described above, other optical contacting techniques can be used, such as solution assisted direct bonding, chemically activated direct bonding, or any combination thereof. In another example, the first and second AODs may be in optical contact by clamping the AODs together.

[0051] Additionally, although the embodiments described above describe the AO cells of each of the first AOD 200 and the second AOD 202 as being formed from crystalline germanium, the AO cells of each of the first AOD 200 and the second AOD 202 may be formed from other materials used in longitudinal mode AODs (e.g., quartz, fused silica, LiNbO 3It will be appreciated that the insulating layer 11 may be formed from a material other than silicon (e.g., GaAs).

[0052] VI. Conclusion The above is a description of the embodiments and examples of the present invention, and should not be construed as being limiting thereto. Although some specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily recognize that many modifications to the disclosed embodiments and examples and other embodiments are possible without significantly departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the claims. For example, those skilled in the art will understand that the subject matter of any sentence, paragraph, example, or embodiment can be combined with any or all of the subject matter of any other sentence, paragraph, example, or embodiment, unless such combinations are mutually exclusive. Thus, the scope of the present invention should be determined by the following claims and the equivalents of such claims to be included therein.

Claims

1. A multi-axis beam positioner capable of deflecting a beam path along a plurality of axes, comprising: a first acousto-optic (AO) deflector (AOD) and a second AOD arranged optically in series with each other; the first AOD is positioned and configured to deflect the beam path along a first axis of the multi-axis beam positioner; the second AOD is positioned and configured to deflect the beam path along a second axis of the multi-axis beam positioner; each of the first AOD and the second AOD includes an AO cell and a converter attached to the AO cell; the AO cell of the first AOD is formed from the same material as the AO cell of the second AOD; the first AOD is configured to be different from the second AOD; Multi-axis beam positioner.

2. A multi-axis beam positioner capable of deflecting a beam path along a plurality of axes, comprising: a first acousto-optic (AO) deflector (AOD) and a second AOD arranged optically in series with each other; the first AOD is positioned and configured to deflect the beam path along a first axis of the multi-axis beam positioner; the second AOD is positioned and configured to deflect the beam path along a second axis of the multi-axis beam positioner; the first AOD and the second AOD are longitudinal mode AODs; There is no retarder between the first AOD and the second AOD. Multi-axis beam positioner.

3. the AO cell of the first AOD is formed from the same material as the AO cell of the second AOD; a diffraction axis of the first AOD is at least substantially parallel to a first crystal axis of the material from which the AO cell of the first AOD is formed; and a diffraction axis of the second AOD is at least substantially perpendicular to the first crystal axis of the material from which the AO cell of the second AOD is formed; 3. The beam positioner according to claim 1 or 2.

4. 3. The beam positioner of claim 1, wherein the first AOD and the second AOD each include an AO cell formed from crystalline germanium.

5. The beam positioner of claim 4 , wherein a diffraction axis of the first AOD is at least substantially parallel to a [111] crystal axis of the AO cell of the first AOD.

6. The beam positioner of claim 5 , wherein a diffraction axis of the first AOD is at least substantially perpendicular to a [111] crystal axis of the AO cell of the first AOD.

7. the AO cell of the first AOD is formed from the same material as the AO cell of the second AOD; a diffraction axis of the first AOD is at least substantially parallel to a first crystal axis of the material from which the AO cell of the first AOD is formed; and a diffraction axis of the second AOD is at least substantially perpendicular to a second crystal axis of the material from which the AO cell of the second AOD is formed; 3. The beam positioner according to claim 1 or 2.

8. 3. The beam positioner of claim 1, wherein the diffraction axis of the second AOD is at least substantially parallel to the [100] crystal axis of the AO cell of the second AOD.

9. 3. The beam positioner of claim 1, further comprising a heat exchange mechanism thermally coupled to the second AOD, the heat exchange mechanism being capable of removing heat from the second AOD.

10. 10. The beam positioner of claim 9, wherein the heat exchange mechanism is capable of cooling the AO cell of the second AOD to a temperature of 250K or less.

11. 11. The beam positioner of claim 10, wherein the temperature is 200K or less.

12. 11. The beam positioner of claim 10, wherein the temperature is 10K or higher.

13. 3. The beam positioner of claim 1, further comprising a dehumidifier capable of preventing ambient moisture from condensing on at least one optical surface selected from the group consisting of the first AOD and the second AOD.

14. 3. The beam positioner of claim 1, wherein the interaction length of the second AOD is the same as the interaction length of the first AOD.

15. 3. The beam positioner of claim 1, wherein an interaction length of the second AOD is different from an interaction length of the first AOD.

16. 3. A beam positioner as described in claim 1 or 2, wherein the AO cell of the first AOD is in optical contact with the AO cell of the second AOD such that the optically contacting surfaces of the AO cells of the first AOD and the second AOD are separated by a distance that is less than or equal to the wavelength of light diffractable by the first AOD and the second AOD.

17. 1. A multi-axis beam positioner, comprising: a first acousto-optic (AO) deflector (AOD) and a second AOD arranged optically in series with each other; at least one heat exchanger coupled to the second AOD; Equipped with the first AOD is positioned and configured to deflect a beam path along a first axis of the multi-axis beam positioner; the second AOD is positioned and configured to deflect the beam path along a second axis of the multi-axis beam positioner; each of the first AOD and the second AOD includes an AO cell and a converter attached to the AO cell; the AO cell of the second AOD is formed from crystalline germanium; the at least one heat exchanger is configured to maintain the AO cells of the second AOD at a temperature lower than a temperature of the AO cells of the first AOD. Multi-axis beam positioner.

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