PEM support systems and methods

Abstract

Apparatus include an elastically deformable photoelastic modulator (PEM) assembly holder defining an interior volume sized to receive at least one transducer of a PEM assembly, wherein the PEM assembly includes the at least one transducer and a photoelastic optical element attached to the at least one transducer and wherein the at least one transducer has a plurality of holder contact surfaces, wherein the PEM assembly holder includes a plurality of receiving portions located on side walls facing the interior volume and corresponding to respective ones of the holder contact surfaces of the at least one transducer, each receiving portion being displaceable through deformation of the PEM assembly holder so that the at least one transducer is insertable in the interior volume and cushionably supported in a predetermined position with the receiving portions in contact with the respective holder contact surfaces and such that the photoelastic optical element does not contact the PEM assembly holder.

Description

[0001] PEM SUPPORT SYSTEMS AND METHODS

[0002] FIELD

[0003] This application relates to photoelastic modulator support systems and methods.

[0004] BACKGROUND

[0005] Photoelastic modulators (PEMs) have many applications across industries and research areas, and their uses are increasing over time. For high-quality performance, a PEM should generally perform efficiently, with a large portion of supplied power being converted to resonant vibration. However, efficient operation of a PEM can be complex and involve various tradeoffs. Accordingly, a need remains for further improvements to PEM support systems and methods.

[0006] SUMMARY

[0007] According to an aspect of the disclosed technology, apparatus can include an elastically deformable photoelastic modulator (PEM) assembly holder defining an interior volume sized to receive at least one transducer of a PEM assembly, wherein the PEM assembly includes the at least one transducer and a photoelastic optical element attached to the at least one transducer and wherein the at least one transducer has a plurality of holder contact surfaces, wherein the PEM assembly holder includes a plurality of receiving portions located on side walls facing the interior volume and corresponding to respective ones of the holder contact surfaces of the at least one transducer, each receiving portion being displaceable through deformation of the PEM assembly holder so that the at least one transducer is insertable in the interior volume and cushionably supported in a predetermined position with the receiving portions in contact with the respective holder contact surfaces and such that the photoelastic optical element does not contact the PEM assembly holder. Some examples further include the PEM assembly with the at least one transducer inserted in the interior volume and secured in the cushionably supported predetermined position by the PEM assembly holder, and with the photoelastic optical element attached to the at least one transducer. In some examples, the at least one transducer comprises two transducers attached to the photoelastic optical element. In some examples, the two transducers extend along respective modulation axes extending through a center of the photoelastic optical element and arranged at 45 degrees with respect to each other such that the PEM assembly forms a dual PEM assembly. In some examples, the PEM assembly holder comprises a first portion configured to hold the one of the two transducers and second portion configured to hold the other of the two transducers, wherein the first portion and second portion are spaced apart and disconnected from each other. In some examples, the at least one transducer attached to the photoelastic optical element is configured to modulate a birefringence of the photoelastic optical element. Some examples further include a rigid housing having an interior region configured to receive and support the PEM assembly holder holding the PEM assembly. Some examples further include a lid configured to cover the rigid housing and to compress the PEM assembly holder as the cover is secured to the rigid housing. In some examples, the PEM assembly holder is sized in relation to the rigid housing such that the compression achieved through securing the lid to the rigid housing varies a holding force of the at least one transducer by the PEM assembly holder. In some examples, the variable holding force is configured to vary a vibration efficiency of the PEM assembly. In some examples, the rigid housing includes a plurality of interior support sidewalls corresponding to a plurality of exterior sidewalls of the PEM assembly holder. In some examples, the holder contact surfaces are on tapered protrusions extending outward from opposite faces of the at least one transducer and the receiving portions include indentations shaped to receive the tapered protrusions. In some examples, the PEM assembly holder includes a through cavity configured to provide a shielded path for a shielded or unshielded transducer cable coupled to an outward face of the at least one transducer through the PEM assembly holder to an interior transducer cable port. In some examples, the PEM assembly holder has a Shore A durometer hardness of less than or equal to 80.

[0008] According to a further aspect of the disclosed technology, methods can include providing a photoelastic modulator (PEM) assembly comprising at least one transducer having a plurality of holder contact surfaces and a photoelastic optical element attached to the at least one transducer, and inserting the at least one transducer of the PEM assembly in an interior volume of an elastically deformable PEM assembly holder having a plurality of receiving portions adjacent to the interior volume and respectively corresponding to the holder contact surfaces, wherein the inserting includes elastically displacing at least one of the receiving portions so that the receiving portions contact the respective holder contact surfaces and the at least one transducer becomes held by the PEM assembly holder so that the PEM assembly is cushionably supported and held in a predetermined position through the at least one transducer with the photoelastic optical element not in contact with the PEM assembly holder. Some examples further include inserting the PEM assembly holder in an interior region of a rigid PEM housing having one or more interior supporting sidewalls dimensioned to correspond with one or more exterior elastic sidewalls of the PEM assembly holder. In some examples, the inserting the at least one transducer comprises inserting the two transducers into two separate spaced apart portions of the PEM assembly holder. In some examples, the inserting the at least one transducer includes routing a shielded or unshielded transducer cable coupled to an outward face of the at least one transducer, along a path through a cavity of the PEM assembly holder to allow access by the cable to an interior transducer cable port. Some examples further include covering the rigid PEM housing with a lid thereby compressing the PEM assembly holder such that the compression achieved through securing the lid to the rigid housing varies a holding force of the at least one transducer by the PEM assembly holder. In some examples, the covering comprises adjusting the variable holding force to vary a vibration efficiency of the PEM assembly by a selected amount.

[0009] The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 A is a top view of an example photoelastic modulator (PEM) assembly supported by a PEM assembly holder.

[0012] FIG. IB is a side view of the apparatus of FIG. 1 A and also including a cross-section of an enclosure.

[0013] FIG. 2A is a plan view of a dual-PEM assembly.

[0014] FIG. 2B and 2C are side cross-sectional views of the plan view of FIG. 2A.

[0015] FIG. 2D is a plan view of the dual-PEM similar to that shown in FIG. 2A but without internal components being shown.

[0016] FIG. 2E is a side cross-section view of the dual-PEM shown in FIG. 2D.

[0017] FIG. 2F is a perspective view of the dual-PEM example without a lid being installed.

[0018] FIG. 2G is a perspective detailed view of a portion of the dual-PEM shown in FIGS. 2A-2F. FIGS. 3A-3C are images of an example dual-PEM.

[0019] DETAILED DESCRIPTION

[0020] Introduction

[0021] A photoelastic modulator (“PEM”) is an optical device that is used for modulating the polarization of a beam of light. A PEM employs the photoelastic effect as a principle of operation. The term "photoelastic effect" means that an optical element that is mechanically stressed and strained (deformed) exhibits birefringence that is proportional to the amount of deformation induced into the element. Birefringence means that the refractive index of the optical element is different for different components of a beam of polarized light that propagates through the optical element. A PEM includes an optical element, such as fused silica, that has attached to it a transducer for vibrating the optical element. The transducer typically vibrates at a fixed frequency within, for example, the low-frequency, ultrasound range of about 20 kHz to 100 kHz, and in some examples, higher frequencies. The mass of the element is compressed and extended along an axis of the optical element as a result of the vibration. The combination of the optical element and the attached transducer may be referred to as an optical assembly or PEM assembly. The axis along which the optical element vibrates is referred to as the optical axis or modulation axis of the PEM.

[0022] The optical assembly is mounted within a housing or enclosure that normally includes apertures through which the light to be modulated is directed through the optical element in a direction generally perpendicular to the optical axis of the PEM. The housing supports the optical assembly in a manner that permits the optical element to be driven (vibrated) within it to achieve the above-noted photoelastic effect while at the same time holding the PEM in place.

[0023] PEMs are commonly used in measuring polarization properties of either a light beam or a sample. Many instruments use two or more PEMs to provide measurements of certain polarization properties. When two PEMs are used in a single instrument, they are typically arranged so that their optical axes are oriented to be 45 degrees apart (as considered in a direction perpendicular to those two optical axes). Examples of typical, two-PEM instruments include complete Stokes polarimeters, Tokomak polarimeters, and several other polarimeters and ellipsometers. In particular examples herein, dual PEMs are also described in which a plurality of transducers (often two) are attached to a single optical element, often at 45 degree relation.

[0024] In the past, the mechanism for holding the optical element in the housing of the PEM used rigid barrel supports with grommet extensions to contact surfaces of the optical element. The rigid supports required additional machining steps and the grommets added parts and complexity to installation. Moreover, it has been found that the existing mechanism can have performance limitations. The resonant frequency and oscillation efficiency are sensitive to any mechanical coupling to the PEM housing so that an increase of such mechanical coupling decreases oscillation efficiency and absolute retardation and destabilizes resonant frequency. By decreasing post support rigidity, driving voltage for the PEM and / or power requirements can be significantly reduced. For instance, in some embodiments, the driving voltage can be reduced a third and power requirements by half. Further approaches for holding PEMs involve those disclosed in U.S. Patent No. 11,307,438 (incorporated herein by reference).

[0025] Single Transducer Example FIGS. 1 A-1B shows a photoelastic modulator (PEM) assembly 100 that can be supported by a PEM assembly holder 102 made of an elastically deformable material. The PEM assembly 102 includes at least one transducer 104 and a photoelastic optical element 106 that is attached to the at least one transducer at an end 108. Wires (not shown) can be coupled to opposite faces 110, 112 of the transducer to cause the transducer to vibrate along with the attached photoelastic optical element 106 along a modulation axis 114.

[0026] The transducer 104 includes holder contact surfaces 116, 1 18 that are shaped to correspond with receiving portions 120, 122 of the PEM assembly holder 102. For example, contact surface 116 can correspond to a protrusion on the transducer 104 and the receiving portion 120 can correspond to an indent in the PEM assembly holder 102. Similarly, the contact surface 118 can correspond to a separate protrusion on the transducer 104 and the receiving portion 122 can correspond to a separate indent in the PEM assembly holder 102 (more clearly seen in FIG. I B).

[0027] The PEM assembly holder 102 can define an interior volume 124 in which the transducer 104 can be inserted, e.g., through an opening 126. With the elasticity of the PEM assembly holder 102, one or more of its sides can be flexibly displaced so that the transducer end of the PEM assembly 100 can be inserted into the interior volume 124. The transducer 104 can slide into a detent- like secure position where the holder contact surfaces 116, 118 are mated with the respective receiving portions 120, 122. In such a position, the photoelastic optical element 106 can avoid any contact with the PEM assembly holder 102.

[0028] An enclosure 128 (omitted from FIG. 1A for clarity) can be sized to receive and enclose the PEM assembly holder 102 and PEM assembly 100. In particular, the enclosure 128 can be dimensioned to snugly hold the PEM assembly holder 102 without contacting the transducer 104 or photoelastic optical element 106 of the PEM assembly 100. For example, the enclosure 128 can contact multiple sides (directly or through intervening structural components) of the PEM assembly holder 102 to support the PEM assembly holder 102. This can allow the PEM assembly 100 to be firmly held in position, but also provide a large amount of free vibrational movement of the PEM assembly 100, and particularly the photoelastic optical element 106 which can, e.g., only contact the transducer through the attachment point and the surrounding gas in the enclosure. In some examples, the dimensions of the PEM assembly holder 102 relative to the enclosure 128 associated with the mating of the holder contact surfaces 116, 118 and respective receiving portions 120, 122 can be selected to allow an amount deflection by the PEM assembly holder 102 when the PEM assembly holder 102 is secured by the enclosure 128. For example, where the PEM assembly holder 102 is slightly larger in the vertical direction of FIG. IB, securing in the enclosure 128 can cause the PEM assembly holder to compress and increase a holding force on the transducer 104 and therefore on the PEM assembly 100.

[0029] Dual -Transducer PEM Example

[0030] FIGS. 2A-2G are an example of a dual-transducer PEM 200. The dual-transducer PEM 200 includes a PEM assembly 202 that can include first and second transducers 204a, 204b attached at respective ends to a photoelastic optical element 206. The PEM assembly 202 is suspended and held within a rigid housing 208 by an elastically deformable PEM assembly holder 210. The rigid housing 208 can be made a aluminum, steel, polymer, etc. The PEM assembly holder 210 can include two separate, spaced- apart elastically deformable sub-holders 212a, 212b each defining a respective interior volume 213a, 213b. In some examples, the PEM assembly holder 210 can be a single piece.

[0031] The PEM assembly holder 210 can be formed of a suitable extrusion printable resilient thermoplastic elastomer material. In other examples, the PEM assembly holder 210 can be injection molded or waterjetted. Any of the PEM assembly holders disclosed herein (e.g., the holder 102, holder 210) can be made of an extruded resilient material that is 3-D printed. Suitable material includes the “ninjaflex” brand thermoplastic elastomer filament material manufactured by NinjaTek Corporation. For applications involving high-vacuum environments where the use of materials with low-outgassing properties is required to reduce contamination from out-gassing, including space application, baked-out silicone or other suitable materials may be substituted as necessary. Typically, during 3-D printing, a continuous thread of thermoplastic material is delivered to an extrusion head that heats the material and delivers the heated material to a surface in a controlled manner. The heated material fuses with adjacent material as it is delivered to a stage and multiple passes are performed in a controlled manner so that a three-dimensional object is formed.

[0032] For instance, and using PEM assembly holder 210 as an example, a plurality of elastically deformable filaments are fused to adjacent filaments during the 3-D printing process to create striated structures that form the body (or bodies) of the PEM assembly holder 210. The adjacently fused filaments provide a resilience associated with flexure for the body of the PEM assembly holder in addition to the resilience associated with the thermoplastic material itself. The diameter of the filaments can vary from embodiment to embodiment, with smaller diameters typically increasing printing duration and providing higher resolution for complex shapes. Further, the in-fill percentage (fill density) and / or cross-section along the body of the PEM assembly holder can also vary. In this regard, and in certain embodiments of the disclosed technology, the surfaces of the PEM assembly holder (e.g., at the various walls that form the shape of the holder) are substantially continuous and have a high fill density (e.g., >90%, such as 100%) whereas the interior portion of walls of the PEM assembly holder can have a lower fill density (e.g., <90%, <50%, <20%, <10%), effectively creating a semi -hollow or substantially hollow structure. The fill density of the interior is typically referred to as the “in-fill percentage”. In some examples, in-fill percentages of about 5%, 10%, 15%, 25%, and 35% are used.

[0033] Each of the sub-holders 212a, 212b includes a set of receiving portions 214a, 214b, 216a, 216b that are shaped to receive and mate with respective holder contact surfaces 218a, 218b, 220a, 220b of the first and second transducers 204a, 204b. In many examples, holder contact surfaces 218a-220b can correspond to surfaces of rigid protrusions extending from the transducers 204a, 204b, and receiving portions 214a-216b can include indentations and surfaces defined by the indentations that are shaped to match or correspond with the protrusions. In further examples, receiving portions can be protrusions and holder contact surfaces can correspond to indented surfaces.

[0034] An example of mating between receiving portion 214a and holder contact surface 218a can be seen more clearly in perspective view FIG. 2G in which sub-holder 212a is made transparent while the transducer 204a and optical element 206 remain solid and the housing 208 is omitted 208 for clarity. As shown in FIG. 2G, a protrusion 222 includes a conical portion 224a and a cylindrical portion 224b, and an indentation 226 includes a conical portion 228a near an inside surface 230 of the sub-holder 212a and a cylindrical through-hole portion 228b extending to an outside surface 232 of the sub-holder 212a. When the holder contact surface 218a is mated with the receiving portion 214a, a frustum contact area 234 can be defined. It will be appreciated that various shapes and shape portions may be used for receiving portions and holder contact surfaces, including but not limited to notches, spherical, convex, concave, serrated, conical, frustoconical, cylindrical, square, and / or polygonal, etc.

[0035] The sub-holders 212a, 212b can be supportably situated in an interior volume 236 of the rigid housing 208, e.g., in cushionable contact (directly or through intermediate elements) one or more surfaces, such as a bottom surface 238 and side surfaces 240, 242, and back surface 243. With the sub-holders 212a, 212b situated in the rigid housing 208, the sub-holders 212a, 212b can be flexed open and the transducers 204a, 204b of PEM assembly 202 can be inserted into the interior volumes 213a, 213b. The transducers 204a, 204b can be inserted until the receiving portions 214a-216b are mated to holder contact surfaces 218a-220b and a detent-like securing of the PEM assembly 202 in a predetermined position is obtained. With the transducers 204a, 204b in the predetermined position, the PEM assembly 202 is cushionably suspended by the PEM assembly holder 210 in the rigid housing 208. In particular, the photoelastic optical element 206 can be suspended in a position where it is unsupported through direct contact with supports other than the attachment area between the photoelastic optical element 206 and the transducers 204a, 204b. In representative examples, the transducers 204a, 204b are arranged at 45 degrees with respect to each other. The arrangement can form dual cantilever support for the photoelastic optical element 206, each being approximately 22.5 to a main bisecting axis of the PEM 200. During operation the transducers 204a, 204b vibrate the photoelastic optical element 206 along respective modulation axes 244a, 244b that are at 45 degrees to each other. An incident beam propagating perpendicularly to the modulation axes 244a, 244b can pass through first window 246, through the photoelastic optical element 206 to become modulated, and through a second window 248. In some examples, the incident beam can pass through second window 248 and exit the first window 246. In representative dual-PEM examples, the dual-PEM can be configured to operate as a rotating waveplate and / or with a selectable modulation axis between 0 degrees and 45 degrees.

[0036] The rigid housing 208 can include a lid 250 that can enclose the PEM assembly 202 and PEM assembly holder 210. The first window 246 can correspond to an aperture in the lid 250. The lid 250 can be secured to a main body 252 of the rigid housing 208 with screws or other fasteners. In selected examples, with the lid 250 removed and the sub-holders 212a, 212b situated in their predetermined supporting position in the 236, a dimension of the sub-holders 212a, 212b between the bottom surface 238 and an inside surface 254 of the lid 250 can be slightly smaller than a similar dimension between bottom surfaces 256a, 256b and top surfaces 258a (232), 258b of the sub-holders 212a, 212b. Because of the difference and the elasticity of the sub-holders 212a, 212b, and the positioning of the receiving portions 214a-216b (e.g., parallel to this dimension), the securing of the lid 250 can also compressibly but cushionably secure sub-holders 212a, 212b against to the PEM assembly 202. The holding force of the transducers 204a, 204b can be varied by varying the compression of the lid 250 to the main body 252 (e.g., varying fastener torque). The variable compression can allow an operator to tune a broadening of an efficiency range of operational frequencies of the photoelastic optical element 206.

[0037] The sub-holders 212a, 212b can include respective holes or grooves 260a, 260b which can be situated to allow respective transducer cables 262a, 262b to pass through the holes or grooves 260a, 260b. In FIGS. 2A-2G, positions of cables 262a, 262b, 266a, 266b are shown schematically and not inserted through the respective holes or grooves 260a, 260b or attached to terminations 264a, 264b, 268a, 268b. As the PEM assembly 202 is inserted and installed in the sub-holders 212a, 212b, the cables 262a, 262b can be fed through the holes or grooves 260a, 260b. The cables 262a, 262b can be secured to cable terminations 264a, 264b at the back surface 243. Cables 266a, 266b can be secured to cable terminations 268a, 268b.

[0038] In some examples, cables 262a, 262b, 266a, 266b can be metal cables that are unshielded or unjacketed. For example, the holes or grooves 260a, 260b can allow the insertion of unshielded or unjacketed metal cables, which can be sized to the minimum gauge necessary to transfer the required electrical charge to the surfaces of the transducers, thereby minimizing any unintended physical mass or stiffness that would attenuate the resonant efficiency of the transducers, while simultaneously minimizing the risk that any unshielded wires will come in contact with any of the metal surfaces of the PEM 200, such as the housing 208, causing an unintended short in the electrical system. In this way, the PEM assembly holder 210 can provide not only a designated path for one or more of the cables coupled to the transducers, but also physical and electrical shielding for the system. In some examples, unshielded wires that are attached to either side of the transducers 204a, 204b can be sized to be the smallest gauge required to transfer the appropriate electrical charge to the transducer, through gold coatings applied to both surfaces. The small gauge and lack of shielding on this wire can minimize the attenuation of the cable on the natural resonance of the transducer. This attenuation effect is magnified if the wire comes in physical contact with the housing 208, since the wire will resonate / buzz at the same frequency as the transducer.

[0039] General Considerations

[0040] As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” does not exclude the presence of intermediate elements between the coupled items.

[0041] The systems, apparatus, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved. Any theories of operation are to facilitate explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation. Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. Additionally, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high- level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0042] As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” does not exclude the presence of intermediate elements between the coupled items.

[0043] The systems, apparatus, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved. Any theories of operation are to facilitate explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation.

[0044] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. Additionally, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high- level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0045] - to - In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are only representative examples and should not be taken as limiting the scope of the disclosure.

[0046] Alternatives specifically addressed in these sections are merely exemplary and do not constitute all possible alternatives to the embodiments described herein. For instance, various components of systems described herein may be combined in function and use. We therefore claim all that comes within the scope of the appended claims.

Claims

We claim:

1. An apparatus, comprising: an elastically deformable photoelastic modulator (PEM) assembly holder defining an interior volume sized to receive at least one transducer of a PEM assembly, wherein the PEM assembly includes the at least one transducer and a photoelastic optical element attached to the at least one transducer and wherein the at least one transducer has a plurality of holder contact surfaces; wherein the PEM assembly holder includes a plurality of receiving portions located on side walls facing the interior volume and corresponding to respective ones of the holder contact surfaces of the at least one transducer, each receiving portion being displaceable through deformation of the PEM assembly holder so that the at least one transducer is insertable in the interior volume and cushionably supported in a predetermined position with the receiving portions in contact with the respective holder contact surfaces and such that the photoelastic optical element does not contact the PEM assembly holder.

2. The apparatus of claim 1, further comprising the PEM assembly with the at least one transducer inserted in the interior volume and secured in the cushionably supported predetermined position by the PEM assembly holder, and with the photoelastic optical element attached to the at least one transducer.

3. The apparatus of claim 1 , wherein the at least one transducer comprises two transducers attached to the photoelastic optical element.

4. The apparatus of claim 3, wherein the two transducers extend along respective modulation axes extending through a center of the photoelastic optical element and arranged at 45 degrees with respect to each other such that the PEM assembly forms a dual PEM assembly.

5. The apparatus of claim 3, wherein the PEM assembly holder comprises a first portion configured to hold the one of the two transducers and second portion configured to hold the other of the two transducers, wherein the first portion and second portion are spaced apart and disconnected from each other.

6. The apparatus of claim 1 , wherein the at least one transducer attached to the photoelastic optical element is configured to modulate a birefringence of the photoelastic optical element.

7. The apparatus of claim 1 , further comprising a rigid housing having an interior region configured to receive and support the PEM assembly holder holding the PEM assembly.

8. The apparatus of claim 7, further comprising a lid configured to cover the rigid housing and to compress the PEM assembly holder as the cover is secured to the rigid housing.

9. The apparatus of claim 8, wherein the PEM assembly holder is sized in relation to the rigid housing such that the compression achieved through securing the lid to the rigid housing varies a holding force of the at least one transducer by the PEM assembly holder.

10. The apparatus of claim 9, wherein the variable holding force is configured to vary a vibration efficiency of the PEM assembly.

11. The apparatus of claim 7, wherein the rigid housing includes a plurality of interior support sidewalls corresponding to a plurality of exterior sidewalls of the PEM assembly holder.

12. The apparatus of claim 1, wherein the holder contact surfaces are on tapered protrusions extending outward from opposite faces of the at least one transducer and the receiving portions include indentations shaped to receive the tapered protrusions.

13. The apparatus of claim 1, wherein the PEM assembly holder includes a through cavity configured to provide a shielded path for a shielded or unshielded transducer cable coupled to an outward face of the at least one transducer through the PEM assembly holder to an interior transducer cable port.

14. The apparatus of claim 1 , wherein the PEM assembly holder has a Shore A durometer hardness of less than or equal to 80.

15. The apparatus of claim 1 , wherein the PEM assembly holder is made of a low- outgassing thermoplastic material configured to reduce contamination associated with outgassing.

16. A method, comprising: providing a photoelastic modulator (PEM) assembly comprising at least one transducer having a plurality of holder contact surfaces and a photoelastic optical element attached to the at least one transducer; and inserting the at least one transducer of the PEM assembly in an interior volume of an elastically deformable PEM assembly holder having a plurality of receiving portions adjacent to the interior volume and respectively corresponding to the holder contact surfaces, wherein the inserting includes elastically displacing at least one of the receiving portions so that the receiving portions contact the respective holder contact surfaces and the at least one transducer becomes held by the PEM assembly holder so that the PEM assembly is cushionably supported and held in a predetermined position through the at least one transducer with the photoelastic optical element not in contact with the PEM assembly holder.

17. The method of claim 16, further comprising, inserting the PEM assembly holder in an interior region of a rigid PEM housing having one or more interior supporting sidewalls dimensioned to correspond with one or more exterior elastic sidewalls of the PEM assembly holder.

18. The method of claim 16, wherein the inserting the at least one transducer comprises inserting two transducers into two separate spaced apart portions of the PEM assembly holder.

19. The method of claim 16, wherein the inserting the at least one transducer includes routing a shielded or unshielded transducer cable coupled to an outward face of the at least one transducer, along a path through a cavity of the PEM assembly holder to allow access by the cable to an interior transducer cable port.

20. The method of claim 17, further comprising, covering the rigid PEM housing with a lid thereby compressing the PEM assembly holder such that the compression achieved through securing the lid to the rigid housing varies a holding force of the at least one transducer by the PEM assembly holder.

21. The method of claim 20, wherein the covering comprises adjusting the variable holding force to vary a vibration efficiency of the PEM assembly by a selected amount.

Images