Prismatic-free differential interference contrast microscope with tunable beam shearing distance

Abstract

A pair of light rays spatially sheared at a controllable beam shearing distance is generated by a module having a beam splitter (BS) and two mirrors. The BS splits the input light into a first split light and a second split light propagating on a first light path and a second light path, respectively. The two reflectors are located at distal ends of the two light paths, respectively, and each split light is subjected to two-stage reflection, thereby generating a first reflected light and a second reflected light directed to the BS. The BS processes the two reflected rays to generate the pair of spatially sheared rays. The orientation of the two mirrors in the deflection angle, pitch angle, or both can be collectively adjusted to achieve and control the beam shear distance without the use of any birefringent crystal based prisms. The module is used to form a differential interferometric contrast (DIC) microscope that provides advantages of variable shear distance, orientation independence, and the like.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 63 / 593,540, filed on October 27, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0003] abbreviation

[0004] BS Beam Splitter

[0005] DIC Differential Interference Contrast

[0006] PBS Polarization Beam Splitter Technical Field

[0007] The present application relates generally to optical microscopy. In particular, the present application relates to a DIC microscope based on the generation of spatially or angularly sheared light rays without the use of any birefringent crystal-based prisms in such generation. Background Art

[0008] DIC microscopy is a widely used microscope for generating phase contrast images of weakly scattering samples. This technique utilizes the unique properties of birefringent crystals (such as Wollaston prisms and Nomarski prisms), which can split the incident light beam into two orthogonally polarized rays. These parallel rays are separated by a small spatial distance and interact with the sample before recombining in the imaging path. After passing through the analyzer, the combined light rays with the optical phase difference caused by the sample produce optical interference, which causes the thickness contrast of transparent samples. This technique can also be used to measure the surface morphology of opaque and reflective samples with accurate determination of beam shear distance. For example, see Chiu, H.C. (2019), “Measurement of beam shear angle of polarizing prisms beyond the diffraction limit using a positioning method,” Optics Communications, 435, 227-231; Zeng, Z. (2020), “Dual-beam shear differential interference microscopy for full-field surface deformation gradient characterization,” Journal of Mechanics and Physics of Solids, 145, 104-162; and Chan, K.H., Du, S., and Chen, X. (2022), “Subnanometer precision for surface characterization by reflected light differential interference microscopy,” Journal of Metrology Science and Technology, 34, 025-202.

[0009] It should be noted that the measurable range, lateral and axial resolution of planar topography characterization are sensitive to the value of the beam shear distance. On the one hand, the larger the shear distance, the higher the contrast shown in the image. On the other hand, the smaller the shear distance, the finer the details captured in the image. However, the shear distance of all DIC prisms is limited by the birefringence properties and geometry, thus limiting the optimization potential of the DIC prism.

[0010] Some techniques have been proposed to overcome the above problems. For example, the total shear distance can be increased by using two Nomarski prisms in combination, and / or the beam shear angle can be changed by adjusting the relative orientation between the prisms, thereby changing the beam shear distance. However, these approaches make the microscope system very complicated. In addition, the complex optical components are difficult to align. Therefore, the image quality is greatly affected. As disclosed in US 7,233,434 B2, two Nomarski prisms with liquid crystals can also be used to switch the shear direction electronically. However, the switching time for the shear direction is long and is limited by the liquid crystal.

[0011] In another approach, US 9,454,809 suggests achieving interference contrast by applying a phase mask in the Fourier plane of the microscope. This phase mask can be any diffractive optical element or a spatial light modulator. Variable shear distance and direction can be achieved by electronically changing this phase mask. However, this approach requires highly spatially coherent illumination, which may be difficult to achieve, and the cost of the spatial light modulator is high. Therefore, there is a need in the art for a more efficient and cost-effective solution for achieving variable shear distance and direction in DIC microscopy. Summary of the invention

[0012] A first aspect of the present disclosure is to provide a beam shear distance module for generating a first output light and a second output light from a first input light, wherein the first output light and the second output light are separated by a controllable beam shear distance.

[0013] The beam shear distance module includes a BS, a first reflector, and a second reflector. The BS is configured to split a first input light into a first split light and a second split light propagating on a first optical path and a second optical path, respectively. The first optical path and the second optical path define a reference vertical direction perpendicular to the first optical path and the second optical path. The first reflector and the second reflector are located at distal ends of the first optical path and the second optical path, respectively. The first reflector and the second reflector are oriented to cause each of the first split light and the second split light to undergo two-stage reflection, so that: (1) the first split light generates a first reflected light pointing to the BS and propagating along a first direction parallel to the second optical path; and (2) the second split light generates a second reflected light pointing to the BS and propagating along a second direction parallel to the first optical path. The first reflected light and the second reflected light are processed by the BS to generate a first output light and a second output light propagating along the first direction. In addition, the deflection angle, the pitch angle, or the orientation of both the first reflector and the second reflector relative to the reference vertical direction can be adjusted jointly (or jointly) to control the beam shear distance between the first output light and the second output light. Thus, advantageously, beam shear distance is achievable, controllable and tunable without the need to use any birefringent crystal based prisms in the beam shear distance module.

[0014] In some embodiments, the BS is implemented by a flat BS, a cubic BS, or a PBS.

[0015] In certain embodiments, each of the first reflector and the second reflector is a plane reflector.

[0016] In some embodiments, the first reflector and the second reflector are equidistant from the BS.

[0017] In some embodiments, the beam shear distance module further comprises a first reflector mount and a second reflector mount. The first reflector is mounted on the first reflector mount. In addition, the first reflector mount is controllably rotatable for adjusting a first deflection angle or a first pitch angle, or both, of the first reflector. The second reflector is mounted on the second reflector mount. The second reflector mount is controllably rotatable for adjusting a second deflection angle or a second pitch angle, or both, of the second reflector.

[0018] In certain embodiments, each of the first mirror mount and the second mirror mount is a quick turn mirror mount.

[0019] A second aspect of the present disclosure is to provide a beam shearing module for receiving a second input light and generating a third output light and a fourth output light from the second input light, wherein the third output light and the fourth output light undergo divergent propagation at a controllable shearing angle.

[0020] The beam shearing module includes any of the embodiments of the beam shearing distance module as disclosed above. The beam shearing module also includes a first lens and a second lens. The first lens is used to receive a second input light, and refract the received second input light to form a first input light to be received by the beam shearing distance module. The second lens is used to receive a first output light and a second output light emitted from the beam shearing distance module, and diverge the received first output light and the second output light to form a third output light and a fourth output light diverging at a shearing angle. In particular, the shearing angle can be controlled by controlling the beam shearing distance between the first output light and the second output light.

[0021] In some embodiments, the first lens and the second lens have the same focal length.

[0022] In certain embodiments, each of the first lens and the second lens is implemented as a single lens or a composite lens.

[0023] A third aspect of the present disclosure is to provide a plurality of DIC microscopes, each DIC microscope being used to image a sample.

[0024] The first DIC microscope includes an illumination module, a front-end PBS, a phase tuning module, an objective lens, an imaging module, and any one of the embodiments of the beam shearing module disclosed herein. The illumination module is configured to provide a collimated light beam. The beam shearing module is arranged to receive the collimated light beam as a second input light via the front-end PBS and the phase tuning module, and forward the third output light beam and the fourth output light beam to the objective lens. The objective lens is arranged to focus the third output light beam and the fourth output light beam on the sample so that the sample is illuminated to form an original image of the sample. The beam shearing module is also arranged to capture the original image through the objective lens to convert the captured original image into a phase contrast image of the sample, and transmit the phase contrast image to the front-end PBS via the phase tuning module. The phase tuning module is arranged to tune the phase of the phase contrast image before the phase contrast image reaches the front-end PBS. The front-end PBS is arranged to forward the collimated light beam to the phase tuning module, and turn the phase contrast image to the imaging module. The imaging module is arranged to sense the phase contrast image.

[0025] In some embodiments, the beam shear distance module in the first DIC microscope further comprises a first mirror mount and a second mirror mount, the first mirror being mounted on the first mirror mount and the second mirror being mounted on the second mirror mount. The first mirror mount is controllably rotatable for adjusting a first deflection angle or a first pitch angle or both of the first mirror. The second mirror mount is controllably rotatable for adjusting a second deflection angle or a second pitch angle or both of the second mirror. Additionally, each of the first mirror mount and the second mirror mount is a quick turn mirror mount.

[0026] The second DIC microscope includes an illumination module, a front-end PBS, a phase tuning module, an objective lens, an imaging module, a first beam shearing module, a second beam shearing module, and a polarization modification unit. Each of the first beam shearing module and the second beam shearing module is implemented as any one of the embodiments of the beam shearing module disclosed herein. In the second DIC microscope, a composite module for receiving a third input light and generating a fifth output light and a sixth output light from the third input light is formed by cascading the first beam shearing module, the polarization modification unit, and the second beam shearing module in series. The third input light is the second input light of the first beam shearing module. The fifth output light and the sixth output light are the third output light and the fourth output light of the second beam shearing module, respectively. The illumination module is configured to provide a collimated light beam. The composite module is arranged to receive a collimated light beam as the third input light via the front-end PBS and the phase tuning module, and forward the fifth output light and the sixth output light to the objective lens. The objective lens is arranged to focus the fifth output light and the sixth output light on the sample so that the sample is illuminated to form an original image of the sample. The composite module is also arranged to capture the original image through the objective lens to convert the captured original image into a phase contrast image of the sample, and provide the phase contrast image to the front-end PBS via the phase tuning module. The phase tuning module is arranged to tune the phase of the phase contrast image before the phase contrast image reaches the front-end PBS. The front-end PBS is arranged to forward the collimated light beam to the phase tuning module and turn the phase contrast image to the imaging module. The imaging module is arranged to sense the phase contrast image. The polarization modification unit in the composite module is used to rotate the shearing direction of the fifth output light and the sixth output light, so that when imaging the sample, the sample does not need to be oriented or inconveniently reoriented according to the specific shearing direction of the fifth output light and the sixth output light.

[0027] In some embodiments, the beam shear distance module in the second DIC microscope further comprises a first mirror mount and a second mirror mount, the first mirror being mounted on the first mirror mount and the second mirror being mounted on the second mirror mount. The first mirror mount is controllably rotatable for adjusting a first deflection angle or a first pitch angle or both of the first mirror. The second mirror mount is controllably rotatable for adjusting a second deflection angle or a second pitch angle or both of the second mirror. Additionally, each of the first mirror mount and the second mirror mount is a quick turn mirror mount.

[0028] The third DIC microscope includes an illumination module, a polarizer, a front end BS, a phase tuning module, an objective lens, a polarization imaging module, and any one of the embodiments of the beam shearing module disclosed herein. The illumination module is configured to provide a collimated light beam. The polarizer is arranged to generate a polarization collimated light beam from the collimated light beam. The beam shearing module is arranged to receive the polarization collimated light beam as a second input light via the front end BS and the phase tuning module, and forward the third output light beam and the fourth output light beam to the objective lens. The objective lens is arranged to focus the third output light beam and the fourth output light beam on the sample so that the sample is illuminated to form an original image of the sample. The beam shearing module is also arranged to capture the original image through the objective lens to convert the captured original image into a phase contrast image of the sample, and transmit the phase contrast image to the front end BS via the phase tuning module. The phase tuning module is arranged to tune the phase of the phase contrast image before the phase contrast image reaches the front end BS. The front end BS is arranged to forward the polarization collimated light beam to the phase tuning module, and turn the phase contrast image to the polarization imaging module. The polarization imaging module includes a polarization image sensor for sensing a phase contrast image.

[0029] In some embodiments, the beam shear distance module in the third DIC microscope further comprises a first mirror mount and a second mirror mount, the first mirror being mounted on the first mirror mount and the second mirror being mounted on the second mirror mount. The first mirror mount is controllably rotatable for adjusting a first deflection angle or a first pitch angle or both of the first mirror. The second mirror mount is controllably rotatable for adjusting a second deflection angle or a second pitch angle or both of the second mirror. Additionally, each of the first mirror mount and the second mirror mount is a quick turn mirror mount.

[0030] As shown by the examples below, other aspects of the disclosure are disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a beam shear distance module for generating a first output ray and a second output ray from a first input ray is depicted according to an exemplary embodiment of the present disclosure, wherein the first output ray and the second output ray are parallel and separated by a beam shear distance, and the beam shear distance is in a standard configuration resulting in zero beam shear distance.

[0032] Figure 2 Depicted is a configuration of a beam shear distance module for producing optical shear along the y-direction such that the beam shear distance is positive.

[0033] Figure 3A Depicted is a top view of a beam shear distance module arranged to produce optical shearing along the z-direction.

[0034] Figure 3B Depicted is a perspective view of a beam shear distance module arranged to produce optical shearing along the z-direction.

[0035] Figure 4A Depicted is a top view of a beam shear distance module arranged to generate optical shearing along both the y-direction and the z-direction.

[0036] Figure 4B Depicted is a perspective view of a beam shear distance module arranged to generate optical shearing along both the y-direction and the z-direction.

[0037] Figure 5 Depicted is a schematic diagram of a beam shearing module developed based on a beam shearing distance module for generating third and fourth output rays from a second input ray, wherein the third and fourth output rays undergo divergent propagation at a shearing angle.

[0038] Figure 6 Depicted is a schematic diagram of a first DIC microscope configured to provide a variable shear distance for a pair of light rays used to image a sample.

[0039] Figure 7 Depicted is a schematic diagram of a second DIC microscope configured to provide a variable shear distance for a pair of light rays used to image a sample without the sample needing to be oriented or inconveniently reoriented according to a particular shear direction provided by the pair of light rays.

[0040] Figure 8 Depicted is a schematic diagram of a third DIC microscope configured to provide polarized light to image a sample.

[0041] Fig. 9A As an experimental demonstration, the first image of a sample observed by the first DIC microscope under horizontally sheared light is depicted.

[0042] Fig. 9B As an experimental demonstration, a second image of the sample observed under the first DIC microscope under vertically sheared light is depicted.

[0043] Those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. DETAILED DESCRIPTION

[0044] The present disclosure relates to an optical device, which is referred to as a beam shear distance module and is formed by a BS and two mirrors, for efficiently splitting spatially coherent or incoherent light rays into a pair of parallel beams while eliminating the need to use any birefringent crystal-based prisms in splitting the light rays. By tuning the steering angles of the two mirrors, the shear distance between the two parallel light rays is controllable or programmable. The beam shear distance module can be developed to form a beam shear module that converts the collimated propagation of the pair of parallel light rays into divergent propagation with a controllable shear angle.

[0045] The disclosed beam shear distance module and beam shear module are suitable for use in a DIC microscope. As a result of the efficient control of the shear angle, the image quality and resolution obtained by such a DIC microscope can be improved, and the phase contrast can be accurately quantified. The present disclosure also provides an embodiment of a DIC microscope for achieving rapid switching of the shear direction. This makes the present disclosure ideal for applications requiring high-speed imaging of surface morphology changes, such as phase changes, film wrinkling, mechanical deformation, crack formation and propagation. Therefore, the present disclosure provides new means for studying surface dynamics, water evaporation processes, soft matter deformation, biomechanics, and solid mechanics.

[0046] A first aspect of the present disclosure is to provide a beam shear distance module for generating a first output light ray and a second output light ray from a first input light ray, wherein the first output light ray and the second output light ray are separated by a controllable beam shear distance. Figure 1 , Figure 2 , Figure 3A , Figure 3B , Figure 4A and Figure 4B The disclosed beam shear distance module is explained exemplarily. In these figures, a coordinate system 80 is used as a reference to indicate the geometrical features of the different elements in the beam shear distance module. The coordinate system 80 is formed by an x-direction 81, a y-direction 82 and a z-direction 83.

[0047] Figure 1 A schematic diagram of an exemplary beam shear distance module 100 for generating a first output ray 183 and a second output ray 184 from a first input ray 180 is depicted, wherein the first output ray 183 and the second output ray 184 are parallel and separated by a beam shear distance denoted as s. For purposes of illustration, Figure 1 The beam shear distance module 100 shown in FIG. 1 is specifically configured to have a standard configuration resulting in s=0. Figure 2 Depicted is a configuration of a beam shearing distance module 100 for producing optical shearing along the y-direction 82 such that s is positive.

[0048] The beam shear distance module 100 includes a BS 110, a first reflector 120 and a second reflector 130. When a first input light 180 is incident into the BS 110, the BS 110 splits the first input light 180 into two beams 181 and 182, one of which is a reflected line and the other is transmitted through the BS 110. Finally, it generates a pair of parallel lines, p + 183 and p - 184, there is a precise shear distance s between the two bundles 183, 184. The shear distance s is determined by Figure 1 The beam shear distance of the standard configuration shown in FIG is determined by the geometry of the module 100. The standard configuration gives a zero shear distance, i.e., s=0. Any deviation from the standard configuration generates a positive shear distance. This precise control of the shear distance allows for optimal tuning of contrast and resolution in DIC microscopy.

[0049] The structural and operational details of the beam shear distance module 100 are described in detail below.

[0050] BS110 is configured to split the first input light 180 into a first split light 181 and a second split light 182. The first split light 181 propagates on a first optical path 191, and the second split light 182 propagates on a second optical path 192. In addition, the first optical path 191 and the second optical path 192 define a reference vertical direction perpendicular to the first optical path 191 and the second optical path 192. Figure 1 , Figure 2 , Figure 3A , Figure 3B , Figure 4A and Figure 4B , the reference vertical direction is the z-direction 83. For convenience, the reference vertical direction is labeled 83. The reference vertical direction 83 defines a yaw axis of each of the first reflector 120 and the second reflector 130. The yaw axis of a single reflector selected from the first reflector 120 and the second reflector 130 is the axis of the single reflector parallel to the reference vertical direction 83. The yaw angle (denoted as α) of a single reflector is the rotation angle around the yaw axis. The pitch axis of a single reflector is the axis perpendicular to its yaw axis. The pitch angle (denoted as φ) of a single reflector is the rotation angle around the pitch axis.

[0051] It should be noted that in Figure 1 as well as Figure 2 , Figure 3A , Figure 3B , Figure 4A and Figure 4B, as an example for illustration, the first optical path 191 and the second optical path 192 are drawn to be mutually orthogonal. Physically, if BS 110 is selected as a PBS, the two optical paths 191, 192 are mutually orthogonal. For other types of BSs, the first split light 181 and the second split light 182 propagate along their respective paths, so that the intersection angle between the two optical paths 191, 192 depends on the type of BS used for BS 110 and may not be 90°.

[0052] See also Figure 1 and Figure 2 . The first reflector 120 is located at the distal end 187 of the first optical path 191. The second reflector 130 is located at the distal end 186 of the second optical path 192. It should be noted that the first optical path 191 and the second optical path 192 have a common proximal end 188, wherein the first input light 180 is split into a first split light 181 and a second split light 182. In addition, the first reflector 120 and the second reflector 130 are oriented to achieve the following two effects. First, the first split light 181 is sequentially reflected by the first reflector 120 and then by the second reflector 130 to form a first reflected light 171, which is directed to the BS110 and propagates along a first direction parallel to the second optical path 192. Second, the second split light 182 is sequentially reflected by the second reflector 130 and then by the first reflector 120 to form a second reflected light 172, which is directed to the BS110 and propagates along a second direction parallel to the first optical path 191. It should be noted that the first direction is the x-direction 81, and the second direction is the y-direction 82. For convenience, the first direction and the second direction are labeled 81 and 82, respectively. Equivalently, the first reflector 120 and the second reflector 130 are oriented so that each of the first split light 181 and the second split light 182 undergoes two-stage reflection, so that: (1) the first split light 181 produces a first reflected light 171 directed to the BS 110 and propagating along the first direction 81; and (2) the second split light 182 produces a second reflected light 172 directed to the BS 110 and propagating along the second direction 82. The BS 110 is then reused to process the first reflected light 171 and the second reflected light 172 to produce a first output light 183 and a second output light 184, respectively. It should be noted that the first output light 183 and the second output light 184 propagate along the first direction 81.

[0053] See also Figure 1In the standard configuration, the first output light 183 and the second output light 184 are combined to form a single light beam such that s=0. In the standard configuration, the central axis 121 of the first reflector 120 forms a first angle of 22.5° with the first optical path 191, wherein the central axis 131 of the second reflector 130 forms a second angle of 22.5° with the second optical path 192. It should be noted that Figure 1 The beam shear distance module 100 shown in FIG. 1 is a special case where the first reflector 120 and the second reflector 130 are equidistant from the BS 110. The spacing between the BS 110 and each of the first reflector 120 and the second reflector 130 is d. Although this special case provides a convenient and simple configuration in the actual implementation of the beam shear distance module 100, the present disclosure is not limited to this special case when implementing the disclosed beam shear distance module. It will be understood by those skilled in the art that in the more general case where the first reflector 120 and the second reflector 130 of the beam shear distance module 100 are not equidistant from the BS 110, the corresponding first angle and second angle for achieving s=0 can be easily derived or estimated.

[0054] like Figure 2 The configuration of the beam shear distance module 100 shown in FIG. 1 is capable of generating optical shear. It can be seen that in the special case where the first reflector 120 and the second reflector 130 are equidistant from the BS 110, the shear distance generated along the y-direction 82 is expressed as s y , calculated as follows

[0055] s y =|2d sin(2α)|

[0056] Wherein α is a deflection angle of each of the first mirror 120 and the second mirror 130 relative to a horizontal direction (eg, a direction along the x-direction 81 or the z-direction 83 ).

[0057] Figure 3A and Figure 3B A top view and a perspective view of a beam shear distance module 100 arranged to generate optical shearing along the z-direction 83 are depicted, respectively. It can be seen that in the above special case, the shear distance along the z-direction 83 is given by s z It means that the calculation is as follows

[0058] s z =|2d sin(2φ)|

[0059] Where φ is the pitch angle of each of the first reflector 120 and the second reflector 130 .

[0060] Figure 4A and Figure 4BDepicted are top and perspective views, respectively, of a beam shear distance module 100 arranged to generate optical shearing along both the y-direction 82 and the z-direction 83 by simultaneously varying the deflection angle α and the pitch angle φ of each of the first mirror 120 and the second mirror 130 .

[0061] exist Figure 3A and Figure 3B In FIG. 1 , it is shown that a non-zero shear distance s is obtained by adjusting the two pitch angles of the first reflector 120 and the second reflector 130 jointly (or jointly) at the same angle. Similarly, in Figure 4A and Figure 4B In the embodiment, the non-zero shear distance is obtained by adjusting the two pitch angles of the first reflector 120 and the second reflector 130 together at the same first angle, and also adjusting the two deflection angles thereof together at the same second angle. Figure 3A , Figure 3B , Figure 4A and Figure 4B The beam shear distance module 100 shown in FIG. 1 has a first reflector 120 and a second reflector 130 that are equidistant from the BS 110. Those skilled in the art will appreciate that in the more general case where the first reflector 120 and the second reflector 130 of the beam shear distance module 100 are not equidistant from the BS 110, the corresponding pitch angle and yaw angle of the first reflector 120 and the second reflector 130 that cooperate to achieve a given non-zero shear distance can be easily derived or estimated.

[0062] To summarize, the foregoing analysis indicates that, in the beam shear distance module 100, the deflection angle, the pitch angle, or the orientation of both of the first reflector 120 and the second reflector 130 relative to the reference vertical direction 83 are jointly adjustable to control the beam shear distance s between the first output light 183 and the second output light 184. Therefore, it achieves the following advantages: the beam shear distance s is achievable, controllable, and tunable without using any birefringent crystal-based prisms, such as conventional Wollaston prisms and Nomarski prisms, in the beam shear distance module 100.

[0063] In some embodiments, BS 110 is implemented by a flat BS, a cubic BS, or a PBS.

[0064] In general, it is desirable to keep only a portion of the mirror surface on each of the first reflector 120 and the second reflector 130 flat, wherein the portion of the mirror surface covers a sufficiently large area for reflecting the first partial light ray 181 and the second partial light ray 182 in all configurations. In some embodiments, each of the first reflector 120 and the second reflector 130 is a plane reflector such that the entire mirror surface is flat.

[0065] In some embodiments, the beam shear distance module 100 further includes a first reflector mount 123 and a second reflector mount 133, wherein the first reflector 120 is mounted on the first reflector mount 123, and the second reflector 130 is mounted on the second reflector mount 133. In particular, the first reflector mount 123 is controllably rotatable for adjusting a first deflection angle, a first pitch angle, or both of the first reflector 120. Similarly, the second reflector mount 133 is controllably rotatable for adjusting a second deflection angle, a second pitch angle, or both of the second reflector 130. Those skilled in the art will be able to determine how to control or jointly control the first reflector mount 123 and the second reflector mount 133 according to actual conditions to achieve the desired deflection angle and pitch angle of the first reflector 120 and the second reflector 130. For example, a programmable electronic microcontroller can be used to jointly control the two reflector mounts 123, 133.

[0066] In some embodiments, each of the first reflector mount 123 and the second reflector mount 133 is a fast steering reflector mount. The fast steering reflector mount can be implemented as an electronic reflector mount. Since each of the first reflector 120 and the second reflector 130 driven by the fast steering reflector mount has a faster response time than the liquid crystal, it allows switching between shear directions at a frequency greater than 1000 Hz. The beam shear distance module 100 is capable of shearing in both the y-direction 82 and the z-direction 83 by changing the deflection angle and pitch angle of a single reflector. This design allows accurate and fast switching between the two states.

[0067] A second aspect of the present disclosure is to provide a beam shearing module for generating third and fourth output rays from a second input ray, wherein the third and fourth output rays undergo divergent propagation at a controllable shearing angle. The disclosed beam shearing module is developed based on the beam shearing distance module 100 .

[0068] Figure 5 Depicted is a schematic diagram of an exemplary beam shearing module 500 for receiving a second input ray 580 and generating third and fourth output rays 583 and 584 from the second input ray 580. In particular, the third and fourth output rays 583 and 584 undergo divergent propagation at a controllable shearing angle ε.

[0069] The beam shearing module 500 includes a beam shearing distance module 100, a first lens 510, and a second lens 520. The beam shearing distance module 100 is regarded as any one of the embodiments of the beam shearing distance module 100 disclosed above. The first lens 510 is used to receive the second input light 580, and refract the received second input light 580 to form the first input light 180 to be received by the beam shearing distance module 100. The second lens 520 is used to receive the first output light 183 and the second output light 184 emitted from the beam shearing distance module 100, and diverge the received first output light 183 and the second output light 184 to form the third output light 583 and the fourth output light 584, respectively. In particular, the third output light 583 and the fourth output light 584 diverge at a shearing angle ∈. Advantageously, the shearing angle can be controlled by controlling the beam shearing distance s between the first output light 183 and the second output light 184. It should be noted that with the first lens 510 and the second lens 520, the two spatially sheared light rays 183, 184 are converted from collimated propagation to divergent propagation at a shear angle ∈. The relative shear angle depends entirely on the shear distance s generated by the beam shear distance module 100 and the focal length of the second lens 520. Then, ∈ is given by

[0070]

[0071] Wherein f is the focal length of the second lens 520 .

[0072] Other implementation details of the beam shearing module 500 are provided as follows. In some embodiments, the first lens 510 and the second lens 520 have the same focal length. The first lens 510 and the second lens 520 may also have different focal lengths. Each of the first lens 510 and the second lens 520 may be implemented as a single lens or a composite lens.

[0073] In practice, beam shearing module 500 may be used in a variety of imaging systems including DIC microscopes.

[0074] A third aspect of the present disclosure is to provide a plurality of DIC microscopes developed by utilizing the beam shearing module 500 as disclosed above.

[0075] Figure 6 A schematic diagram of a first DIC microscope 600 for imaging a sample 690 is depicted, wherein the first DIC microscope 600 is configured to provide a variable shear distance for a pair of light rays used to image the sample 690. Advantageously, the configuration of the first DIC microscope 600 provides a high quality phase image with improved contrast and resolution. The first DIC microscope 600 may be referred to as a variable shear distance DIC microscope.

[0076] The first DIC microscope 600 includes an illumination module 610, a front-end PBS 630, a phase tuning module 640, an objective lens 660, an imaging module 620, and a beam shearing module 500. The beam shearing module 500 is regarded as any one of the embodiments of the beam shearing module 500 disclosed above. The illumination module 610 is configured to provide a collimated light beam 615. The beam shearing module 500 is arranged to receive the collimated light beam 615 as a second input ray 580 via the front-end PBS 630 and the phase tuning module 640, and forward a third output ray 583 and a fourth output ray 584 to the objective lens 660. The objective lens 660, which is placed after the beam shearing module 500, is arranged to focus the third output ray 583 and the fourth output ray 584 on a sample 690, so that the sample 690 is illuminated to form a raw image 691 of the sample 690. The objective lens 660 may be any lens having a focal length different from the focal length of the second lens 520 of the beam shearing module 500. The beam shearing module 500 is also arranged to capture a raw image 691 through an objective lens 660, convert the captured raw image 691 into a phase contrast image 625 of the sample 690, and transmit the phase contrast image 625 to the front-end PBS 630 via a phase tuning module 640. The phase tuning module 640 is arranged to tune the phase of the phase contrast image 625 before the phase contrast image 625 reaches the front-end PBS 630. In addition, the optical axis of the phase tuning module 640 is aligned with the optical axis of the beam shearing module 500. The front-end PBS 630 is arranged to forward the collimated light beam 615 to the phase tuning module 640, and to turn the phase contrast image 625 to the imaging module 620. It can be seen that the front-end PBS 630 is used to separate the illumination and imaging paths. In addition, the front-end PBS 630 is oriented at a 45-degree angle relative to the beam shearing module 500. The imaging module 620 is arranged to sense the phase contrast image 625.

[0077] Figure 7 A schematic diagram of a second DIC microscope 700 for imaging a sample 790 is depicted, wherein the second DIC microscope 700 is configured to provide a variable shear distance for a pair of rays for imaging the sample 790 without the sample 790 needing to be oriented or inconveniently reoriented by a particular shear direction provided by the pair of rays. Advantageously, the configuration of the second DIC microscope 600 provides high quality phase images with improved contrast and resolution while avoiding the need to inconveniently orient the sample 790 prior to microscopic examination. The second DIC microscope 700 may be referred to as an orientation-independent variable shear distance DIC microscope.

[0078] The second DIC microscope 700 includes an illumination module 710, a front-end PBS 730, a phase tuning module 740, an objective lens 760, an imaging module 720, a first beam shearing module 500-1, a second beam shearing module 500-2, and a polarization modification unit 755. Each of the first beam shearing module and the second beam shearing module 500-1, 500-2 is implemented as an implementation of the beam shearing module 500. The beam shearing module 500 is regarded as any one of the embodiments of the beam shearing module 500 disclosed above. In the second DIC microscope 700, a compound module 750 is used to receive a third input light ray 751 and generate a fifth output light ray 752 and a sixth output light ray 753 from the third input light ray 751, and the compound module 750 is formed by serially cascading the first beam shearing module 500-1, the polarization modification unit 755, and the second beam shearing module 500-2. In addition, the polarization modification unit 755 has an optical axis positioned at an angle of 45° relative to the optical axis of the first beam shearing module 500-1. The illumination module 710 is configured to provide a collimated light beam 715. The compound module 750 is arranged to receive the collimated light beam 715 as the third input light 751 via the front-end PBS 730 and the phase tuning module 740, and forward the fifth output light 752 and the sixth output light 753 to the objective lens 760. The objective lens 760 is arranged to focus the fifth output light 752 and the sixth output light 753 on the sample 790 so that the sample 790 is illuminated to form an original image 791 of the sample 790. The compound module 750 is also arranged to capture a raw image 791 through the objective lens 760, convert the captured raw image 791 into a phase contrast image 725 of the sample 790, and provide the phase contrast image 725 to the front-end PBS 730 via the phase tuning module 740. The phase tuning module 740 is arranged to tune the phase of the phase contrast image 725 before the phase contrast image 725 reaches the front-end PBS 730. The front-end PBS 730 is arranged to forward the collimated light beam 715 to the phase tuning module 740, and steer the phase contrast image 725 to the imaging module 720. The imaging module 720 is arranged to sense the phase contrast image 725. Advantageously, the polarization modification unit 755 in the compound module 750 is used to rotate the shearing direction of the fifth output light 752 and the sixth output light 753, so that when imaging the sample 790, the sample 790 does not need to be oriented or inconveniently reoriented according to the specific shearing direction of the fifth output light 752 and the sixth output light 753.

[0079] Figure 8A schematic diagram of a third DIC microscope 800 for imaging a sample 890 is depicted, wherein the third DIC microscope 800 is configured to provide polarized light to image the sample 890. Since polarized light is used to image the sample 890, one main application of the third DIC microscope 800 is to detect the phase field of the sample 890. In addition, all liquid crystal elements are removed from the third DIC microscope 800. A polarization camera similar to the third DIC microscope 800 can be used to detect the phase field. The third DIC microscope 800 is capable of determining the state of polarization of the DIC image. The state of polarization is related to the gradient of the surface topography. Therefore, the third DIC microscope 800 can directly detect the phase field without using liquid crystal. The third DIC microscope 800 can be referred to as a single-lens fast-switching double-shear DIC microscope.

[0080] The third DIC microscope 800 includes an illumination module 810, a polarizer 870, a front end BS 830, a phase tuning module 840, an objective lens 860, a polarization imaging module 820, and a beam shearing module 500. The beam shearing module 500 is regarded as any one of the embodiments of the beam shearing module 500 disclosed above. The illumination module 810 is configured to provide a collimated light beam 815. The polarizer 870 is arranged to generate a polarization collimated light beam 816 from the collimated light beam 815. The beam shearing module 500 is arranged to receive the polarization collimated light beam 816 as a second input ray 580 via the front end BS 830 and the phase tuning module 840, and forward the third output ray 583 and the fourth output ray 584 to the objective lens 860. The objective lens 860 is arranged to focus the third output ray 583 and the fourth output ray 584 on the sample 890 so that the sample 890 is illuminated to form an original image 891 of the sample 890. The beam shearing module 500 is also arranged to capture a raw image 891 through the objective lens 860, convert the captured raw image 891 into a phase contrast image 825 of the sample 890, and transmit the phase contrast image 825 to the front-end BS 830 via the phase tuning module 840. The phase tuning module 840 is arranged to tune the phase of the phase contrast image 825 before the phase contrast image 825 reaches the front-end BS 830. The front-end BS 830 is arranged to forward the polarization collimated beam 816 to the phase tuning module 840, and steer the phase contrast image 825 to the polarization imaging module 820. The polarization imaging module 820 includes a polarization image sensor for sensing the phase contrast image 825.

[0081] Advantageously, the beam clipping module 500 for any of the first DIC microscope 600, the second DIC microscope 700 and the third DIC microscope 800 can be mounted together with the first mirror mount 123 and the second mirror mount 133 as fast steering mirror mounts. It allows the DIC microscope under consideration to achieve high-speed inspection of samples.

[0082] By measuring the step-like structure using the first DIC microscope 600 as disclosed above, an experimental demonstration of the disclosed DIC microscope is provided as follows. + 183 and light p - When 184 is irradiated on the step-like structure and reflected back, the phase leg between the two rays is twice the step height. In most existing DIC microscopes, the adopted shear distance is respectively lower than the resolution of these microscopes. It leads to some distortion of the intensity profile being examined. Therefore, the measured phase shift is smaller than the actual step height. Fig. 9A and Fig. 9B As shown in , by increasing the shear distance, the first DIC microscope 600 can clearly and accurately measure the step. Fig. 9A Depicted is the first image of the sample observed under horizontally sheared light. Fig. 9B is the second image of the sample observed under vertically sheared light.

[0083] Without departing from the spirit or essential features of the present disclosure, the present disclosure may be implemented in other specific forms. Therefore, the present embodiment is considered to be illustrative and not restrictive in all aspects. The scope of the present invention is indicated by the appended claims rather than by the preceding description, and therefore, all changes within the meaning and equivalent range of the claims are intended to be included therein.

Claims

1. A beam shear distance module for generating a first output light and a second output light from a first input light, wherein the first output light and the second output light are separated by a controllable beam shear distance, the beam shear distance module comprising: a beam splitter (BS) configured to split the first input light into a first split light and a second split light propagating in a first light path and a second light path, respectively, the first light path and the second light path defining a reference vertical direction perpendicular to the first light path and the second light path; as well as A first reflector and a second reflector are respectively located at the distal ends of the first optical path and the second optical path, and the first reflector and the second reflector are oriented to make each of the first split beam light and the second split beam light undergo two-stage reflection, so that the first split beam light generates a first reflected light ray pointing to the beam splitter and propagating along a first direction parallel to the second optical path, and the second split beam light generates a second reflected light ray pointing to the beam splitter and propagating along a second direction parallel to the first optical path, and the first reflected light ray and the second reflected light ray are processed by the beam splitter to generate the first output light ray and the second output light ray propagating along the first direction, wherein the deflection angle, pitch angle or both orientations of the first reflector and the second reflector relative to the reference vertical direction can be adjusted jointly to control the beam shear distance between the first output light ray and the second output light ray so that the beam shear distance is achievable, controllable and tunable without the need to use any birefringent crystal-based prisms in the beam shear distance module. 2 . The beam shear distance module according to claim 1 , wherein the beam splitter is implemented by a flat plate BS, a cubic BS or a PBS. 3 . The beam shear distance module of claim 1 , wherein each of the first mirror and the second mirror is a plane mirror.

4. The beam shear distance module of claim 1, wherein the first mirror and the second mirror are equidistant from the beam splitter.

5. The beam shear distance module of claim 1 , further comprising: a first reflector mount, the first reflector being mounted on the first reflector mount, the first reflector mount being controllably rotatable for adjusting a first yaw angle or a first pitch angle or both of the first reflector; as well as A second reflector mount, the first reflector is mounted on the second reflector mount, and the second reflector mount is controllably rotatable for adjusting a second deflection angle or a second pitch angle or both of the second reflector.

6. The beam shear distance module of claim 5, wherein each of the first mirror mount and the second mirror mount is a fast steering mirror mount.

7. A beam shearing module for receiving a second input light ray and generating a third output light ray and a fourth output light ray from the second input light ray, the third output light ray and the fourth output light ray undergoing divergent propagation at a controllable shearing angle, the beam shearing module comprising: The beam shear distance module according to claim 1; a first lens for receiving the second input light and refracting the received second input light to form the first input light to be received by the beam shear distance module; as well as a second lens for receiving the first output light and the second output light emitted from the beam shearing distance module and diverging the received first output light and the second output light to form the third output light and the fourth output light diverging at the shearing angle, wherein the shearing angle can be controlled by controlling the beam shearing distance between the first output light and the second output light. The beam shearing module of claim 7 , wherein the first lens and the second lens have the same focal length. 9 . The beam shearing module of claim 7 , wherein each of the first lens and the second lens is implemented as a single lens or a composite lens.

10. A differential interference contrast (DIC) microscope for imaging a sample, the DIC differential interference contrast comprising an illumination module, a front polarization beam splitter (PBS), a phase tuning module, an objective lens, an imaging module and the beam shearing module according to claim 7, wherein: The illumination module is configured to provide a collimated light beam; The beam shearing module is arranged to receive the collimated light beam as the second input light via the front end PBS and the phase tuning module, and forward the third output light and the fourth output light to the objective lens; The objective lens is arranged to focus the third output light and the fourth output light on the sample so that the sample is illuminated to form an original image of the sample; The beam shearing module is further arranged to capture the raw image through the objective lens, convert the captured raw image into a phase contrast image of the sample, and transmit the phase contrast image to the front end PBS via the phase tuning module; The phase tuning module is arranged to tune the phase of the phase contrast image before the phase contrast image reaches the front end PBS; The front end PBS is arranged to forward the collimated beam to the phase tuning module and steer the phase contrast image to the imaging module; and The imaging module is arranged to sense the phase contrast image.

11. The differential interference contrast microscope of claim 10, wherein the beam shear distance module further comprises: a first reflector mount, the first reflector being mounted on the first reflector mount, the first reflector mount being controllably rotatable for adjusting a first yaw angle or a first pitch angle or both of the first reflector; as well as a second reflector mount on which the first reflector is mounted, the second reflector mount being controllably rotatable for adjusting a second yaw angle or a second pitch angle or both of the second reflector; Wherein each of the first reflector mount and the second reflector mount is a quick turn reflector mount.

12. A differential interference contrast (DIC) microscope for imaging a sample, the differential interference contrast microscope comprising an illumination module, a front polarization beam splitter (PBS), a phase tuning module, an objective lens, an imaging module, a first beam shearing module, a second beam shearing module and a polarization modification unit, wherein: Each of the first beam cutting module and the second beam cutting module is implemented as the beam cutting module according to claim 7; a composite module for receiving a third input light and generating a fifth output light and a sixth output light from the third input light, the composite module being formed by serially cascading the first beam shearing module, the polarization modifying unit, and the second beam shearing module, wherein the third input light is the second input light of the first beam shearing module, and wherein the fifth output light and the sixth output light are the third output light and the fourth output light of the second beam shearing module, respectively; The illumination module is configured to provide a collimated light beam; The compound module is arranged to receive the collimated light beam as the third input light via the front-end PBS and the phase tuning module, and forward the fifth output light and the sixth output light to the objective lens; The objective lens is arranged to focus the fifth output light and the sixth output light on the sample so that the sample is illuminated to form an original image of the sample; The composite module is further arranged to capture the raw image through the objective lens to convert the captured raw image into a phase contrast image of the sample, and provide the phase contrast image to the front-end PBS via the phase tuning module; The phase tuning module is arranged to tune the phase of the phase contrast image before the phase contrast image reaches the front end PBS; The front end PBS is arranged to forward the collimated beam to the phase tuning module and steer the phase contrast image to the imaging module; The imaging module is arranged to sense the phase contrast image; and The polarization modification unit in the composite module is used to rotate the shearing direction of the fifth output light and the sixth output light, so that when imaging the sample, the sample does not need to be oriented or inconveniently reoriented according to the specific shearing direction of the fifth output light and the sixth output light.

13. The differential interference contrast microscope of claim 12, wherein each of the first beam shearing module and the second beam shearing module further comprises: a first reflector mount, the first reflector being mounted on the first reflector mount, the first reflector mount being controllably rotatable for adjusting a first yaw angle or a first pitch angle or both of the first reflector; as well as a second reflector mount on which the first reflector is mounted, the second reflector mount being controllably rotatable for adjusting a second yaw angle or a second pitch angle or both of the second reflector; Wherein each of the first reflector mount and the second reflector mount is a quick turn reflector mount.

14. A differential interference contrast (DIC) microscope for imaging a sample, the differential interference contrast microscope comprising an illumination module, a polarizer, a front beam splitter (BS), a phase tuning module, an objective lens, a polarization imaging module and the beam shearing module according to claim 7, wherein: The illumination module is configured to provide a collimated light beam; The polarizer is arranged to generate a polarized collimated light beam from the collimated light beam; The beam shearing module is arranged to receive the polarization collimated light beam as the second input light via the front end BS and the phase tuning module, and forward the third output light and the fourth output light to the objective lens; The objective lens is arranged to focus the third output light and the fourth output light on the sample so that the sample is illuminated to form an original image of the sample; The beam shearing module is further arranged to capture the raw image through the objective lens to convert the captured raw image into a phase contrast image of the sample, and transmit the phase contrast image to the front end BS via the phase tuning module; The phase tuning module is arranged to tune the phase of the phase contrast image before the phase contrast image reaches the front end BS; The front end BS is arranged to forward the polarization collimated light beam to the phase tuning module and steer the phase contrast image to the polarization imaging module; and The polarization imaging module includes a polarization image sensor for sensing the phase contrast image.

15. The differential interference contrast microscope of claim 14, wherein the beam shear distance module further comprises: a first reflector mount, the first reflector being mounted on the first reflector mount, the first reflector mount being controllably rotatable for adjusting a first yaw angle or a first pitch angle or both of the first reflector; as well as a second reflector mount on which the first reflector is mounted, the second reflector mount being controllably rotatable for adjusting a second yaw angle or a second pitch angle or both of the second reflector; Wherein each of the first reflector mount and the second reflector mount is a quick turn reflector mount.

Images