A large field-of-view four-directional shear speckle interferometry apparatus and method for polarization multiplexing
By designing a polarization-multiplexed Mach-Zehnder interferometer structure and a 4f optical system, the problem that the DSSPI system cannot achieve large field of view and multi-directional defect detection was solved, and efficient and sensitive detection of four-directional shear speckle interferometry was realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG SCI-TECH UNIV
- Filing Date
- 2022-09-30
- Publication Date
- 2026-06-30
AI Technical Summary
The existing DSSPI system cannot achieve multi-directional defect detection and large field-of-view measurement of large-sized test samples, and cannot simultaneously measure deformation information in four shear directions.
A polarization-multiplexed Mach-Zehnder interferometer structure was designed and combined with a 4f optical system to achieve four-direction shear speckle interferometry. The shear direction and carrier frequency were adjusted by a polarizing beam splitter and an aperture stop, and the interferograms of the four object beams were acquired by a CCD.
It achieves large field-of-view measurement, enabling simultaneous measurement of deformation information in four shear directions, thus improving measurement efficiency and sensitivity, and is suitable for performance and defect evaluation of composite materials.
Smart Images
Figure CN116026245B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of shear speckle interferometry technology, specifically relating to a large field-of-view four-directional shear speckle interferometry device and method with polarization multiplexing. Background Technology
[0002] Digital shear speckle interferometry (DSSPI) can directly measure the derivative of an object's deformation and features full-field non-contact, high precision, and high sensitivity. It is widely used in steady-state vibration analysis of objects, deflection angle measurement, and performance and defect evaluation of composite materials.
[0003] When the DSSPI system is used for defect assessment, it measures the first derivative of the deformation of the test object along the shear direction, and the sensitivity of defect detection is determined by the shear direction. However, the defect direction of a product during the manufacturing process is not unique. Using a single-direction DSSPI system requires detection in at least two perpendicular directions to assess the multi-directional defect distribution of the sample; otherwise, defects parallel to the shear direction will be missed. Therefore, simultaneous detection of multi-directional shear in a single operation has become a research focus of DSSPI. Furthermore, in the aerospace field, large-sized test specimens place high demands on the measurement range, making large field-of-view measurement a requirement for DSSPI applications. However, existing DSSPI systems can only achieve simultaneous measurement in two or three shear directions and have not solved the problem of the measurement field of view being limited by the size of the beam splitter prism, thus failing to meet the measurement needs of large-sized test specimens. Summary of the Invention
[0004] To address the shortcomings of existing methods, the present invention aims to provide a large field-of-view four-directional shear speckle interferometry measurement device and method with polarization multiplexing. A 4f optical system is embedded in the optical path to achieve large field-of-view measurement; a polarization multiplexing Mach-Zehnder interferometer structure is designed to achieve simultaneous measurement of deformation information in four shear directions, thereby improving the efficiency of shear speckle interferometry measurement.
[0005] The specific technical solution adopted by the present invention to achieve the above objectives is as follows:
[0006] I. A large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing:
[0007] The device includes a laser, a quarter-wave plate, a first reflecting mirror, a beam expander, an imaging lens, a first lens, a first beam splitter, a first polarizing beam splitter, a second beam splitter, a second reflecting mirror, a third reflecting mirror, a fourth reflecting mirror, a fifth reflecting mirror, a first aperture stop, a second aperture stop, a third aperture stop, a fourth aperture stop, a second lens, a third lens, a fourth lens, a fifth lens, a third beam splitter, a second polarizing beam splitter, a fourth beam splitter, and a CCD;
[0008] The light emitted by the laser passes sequentially through a quarter-wave plate, a first reflecting mirror, and a beam expander before illuminating the surface of the object under test. After diffuse reflection from the surface of the object, the light passes through an imaging lens and is imaged on the focal plane of the imaging lens. Then, after being transmitted through the first lens, it is incident on the first beam splitter, where it undergoes reflection and transmission to split into two beams: a transmitted beam and a reflected beam.
[0009] The transmitted beam from the first beam splitter serves as the first object beam, which is reflected sequentially by the second reflecting mirror, the first aperture stop, the second lens, and the fourth beam splitter before illuminating the target surface of the CCD. The reflected beam from the first beam splitter is then incident on the first polarizing beam splitter, where it is reflected and transmitted to split into two beams: vertically polarized light and horizontally polarized light. The vertically polarized light serves as the second object beam, which is reflected sequentially by the third reflecting mirror, the second aperture stop, the third lens, the second polarizing beam splitter, and the fourth beam splitter before illuminating the target surface of the CCD.
[0010] Horizontally polarized light is incident on the second beam splitter and is reflected and transmitted to be split into two beams. The light reflected by the second beam splitter becomes the third object beam, which passes through the fourth reflecting mirror, the third aperture stop, the fourth lens, the third beam splitter, the second polarizing beam splitter, and the fourth beam splitter in sequence before illuminating the target surface of the CCD. The light transmitted by the second beam splitter becomes the fourth object beam, which passes through the fifth reflecting mirror, the fourth aperture stop, the fifth lens, the third beam splitter, the second polarizing beam splitter, and the fourth beam splitter in sequence before illuminating the target surface of the CCD.
[0011] The first, second, third, fourth, and fifth lenses have the same focal length, which is f. The image plane of the imaging lens is located at the front focal plane of the first lens. The optical path between the first lens and the second, third, fourth, and fifth lenses is 2f. The target surface of the CCD is located at the rear focal plane of the second, third, fourth, and fifth lenses, which coincides with the first lens, thus forming four 4f optical systems.
[0012] Rotate and adjust the second, third, fourth, and fifth reflectors to adjust the shear direction and shear amount between the four object beams.
[0013] The shearing refers to the mutual misalignment when the object light is irradiated onto the CCD target surface.
[0014] The shearing direction refers to the direction of mutual misalignment when two beams of object light are irradiated onto the CCD target surface.
[0015] The shearing amount refers to the misalignment offset of two beams of object light when they are irradiated onto the CCD target surface.
[0016] Adjust the relative positions of the first aperture stop 15, the second aperture stop 16, the third aperture stop 17 and the fourth aperture stop 18 to adjust the spatial carrier frequency of their respective object light.
[0017] In practice, a load is applied to the object under test to cause slight deformation, and the CCD26 collects the interferograms of the object before and after the deformation.
[0018] The linearly polarized beam emitted by the laser of the present invention becomes a circularly polarized beam after passing through a quarter-wave plate. After passing through a reflector and a beam expander in sequence to illuminate the object under test, diffuse reflection occurs. Then, after passing through an imaging lens and a lens, it is split into four object beams containing different polarization states by two beam splitters and a polarizing beam splitter. The four object beams are then illuminated onto the CCD target surface after passing through a reflector, a lens, an aperture stop, and a beam splitter, respectively.
[0019] II. A large field-of-view four-directional shear speckle interferometry method based on polarization multiplexing:
[0020] 1) The laser beam emitted by the laser passes through a quarter-wave plate, a first reflecting mirror and a beam expander in sequence and then illuminates the object under test, causing diffuse reflection. The diffusely reflected light is split into four beams of object light containing three polarization states by a beam splitter and a polarizing beam splitter.
[0021] 2) Apply a load to the object under test to cause slight deformation. Use a CCD to collect interferograms before and after the deformation of the object under test. In this way, the CCD collects large field-of-view four-directional shear speckle interferograms of the object under test before and after the deformation based on polarization multiplexing.
[0022] 3) Perform Fourier transform on the acquired four-directional shear speckle interferogram to obtain the spectrum of the four-directional shear speckle interferogram;
[0023] 4) Extract the spectral components corresponding to the shearing direction x, shearing direction y, 45-degree shearing direction and 135-degree shearing direction from the spectral diagram of the four-direction shear speckle interferogram, respectively, and perform inverse Fourier transform to obtain the phase diagram containing the shearing direction x, shearing direction y, 45-degree shearing direction and 135-degree shearing direction, respectively.
[0024] 5) Subtract the phase diagrams containing shear direction x, shear direction y, 45-degree shear direction and 135-degree shear direction before and after deformation of the object to be measured, respectively, to obtain deformation phase diagrams containing deformation information of shear direction x, shear direction y, 45-degree shear direction and 135-degree shear direction.
[0025] 6) Extract the deformation of the object under test from the deformation phase diagram.
[0026] In step 1), by rotating and adjusting the second, third, fourth, and fifth reflectors, the shearing direction and shearing amount between the four object beams are adjusted so that the shearing direction between the first and second object beams is a 135-degree oblique shearing direction, the shearing direction between the first and third object beams is shearing direction x, the shearing direction between the first and fourth object beams is shearing direction y, and the shearing direction between the third and fourth object beams is a 45-degree oblique shearing direction.
[0027] The shearing direction x is parallel to the target surface of the CCD and along the horizontal direction, the shearing direction y is parallel to the target surface of the CCD and along the vertical direction, the oblique 135-degree shearing direction is specifically the shearing direction x on the target surface of the CCD rotated 45 degrees clockwise, and the oblique 45-degree shearing direction is specifically the shearing direction x on the target surface of the CCD rotated 45 degrees counterclockwise.
[0028] In step 2), the spatial carrier frequency of the object light is adjusted by adjusting the relative positions of the four aperture stops in the shearing direction x and shearing direction y.
[0029] The beneficial effects of this invention are:
[0030] (1) The present invention transmits images by embedding a 4f optical system in the optical path. Only the focal length of the imaging lens or the size of the CCD pixel needs to be changed to achieve a large field of view measurement and a large measurement range.
[0031] (2) The present invention uses a Mach-Zehnder interferometer structure to form four object beams. Combined with polarization design to prevent unwanted cross interference, it can achieve simultaneous measurement in four shear directions with high measurement efficiency.
[0032] In summary, this invention embeds a 4f optical system in the optical path to expand the viewing angle and achieve large field-of-view measurement; it designs a polarization-multiplexed Mach-Zehnder interferometer structure to simultaneously measure deformation information in four shear directions, which has the advantages of large measurement range, high detection efficiency and high sensitivity, and can be widely used in the field of shear speckle interferometry measurement technology for performance and defect evaluation of composite materials. Attached Figure Description
[0033] Figure 1 This is a schematic diagram of the device of the present invention.
[0034] Figure 2 This is a schematic diagram of the translation between the four object beams.
[0035] Figure 3 This is a schematic diagram showing the distribution of the nine spectral components in the frequency domain.
[0036] In the diagram: 1. Laser, 2. Quarter-wave plate, 3. First reflecting mirror, 4. Beam expander, 5. Object under test, 6. Imaging lens, 7. First lens, 8. First beam splitter, 9. First polarizing beam splitter, 10. Second beam splitter, 11. Second reflecting mirror, 12. Third reflecting mirror, 13. Fourth reflecting mirror, 14. Fifth reflecting mirror, 15. First aperture stop, 16. Second aperture stop, 17. Third aperture stop, 18. Fourth aperture stop, 19. Second lens, 20. Third lens, 21. Fourth lens, 22. Fifth lens, 23. Third beam splitter, 24. Second polarizing beam splitter, 25. Fourth beam splitter, 26. CCD. Detailed Implementation
[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0038] like Figure 1 As shown, the present invention includes a laser 1, a quarter-wave plate 2, a first reflecting mirror 3, a beam expander 4, an imaging lens 6, a first lens 7, a first beam splitter 8, a first polarizing beam splitter 9, a second beam splitter 10, a second reflecting mirror 11, a third reflecting mirror 12, a fourth reflecting mirror 13, a fifth reflecting mirror 14, a first aperture stop 15, a second aperture stop 16, a third aperture stop 17, a fourth aperture stop 18, a second lens 19, a third lens 20, a fourth lens 21, a fifth lens 22, a third beam splitter 23, a second polarizing beam splitter 24, a fourth beam splitter 25, and a CCD 26.
[0039] The laser emitted by laser 1 is reflected sequentially by quarter-wave plate 2, first reflecting mirror 3, and beam expander 4 before illuminating the surface of object 5 under test. The light after diffuse reflection from the surface of object 5 under test contains various polarization states. After diffuse reflection from the surface of object 5 under test test, the light is imaged on the focal plane of imaging lens 6, and then transmitted through first lens 7 before being incident on first beam splitter 8, where it is reflected and transmitted to be split into two beams: a transmitted beam and a reflected beam.
[0040] The transmitted beam from the first beam splitter 8 serves as the first object beam, which is reflected sequentially by the second reflecting mirror 11, the first aperture stop 15, the second lens 19, and the fourth beam splitter 25 before illuminating the target surface of the CCD 26. The reflected beam from the first beam splitter 8 is then incident on the first polarizing beam splitter 9, where it is reflected and transmitted to split into two beams: vertically polarized light and horizontally polarized light. The vertically polarized light reflected by the first polarizing beam splitter 9 serves as the second object beam, which is reflected sequentially by the third reflecting mirror 12, the second aperture stop 16, the third lens 20, the second polarizing beam splitter 24, and transmitted through the fourth beam splitter 25 before illuminating the target surface of the CCD 26.
[0041] The horizontally polarized light transmitted by the first polarizing beam splitter 9 is then incident on the second beam splitter 10, where it is reflected and transmitted to form two beams. The light reflected by the second beam splitter 10 serves as the third object beam, which passes sequentially through the fourth reflecting mirror 13, the third aperture stop 17, the fourth lens 21, the third beam splitter 23 (reflection), the second polarizing beam splitter 24 (transmission), and the fourth beam splitter 25 (transmission) before illuminating the target surface of the CCD 26. The light transmitted by the second beam splitter 10 serves as the fourth object beam, which passes sequentially through the fifth reflecting mirror 14, the fourth aperture stop 18, the fifth lens 22, the third beam splitter 23 (transmission), the second polarizing beam splitter 24 (transmission), and the fourth beam splitter 25 (transmission) before illuminating the target surface of the CCD.
[0042] The focal lengths of the first lens 7, the second lens 19, the third lens 20, the fourth lens 21, and the fifth lens 22 are all the same, which is f. The image plane of the imaging lens 6 is located at the front focal plane of the first lens 7. The optical path lengths along the optical axis from the first lens 7 to the second lens 19, the third lens 20, the fourth lens 21, and the fifth lens 22 are all 2f. The rear focal planes of the second lens 19, the third lens 20, the fourth lens 21, and the fifth lens 22 coincide. The target surface of the CCD 26 is located at the rear focal plane of the second lens 19, the third lens 20, the fourth lens 21, and the fifth lens 22, which constitutes four 4f optical systems.
[0043] Specifically, the first lens 7 and the second lens 19 form a 4f optical system; the first lens 7 and the third lens 20 form a 4f optical system; the first lens 7 and the fourth lens 21 form a 4f optical system; and the first lens 7 and the fifth lens 22 form a 4f optical system.
[0044] The second reflector 11, the third reflector 12, the fourth reflector 13, and the fifth reflector 14 are rotated and adjusted about a direction perpendicular to the optical axis to adjust the shearing direction and shearing amount between the four object beams.
[0045] The four object beams illuminating the CCD target surface contain three polarization states: the first object beam has both horizontal and vertical polarization, the second object beam has only vertical polarization, and the third and fourth object beams are both horizontally polarized. Two object beams serve as reference beams to each other and can interfere with each other: the vertically polarized light in the first object beam interferes with the second object beam; the horizontally polarized light in the first object beam interferes with both the third and fourth object beams; and the third and fourth object beams also interfere with each other. The polarization direction of the second object beam is perpendicular to that of the third and fourth object beams, and therefore does not interfere. This results in the interference field on the CCD target surface being a superposition of four interference fields. Therefore, by adjusting the shearing direction and shearing amount among the four object beams, an interference pattern containing all four shearing directions can be acquired simultaneously.
[0046] Shearing refers to the misalignment of objects when they are irradiated onto the CCD target surface.
[0047] The shear direction refers to the direction of mutual misalignment when two beams of object light are irradiated onto the CCD target surface.
[0048] Shearing amount refers to the amount of misalignment between two beams of object light when they are irradiated onto the CCD target surface.
[0049] Adjusting the relative positions of the first aperture stop 15, the second aperture stop 16, the third aperture stop 17, and the fourth aperture stop 18 adjusts the spatial carrier frequency of the corresponding object light, thereby adjusting the acquisition of the interferogram and making the acquisition of the interferogram better.
[0050] The specific implementation process of this invention is as follows:
[0051] The linearly polarized beam emitted by laser 1 becomes a circularly polarized beam after passing through a quarter-wave plate 2. It then passes sequentially through a first reflecting mirror 3 and a beam expander 4 to illuminate the object under test 5, resulting in diffuse reflection. Next, it passes through an imaging lens 6 and a first lens 7, and is split into four beams containing three polarization states by a first beam splitter 8, a first polarizing beam splitter 9, and a second beam splitter 10. Assuming the measurement is under... The four beams of light reaching the CCD surface are respectively... , , and Its expression is described as:
[0052] (1)
[0053] in: , , and These represent the amplitudes of the four beams of light. The phase of the object light wave; and Representing object light waves respectively Compared to Translation of the CCD target surface along the shear direction x and shear direction y Represents object light wave Compared to The amount of translation along the shear direction x on the CCD target surface Represents object light wave Compared to The amount of translation along the shear direction y on the CCD target surface; and Representing object light waves respectively Spatial carrier frequencies in the shearing directions x and y Represents object light wave The spatial carrier frequency in the shear direction x Represents object light wave The spatial carrier frequency in the shear direction y.
[0054] The four object beams serve as reference beams for each other, and the portions of the beams with the same polarization direction can interfere with each other. The second, third, fourth, and fifth reflecting mirrors are rotated and adjusted to regulate the shearing direction and amount between the four object beams. The shearing direction between the first and second object beams is at a 135-degree angle; the shearing direction between the first and third object beams is shearing direction x; the shearing direction between the first and fourth object beams is shearing direction y; and the shearing direction between the third and fourth object beams is at a 45-degree angle. Figure 2 The diagram illustrates the translation between the four object beams, where... and Less than 0, and Greater than 0, and , .
[0055] The relative positions of the four aperture stops are adjusted to regulate the magnitude of the corresponding object light spatial carrier frequency. A total of three carrier frequencies are introduced into the object light wave. , and In the middle, they are:
[0056] (2)
[0057] in, Indicates the wavelength of the light source. Represents object light wave carrier frequency, Indicates. Object light wave carrier frequency, Represents object light wave carrier frequency, and These are the reference angles in the shearing direction x and shearing direction y, respectively, for the second aperture stop 16 to be misaligned relative to the first aperture stop 15. It is the reference angle in the shearing direction x, where the third aperture stop 17 is misaligned relative to the first aperture stop 15. It is the reference angle in the shearing direction y, where the fourth aperture stop 18 is misaligned relative to the first aperture stop 15.
[0058] The CCD simultaneously acquires interferograms containing four shear directions, and their intensity maps are described as follows:
[0059] (3)
[0060] in, This represents the intensity at coordinates (x, y) in the interferogram. , , and These represent the first, second, third, and fourth beams of light, respectively, with "*" representing the conjugate operator.
[0061] Performing a Fourier transform on equation (3) yields the frequency domain expression:
[0062] (4)
[0063] Where I represents the intensity map of the interferogram, This represents the Fourier transform operation. This represents the convolution operation. , Indicates its conjugate term, , Indicates its conjugate term, , Indicates its conjugate term, , It indicates its conjugate term.
[0064] Decompose equation (4) into 9 terms: A, B, B*, C, C*, D, D*, E, E*.
[0065] A represents the zero-level item, which contains background light information:
[0066] (5)
[0067] B and B* represent the positive and negative first-order spectral terms of the interference part between the first and third object beams, respectively, containing phase information in the shearing direction x:
[0068] (6)
[0069] C and C* represent the positive and negative first-order spectral terms of the interference part between the first and fourth object beams, respectively, containing phase information in the shearing direction y:
[0070] (7)
[0071] D and D* represent the positive and negative first-order spectral terms of the interference part of the third and fourth object beams, respectively, including phase information in the 45-degree shear direction:
[0072] (8)
[0073] E and E* represent the positive and negative first-order spectral terms of the interference portion of the first and second object beams, respectively, containing phase information along the 135-degree shear direction:
[0074] (9)
[0075] By introducing a suitable carrier frequency into the optical path, the nine spectral components can be separated in the frequency domain. Figure 3 The diagram illustrates the distribution of the nine spectral components in the frequency domain.
[0076] Spectral components corresponding to the shear direction x, shear direction y, 45° shear direction, and 135° shear direction are extracted from the spectral diagrams of the shear speckle interferograms in the four directions before deformation. Inverse Fourier transforms are then performed to obtain phase diagrams containing the shear directions x, y, 45°, and 135° shear directions. The phase difference in the four shear directions is denoted as:
[0077] (10)
[0078] in, , , , These represent the phase differences along the shear direction x, shear direction y, 45-degree oblique shear direction, and 135-degree oblique shear direction, respectively. This indicates the phase of the first beam of object light before deformation. This indicates the phase of the second beam of light before deformation. This indicates the phase of the third beam of light before deformation. This indicates the phase of the fourth beam of light before deformation. and Representing object light waves respectively Compared to Translation of the CCD target surface along the shear direction x and shear direction y Represents object light wave Compared to The amount of translation along the shear direction x on the CCD target surface Represents object light wave Compared to The amount of translation along the shear direction y on the CCD target surface.
[0079] A load is applied to the object under test 5 to cause a slight deformation, and the CCD26 acquires the interference pattern of the object under test 5 before and after the deformation.
[0080] Similarly, by processing the interference pattern after deformation, we can obtain... , , and Subtract the phase diagrams before and after deformation, assuming the angle between the illumination direction and the observation direction is... The optical phase difference caused by the surface deformation of the object under test 5 is obtained:
[0081] (11)
[0082] , , ,
[0083] , , ,
[0084] in, The deformation of the surface of the object to be tested, 5. This indicates the shearing amount between the first and second object beams. This indicates the shearing amount between the first and third object beams. This indicates the shearing amount between the first and fourth object beams. This indicates the shearing amount between the third and fourth object beams; This indicates the shearing direction between the first and second object beams. This indicates the shear direction between the first and third object beams. This indicates the shearing direction between the first and fourth object beams. Indicates the shear direction between the third and fourth object beams. and Representing object light waves respectively Compared to Translation of the CCD target surface along the shear direction x and shear direction y Represents object light wave Compared to The amount of translation along the shear direction x on the CCD target surface Represents object light wave Compared to The amount of translation along the shear direction y on the CCD target surface; This indicates the angle between the lighting direction and the observation direction.
[0085] Based on the phase difference distribution diagrams corresponding to different shear directions, deformation information in different shear directions can be detected.
[0086] In this embodiment, laser 1 is a single-mode frequency-stabilized laser (MSL-FN-532-300mW) from Changchun New Industries Optoelectronic Technology Co., Ltd., with an output linearly polarized light wavelength of λ=532nm. CCD 26 uses a VLG-20M high-resolution camera from Baumer, Germany, with a resolution of 1624×1228 pixels and a pixel size of 4.4μm×4.4μm. The object under test 5 is an aluminum plate with a diameter of 180mm, fixed on a steel frame. A spiral micro-head is mounted behind the steel frame, and a concentrated central force load is applied to the aluminum plate by rotating the spiral micro-head to induce deformation. The imaging lens 6 has a focal length of 16mm, and the first lens 7, second lens 19, third lens 20, fourth lens 21, and fifth lens 22 all have focal lengths of 200mm. Measurements show that at a working distance of 210mm, the system has horizontal and vertical viewing angles of 25.3° and 18.9° respectively, with a field of view of 94mm×70mm.
[0087] As can be seen from the above embodiments, the present invention embeds a 4f optical system in the optical path, expands the viewing angle, and realizes a large field of view measurement; the rotating mirror adjusts the shear amount, and the relative position of the aperture stop is adjusted to introduce the carrier frequency, so that the adjustment of shear amount and carrier amount are independent of each other; the Mach-Zehnder interferometer structure is multiplexed to form four object beams, and the polarization design is used to avoid unwanted cross interference, which effectively realizes simultaneous measurement in four shear directions, improves measurement efficiency, and has outstanding technical effects.
[0088] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.
Claims
1. A large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing, characterized in that: Includes a laser (1), a quarter-wave plate (2), a first reflecting mirror (3), a beam expander (4), an imaging lens (6), a first lens (7), a first beam splitter (8), a first polarizing beam splitter (9), a second beam splitter (10), a second reflecting mirror (11), a third reflecting mirror (12), a fourth reflecting mirror (13), a fifth reflecting mirror (14), a first aperture stop (15), a second aperture stop (16), a third aperture stop (17), a fourth aperture stop (18), a second lens (19), a third lens (20), a fourth lens (21), a fifth lens (22), a third beam splitter (23), a second polarizing beam splitter (24), a fourth beam splitter (25), and a CCD (26); The light emitted by the laser (1) is reflected by a quarter-wave plate (2), a first reflecting mirror (3), and expanded by a beam expander (4) before illuminating the surface of the object under test (5). After diffuse reflection from the surface of the object under test (5), the light passes through an imaging lens (6) and is imaged on the focal plane of the imaging lens (6). Then, after being transmitted through the first lens (7), the light is incident on the first beam splitter (8) and undergoes reflection and transmission to split into two beams: a transmitted beam and a reflected beam. The transmitted beam from the first beam splitter (8) serves as the first object beam. After being reflected by the second mirror (11), the first aperture stop (15), the second lens (19), and the fourth beam splitter (25), it illuminates the target surface of the CCD (26). The reflected beam from the first beam splitter (8) is then incident on the first polarizing beam splitter (9) and undergoes reflection and transmission to split into two beams: vertically polarized light and horizontally polarized light. The vertically polarized light serves as the second object beam. After being reflected by the third mirror (12), the second aperture stop (16), the third lens (20), the second polarizing beam splitter (24), and the fourth beam splitter (25), it illuminates the target surface of the CCD (26). Horizontally polarized light is incident on the second beam splitter (10) and is reflected and transmitted to be split into two beams. The light reflected by the second beam splitter (10) serves as the third object beam, which passes through the fourth reflecting mirror (13), the third aperture stop (17), the fourth lens (21), the third beam splitter (23), the second polarizing beam splitter (24), and the fourth beam splitter (25) in sequence before illuminating the target surface of the CCD (26). The light transmitted by the second beam splitter (10) serves as the fourth object beam, which passes through the fifth reflecting mirror (14), the fourth aperture stop (18), the fifth lens (22), the third beam splitter (23), the second polarizing beam splitter (24), and the fourth beam splitter (25) in sequence before illuminating the target surface of the CCD. The focal lengths of the first lens (7), the second lens (19), the third lens (20), the fourth lens (21), and the fifth lens (22) are all the same, which is f. The image plane of the imaging lens (6) is located on the front focal plane of the first lens (7). The optical path between the first lens (7) and the second lens (19), the third lens (20), the fourth lens (21), and the fifth lens (22) is 2f. The target surface of the CCD (26) is located on the back focal plane that overlaps with the second lens (19), the third lens (20), the fourth lens (21), and the fifth lens (22), thus forming four 4f optical systems.
2. The large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing according to claim 1, characterized in that: Rotate and adjust the second reflector (11), the third reflector (12), the fourth reflector (13) and the fifth reflector (14) to adjust the shear direction and shear amount between the four object beams.
3. The large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing according to claim 1, characterized in that: Adjust the relative positions of the first aperture stop (15), the second aperture stop (16), the third aperture stop (17) and the fourth aperture stop (18) to adjust the spatial carrier frequency of their respective object light.
4. A measurement method applied to the large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing as described in any one of claims 1-3, characterized in that, The methods specifically include: 1) The light beam emitted by the laser (1) illuminates the object to be tested (5) and undergoes diffuse reflection. The diffusely reflected light is split into four beams of object light containing three polarization states by the beam splitter and polarizing beam splitter. 2) Apply a load to the object to be measured (5) to cause deformation of the object to be measured (5), and use CCD (26) to collect interferograms before and after the deformation of the object to be measured (5); 3) Perform Fourier transform on the acquired four-directional shear speckle interferogram to obtain the spectrum of the four-directional shear speckle interferogram; 4) Extract the corresponding shear direction from the spectrum of the four-directional shear speckle interferograms. x shear direction y The spectral components of the 45-degree and 135-degree shear directions are subjected to inverse Fourier transform to obtain phase diagrams containing shear direction x, shear direction y, 45-degree and 135-degree shear directions, respectively. 5) Determine the shear direction of the object to be tested (5) before and after deformation. x shear direction y Subtract the phase diagrams of the 45-degree and 135-degree shear directions respectively to obtain the phase diagrams containing the shear directions. x shear direction y Deformation phase diagrams showing deformation information in the 45-degree and 135-degree oblique shear directions; 6) Extract the deformation of the object under test (5) from the deformation phase diagram.
5. The measurement method of the large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing according to claim 4, characterized in that: In step 1), the shearing direction and shearing amount between the four object beams are adjusted by rotating and adjusting the second reflector (11), the third reflector (12), the fourth reflector (13), and the fifth reflector (14), so that the shearing direction between the first object beam and the second object beam is a 135-degree oblique shearing direction, and the shearing direction between the first object beam and the third object beam is a shearing direction. x The shearing direction between the first and fourth object beams is the shearing direction. y The shearing direction between the third and fourth object beams is a 45-degree oblique shearing direction.
6. The measurement method of the large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing according to claim 4, characterized in that: The shearing direction x The target surface is parallel to the CCD (26) and along the horizontal direction, with the shear direction... y Parallel to the target surface of CCD (26) and along the vertical direction, the 135-degree oblique shearing direction is specifically the shearing direction on the target surface of CCD (26). x Rotate clockwise by 45 degrees, and the shearing direction at a 45-degree angle is specifically the shearing direction on the target surface of the CCD (26). x Rotate 45 degrees counterclockwise.
7. The measurement method of the large field-of-view four-directional shear speckle interferometry measurement device based on polarization multiplexing according to claim 4, characterized in that: In step 2), the spatial carrier frequency of the object light is adjusted by adjusting the relative positions of the four aperture stops in the shearing direction x and shearing direction y.