Spiral phase shifting interferometry method and system based on vortex light phase modulation

Abstract

This invention discloses a spiral phase-shifting interferometry method and system based on vortex phase modulation, which solves the problems of high cost, complex process, and low measurement accuracy in existing interferometry methods. The key technical solution includes the following steps: starting the interferometer and performing system calibration; selecting and installing a standard mirror, performing polar axis transformation on the vortex light in the reference optical path to complete phase-shifting interference and obtain the initial phase distribution information of the vortex light; replacing the standard mirror with a test mirror, similarly performing polar axis transformation on the vortex light in the reference optical path to complete phase-shifting interference and obtain the test phase distribution information of the vortex light; and extracting the wavefront phase of the test mirror by calculating the difference between the initial phase distribution information and the test phase distribution information to obtain the surface shape distribution information of the test mirror. This spiral phase-shifting interferometry method based on vortex phase modulation can improve detection accuracy and robustness, achieving higher phase modulation resolution and measurement accuracy.

Description

Technical Field

[0001] This invention relates to laser interferometry, and in particular to a spiral phase-shifting interferometry measurement method and system based on vortex light phase modulation. Background Technology

[0002] In the 1980s, Bruning et al. applied synchronous phase detection technology to optical interferometry, proposing Phase Shifting Interferometry (PSI). PSI technology, through phase demodulation of an image sequence (at least three frames), can extract wavefront phase information and reconstruct the three-dimensional morphology of the measured object's surface. PSI technology boasts advantages such as simple structure, full-field measurement, non-contact operation, high precision, high sensitivity, non-destructive testing, and fast measurement speed. After forty years of development, PSI technology has gradually replaced traditional contact detection techniques and become an important tool widely used in various measurement fields. The basic principle of PSI technology is as follows: a predetermined phase shift (or optical path) is introduced into the reference optical path (or test optical path) of the interference optical path, creating a certain phase difference between the reference and test optical paths. This means that when the phase (or optical path) changes in the optical path, the interference optical field exhibits a changing intensity distribution. In PSI multi-step phase shifting technology, multiple phase shifts are generated by phase shifters (PTZ, wavelength-tuned lasers, etc.), thereby obtaining a sequence of interference images with certain patterns using photoelectric sensors. By analyzing these image sequences with a computer, wavefront phase information can be obtained.

[0003] In the field of PSI phase extraction technology, numerous domestic scholars have conducted extensive research. In the early stages of research, classic phase-shifting algorithms such as four-step, five-step, and N-step algorithms were proposed. Subsequently, stochastic iterative least squares fitting (AIA), principal component analysis (PCA), wavelength tuning shifting algorithms, two-step phase-shifting algorithms based on Schmitt orthogonal transform (GS), and improved algorithms were further proposed. Currently, Gaussian and least squares iteration, polynomial fitting, and other algorithms have become among the cutting-edge PSI algorithms and are continuously being developed. However, while these algorithms have reached a relatively mature stage in terms of demodulation accuracy, computational speed, and detection robustness, it is worth noting that the accuracy of existing PSI technology depends on the high stability of the PSI equipment. This is mainly because existing PSI technologies generally achieve phase shifting through phase shifters, such as piezoelectric ceramic materials (PZT), micro-deformable mirrors, and micro-polarization arrays. Based on the current wavefront phase, the phase shift is introduced by repeatedly moving the phase shifter. Based on the phase-shifting principle of PSI technology, the following unavoidable disadvantages exist in its engineering applications: 1) The effectiveness of traditional PSI technology is largely limited by the inherent characteristics of phase-shifting devices such as PZT, resulting in long phase-shifting periods and low phase-shifting accuracy; 2) Traditional PSI technology is a multi-step phase-shifting technique in the time domain, with a long phase modulation period (e.g., nine-step phase-shifting), making it highly susceptible to interference from phase shifter operation and external environmental vibrations, failing to meet the requirements of dynamic environments and high-precision measurements; 3) Traditional PSI technology uses wavefront phase modulation, which cannot achieve pixel-level precise and stable phase shifting in local areas of the optical field, thus limiting its application to some extent; 4) The introduction of phase shift in traditional PSI technology directly alters the optical expression of the coherent optical field (adding a phase-shifting term), complicating the phase extraction process and limiting its application to some extent. In summary, PSI technology not only has very high requirements for the measurement environment, making the cost of achieving high-precision interferometric measurements extremely high, but also suffers from complex phase extraction processes and low measurement accuracy. Therefore, the introduction and further research of new PSI technologies, reducing dependence on experimental devices and environment, and achieving high-precision measurements are essential, which will be conducive to the promotion and application of high-precision interferometric measurement technology. Summary of the Invention

[0004] The primary objective of this invention is to provide a spiral phase-shifting interferometry measurement method based on vortex optical phase modulation, which can improve detection accuracy and robustness, and achieve higher phase modulation resolution and measurement accuracy.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0006] A spiral phase-shifting interferometry method based on vortex optical phase modulation includes the following steps:

[0007] Start the interferometer and perform system calibration;

[0008] Select and install a standard mirror, perform polar axis transformation on the vortex light in the reference optical path, complete phase-shifting interference, and extract the initial phase distribution information of the vortex light by phase extraction.

[0009] By replacing the standard mirror with the test mirror, polar axis transformation is performed on the vortex light in the reference optical path to complete phase-shifting interference and phase extraction to obtain the phase distribution information of the vortex light test.

[0010] By calculating the difference between the initial phase distribution information and the test phase distribution information, the wavefront phase of the test mirror is extracted, and the surface shape distribution information of the test mirror is obtained.

[0011] Preferably, the system correction includes field correction to make the vortex singularity coincide with the geometric center of the area array CCD.

[0012] Preferably, the vortex light in the reference optical path is phase-modulated by a liquid crystal spatial light modulator to achieve the polar axis transformation and phase shift of the vortex light.

[0013] Preferably, the topological charge of the vortex light is 1, and the polar axis transformation is a counterclockwise rotation of 0, π / 2, π, 3π / 2 to obtain four interference images with different phase shifts. The spiral phase distribution is obtained after phase extraction.

[0014] The second objective of this invention is to provide a spiral phase-shifting interferometric measurement system based on vortex light phase modulation, which can achieve phase modulation of vortex light through a liquid crystal spatial light modulator, resulting in high overall resolution and higher measurement accuracy.

[0015] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0016] A spiral phase-shifting interferometric measurement system based on vortex optical phase modulation includes:

[0017] The optical path includes a laser that generates and emits vortex light, and a half-reflective mirror that splits the vortex light into two optical paths: a test light and a reference light.

[0018] The reference optical path includes a liquid crystal spatial light modulator that performs phase modulation on the reference light, wherein the liquid crystal spatial light modulator performs polar axis transformation phase shift on the reference light;

[0019] The test optical path includes a measuring element that reflects the test light; the measuring element includes a standard mirror for initial calibration and a test element for subsequent measurements.

[0020] The imaging plane includes a CCD camera that performs interferometric imaging of a phase-modulated reference light and a reflected test light.

[0021] Preferably, the emitting optical path further includes an attenuator, a first polarizer, and a first beam expander group, which are sequentially arranged between the laser and the half-reflective mirror for vortex light adjustment.

[0022] The test optical path also includes a second beam expander group and a second polarizer, which are sequentially arranged between the semi-reflective lens and the element under test;

[0023] A neutral density filter is provided at the front end of the CCD camera in the optical path.

[0024] Preferably, the system also includes a controller coupled to the liquid crystal spatial light modulator for control, and a computer coupled to the laser, the controller, and the CCD camera.

[0025] Preferably, the laser emits vortex light with a topological charge of 1, and the singularity of the vortex light coincides with the center of the CCD array; the liquid crystal spatial light modulator performs four polar axis rotations on the reference light, which are 0, π / 2, π, and 3π / 2 counterclockwise in sequence.

[0026] In summary, the present invention has the following beneficial effects:

[0027] Phase-shifting interferometry is achieved by transforming the polar axis of vortex light, eliminating the need for traditional phase-shifting devices. This effectively avoids interference and errors caused by the phase shifter's own disturbances and hysteresis effects, thus significantly improving detection accuracy and robustness. Vortex light has a unique phase singularity and a flexible, adjustable grayscale distribution, enabling higher phase modulation resolution and measurement accuracy. Phase modulation of vortex light is achieved using a liquid crystal spatial light modulator (LC-SLM), which offers high resolution, enabling pixel-level phase modulation and higher precision measurements. This is beneficial for the promotion and application of high-precision interferometric measurement technology. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the optical path structure of the phase-shifting interferometry system.

[0029] Figure 2 This is a schematic diagram of the flow chart for this phase-shifting interferometry method;

[0030] Figure 3 A schematic diagram illustrating the introduction of phase shift amounts in traditional PSI phase shifting and vortex phase shifting methods.

[0031] Figure 4 This is a schematic diagram of the phase modulation of the rotating polar axis of a vortex.

[0032] In the diagram: 1. Computer; 2. Controller; 3. Liquid crystal spatial light modulator; 4. Test mirror; 5. First polarizer; 6. Semi-reflective mirror; 7. First beam expander group; 8. Neutral density filter; 9. CCD camera; 10. Second beam expander group; 11. Second polarizer; 12. Attenuator; 13. Laser. Detailed Implementation

[0033] A vortex beam, also known as an optical vortex, is a vortex-phase optical field with a singularity, exhibiting a ring-shaped distribution with a central dark spot. Because vortex beams carry photon orbital angular momentum (OAM), they are also called OAM beams. The complex amplitude expression for an OAM beam contains a helical phase term exp(ilθ), therefore the orbital angular momentum carried by each photon is... (l is the topological charge number, θ represents the spiral phase) This refers to Planck's constant h divided by 2π. In recent years, based on its unique orbital angular momentum characteristics, vortex beams have been widely used and promoted in fields such as information encoding, optical communication, particle capture, and micromanipulation. For PSI technology, the unique orbital angular momentum characteristics of vortex beams will bring global, pixel-level phase modulation, which means higher phase accuracy; however, there are almost no reports on the application of vortex interferometry in the field of PSI technology. This is mainly because: 1) Although the helical phase distribution of vortex light is mainly determined by the topological charge, the helical phase distribution is also directly related to the spatial position of the propagation direction. This means that controlling the topological charge alone cannot accurately achieve effective control of the helical phase distribution, and the helical phase value of each sub-wavetrain remains unknown; 2) On the other hand, the helical phase factor of vortex light increases the number of variables in the coherent optical field, and there is a nonlinear relationship between the parameters (related to the pixel spatial distribution of the CCD), which makes it impossible for existing phase extraction algorithms to achieve phase demodulation.

[0034] The present invention will be further described in detail below with reference to the accompanying drawings.

[0035] According to one or more embodiments, a spiral phase-shifting interferometry measurement system based on vortex optical phase modulation is disclosed, such as... Figure 1 As shown, it is divided into an emission optical path, a reference optical path, a test optical path, and an imaging surface. It includes a laser, a semi-reflective mirror, a liquid crystal spatial light modulator, a measuring element, and a CCD camera, sequentially arranged in the optical path. The emitted vortex light is split into two paths after passing through the semi-reflective mirror. One path forms the reference light, which reaches the liquid crystal spatial light modulator, and the other path forms the measuring light, which reaches the measuring element. The two paths are reflected back and interfere with each other before reaching the CCD camera for imaging.

[0036] It also includes a computer for setting and receiving feedback, and a controller coupled to the computer for regulating the liquid crystal spatial light modulator. The laser is also coupled to the computer, which controls the laser in the emission optical path.

[0037] In the optical transmission path, vortex light is emitted by the laser, and the vortex light with a topological charge of 1 is selected. The singularity of the vortex light coincides with the center of the CCD array. It also includes an attenuator, a first polarizer, and a first beam expander group, which are sequentially arranged between the laser and the semi-reflective mirror for vortex light adjustment.

[0038] In the reference optical path, the liquid crystal spatial light modulator (LCSLM) modulates the phase of the reference light. Vortex phase shifting is achieved through polar axis transformation. The LCSLM performs four polar axis rotations on the reference light, sequentially counterclockwise at 0, π / 2, π, and 3π / 2, obtaining interference images with different phase shifts. The LCSLM is matched and controlled by an LC-SLM controller to achieve the output of its control voltage. Precise control and feedback reception are achieved through a computer.

[0039] The test optical path also includes a second beam expander group and a second polarizer, which are sequentially arranged between the semi-reflective mirror and the device under test (DUT). The measuring elements include a standard mirror for initial calibration and the DUT for subsequent measurements based on actual conditions.

[0040] The CCD camera forms an imaging surface, acquiring phase-modulated reference light and reflected test light through interference imaging. A neutral density filter is placed at the front end of the CCD camera in the optical path.

[0041] During implementation, the following equipment can be used for the vortex phase-shifting interferometer:

[0042] Computer: Advantech IPC-610L-701VG, Intel i5-2400 processor, supports JPEG hardware encoding and decoding, 4GB DDR3 memory. Supports RGB 24-bit interface and TVOUT video output. Monitor: Samsung C27F390FHC, 1920*1080 resolution.

[0043] LC-SLM controller: Matched with a liquid crystal spatial light modulator (LC-SLM), it can output the control voltage of the liquid crystal spatial light modulator (LC-SLM);

[0044] Liquid Crystal Spatial Light Modulator (LC-SLM): Resolution 1920x1152, light energy utilization efficiency 88%, liquid crystal response speed 833Hz, selectable wavelength range 400nm-1650nm, effectively eliminates phase ripple, fast liquid crystal response speed, phase modulation up to 6π, high damage threshold, and can realize pure phase modulation, pure amplitude modulation, and mixed phase and amplitude modulation.

[0045] Test mirror: Select according to the actual situation;

[0046] First polarizer and second polarizer: Daheng GCL-0510 series linear thin film polarizers, diameter: 25.4 mm (+00 / -0.1 mm), clear aperture: φ10 mm, thickness: 5 + 0.1 mm, wavefront distortion: < λ / 4 @ 633 nm, surface finish: grade I, operating temperature: -20~+120 °C;

[0047] Half-reflecting and half-transmitting lens: Daheng GCC-4011 series broadband beam splitting prisms, transmittance / reflection ratio: 50 / 50; material K9; outer dimension: 25.4 mm * 25.4 mm * 25.4 mm;

[0048] First beam expander group and second beam expander group: Daheng GCO-140 series laser beam expanders, beam expansion ratio 8×, clear aperture 10.5 mm;

[0049] Neutral filter: neutral density filter, diameter D = 25 mm, optical density value = 4.0, gray glass OD value 2, D = 25 mm, effective aperture: 90%;

[0050] CCD camera: using Basler acA2400-50gm area array CCD, 2048 * 1536 pixels, imaging area size is 3626 μm x 2709 μm, pixel size is 1.75 μm x 1.75 μm, maximum speed can reach 50 frames per second;

[0051] Attenuator: model GT-060101, rotary adjustment, adjustable attenuator, optical density OD: 0 - 3.0;

[0052] Laser: wavelength 532 nm, 200 mw solid laser, single longitudinal mode.

[0053] According to one or more embodiments, a spiral phase-shifting interference measurement method based on vortex light phase modulation is disclosed. As Figure 2 shown, it includes the following steps:

[0054] Start the interferometer and perform system calibration.

[0055] Select and install the reference mirror, perform polar axis transformation on the vortex light in the reference optical path, complete phase-shifting interference, and extract the phase to obtain the initial phase distribution information of the vortex light. Rotate the polar axis of the vortex light in the reference optical path by (0, π / 2, π, 3π / 2) through the LC-SLM. The modulation of the LC-SLM is in the phase modulation mode, and four frames of interference images I s，0 (x,y), I s，1 (x,y); I s，2 (x,y), I s，3(x,y); the initial spiral phase distribution θ0(x,y) is obtained by phase extraction. A vortex beam with a topological charge of 1 is selected, and the singularity of the vortex beam coincides with the center of the CCD array. The polar axis is rotated counterclockwise by 0, π / 2, π, and 3π / 2 in sequence to obtain interference images with different phase shifts.

[0056] Replacing the standard mirror with the test mirror, a polar axis transformation is performed on the vortex light in the reference optical path to complete phase-shifting interference. Phase extraction is then used to obtain the phase distribution information of the vortex light test. The polar axis of the vortex light in the reference optical path is rotated (0, π / 2, π, 3π / 2) using LC-SLM, obtaining four interference images I0(x,y), I1(x,y); I2(x,y), I3(x,y). Phase extraction yields the initial spiral phase and the sum of the phase distributions of the test mirror surface.

[0057] By calculating the difference between the initial phase distribution information and the test phase distribution information, the wavefront phase of the test mirror is extracted, and the surface shape distribution information of the test mirror is obtained. Based on the obtained initial spiral phase distribution θ0(x,y), the phase distribution of the test mirror surface shape can be obtained through difference operations.

[0058] The cross-section of a vortex beam exhibits an anisotropic polarization distribution in a vortex shape and carries orbital angular momentum; it is a dark, hollow beam with a continuous spiral phase. The vortex-shaped phase distribution of the beam is determined by the phase factor. Therefore, after vortex phase modulation, the phase shift lθ at any point (x,y) on the CCD is determined. n (x,y) and This direct correlation indicates that the vortex-based phase-shifting technique is a global, differential phase modulation. Therefore, the phase shift at any point (x, y) on the CCD after phase modulation is lθ. n (x, y), its expression is:

[0059]

[0060] In the formula, a(x,y) and b(x,y) represent the background light intensity and modulation degree, respectively; The phase to be measured is represented by . n and N represent the current acquisition frame number and the total number of acquisition frames, respectively. l is the topological charge number, and θ represents the polar angle. Vortex light is based on its unique spiral phase term. To achieve preset phase modulation, traditional PSI phase shifting and vortex phase shifting methods, for example... Figure 3 As shown, Figure 3 The left-hand side diagram shows the introduction of phase shift in traditional PSI, and the right-hand side diagram shows the introduction of phase shift in vortex phase shift.

[0061] In traditional PSI technology, phase information is represented by the pixel grayscale of a CCD. This means that the spatial position of the phase is defined by the pixel coordinates of the CCD, i.e., a Cartesian coordinate system on a plane. However, for vortex light, its helical phase value is determined by both the topological charge and the polar angle. Therefore, the phase of vortex light is represented in a polar coordinate system on a plane. According to the transformation relationship between the two-dimensional Cartesian coordinate system and the polar coordinate system, if the origin of the Cartesian coordinate system is (x0, y0), and the origins of the two coordinate systems coincide, the polar coordinates of a pixel with spatial coordinates (x0, y0) can be denoted as:

[0062]

[0063] In the formula, r represents the polar radius and θ represents the polar angle. Let the topological charge l be 1, and draw a vortex beam with the origin (x0, y0) as the center, in pixels, and with the polar radius as the radius. Its phase varies from 0 to 2π. A schematic diagram of its principle is shown below. Figure 4 As shown on the left. If the light intensity of pixel (x, y) is: In polar coordinates, the coordinates are (x A ,y A The spiral phase is θ. A Given a pixel A with a constant polar radius, there exists a pixel B (with coordinates (x...)) that differs from the pixel A by α in the counterclockwise direction. B ,y B (See diagram 4(middle)). And coordinate B can be represented as: According to the law of cosines, the distance L between pixels A and B is... AB It can be recorded as:

[0064]

[0065] Furthermore, it is assumed that the vortex polar coordinate axis is rotated counterclockwise by an angle β (e.g., Figure 4 (Right) Pixel A moves to pixel C, and the coordinates of C are (x...). C ,y C The spiral phase is θ. C Then it exists:

[0066]

[0067] Similarly, the distance L between pixels A and C AC It can be represented as:

[0068]

[0069] therefore,

[0070]

[0071] If true, then the vortex phase shift is equal to the rotation angle of the polar coordinate axis, meaning that pixels C and B are the same point. This implies that pixel phase modulation can be achieved by rotating the polar axis of the vortex, and when the topological charge l = 1, the rotation angle of the polar coordinate axis is equal to the vortex phase shift.

[0072] The initial phase calibration process for vortex light is as follows:

[0073] Using the aforementioned vortex phase modulation method, with the polar axis position as the starting line, the polar axis is rotated sequentially by angles of 0, π / 2, π, and 3π / 2, and four frames of interference images are acquired sequentially. The light intensity of the interference images can then be recorded as:

[0074]

[0075] In the formula, θ0(x,y) represents the spiral phase distribution. The phase of the wavefront to be measured is introduced to the surface under test. In the actual measurement process, the background light intensity term 'a' in the above equation... i (x,y) and modulation b i Since (x, y) are invariants, if a high-precision standard plane mirror is used as the element under test, the corresponding optical expression is:

[0076]

[0077] Therefore, based on the triangular relationship, the above equation transforms into:

[0078]

[0079] Since both the test mirror and the reference mirror are standard plane mirrors, It tends to 0. Therefore, the initial spiral phase θ0(x,y) can be expressed as:

[0080]

[0081] In the formula, R1 represents the wrap phase of the standard plane mirror.

[0082] After the initial spiral phase calibration of the system, the component under test is replaced with the actual test mirror. Similarly, after polar axis conversion, the image light intensity is:

[0083]

[0084] Based on trigonometric relationships and arctangent operations, the above formula can be written as:

[0085]

[0086] In the formula, R2 represents the actual test package phase. Let R1 be the phase of the element under test; θ0(x,y) be the initial spiral phase; based on the obtained phase distributions R1 and R2, after unwrapping operations and Zernike fitting to eliminate tilt terms, accurate initial phase distributions R of the spiral beam can be obtained respectively. 1zernike and the actual test phase distribution R 2zernike R 2zernike Includes the initial phase distribution R of the spiral beam 1zernike Therefore, after the difference calculation, the actual test mirror can be obtained. The phase distribution, i.e.:

[0087]

[0088] This indicates the phase distribution of the surface shape of the element under test.

[0089] Accurate phase modulation and wavefront phase information demodulation can be achieved through vortex phase shifting. The proposed vortex phase shifting method is realized through vortex optical polar axis transformation, eliminating the need for traditional phase shifting devices (such as PZT), thus effectively avoiding interference and errors caused by phase shifter self-disturbance and hysteresis effect, improving detection accuracy and robustness. Vortex light has a special phase singularity and a flexible and adjustable grayscale distribution, which can achieve higher phase modulation resolution and measurement accuracy. The phase modulation of vortex light can be achieved using a liquid crystal spatial light modulator (LC-SLM), which has high resolution and can achieve pixel-level phase modulation and higher precision measurement.

[0090] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A spiral phase-shifting interferometry method based on vortex optical phase modulation, characterized in that, It includes the following steps: Start the interferometer and perform system calibration, which includes field calibration to make the vortex singularity coincide with the geometric center of the CCD array. Select and install a standard mirror, and use a liquid crystal spatial light modulator to perform phase modulation on the vortex light in the reference optical path, so that the polar axis of the vortex light is rotated counterclockwise by 0, π / 2, π, and 3π / 2 in sequence to obtain four frames of interference images. Then, use a phase-shifting algorithm to extract the phase and obtain the initial phase distribution information of the vortex light. The standard mirror was replaced with the test mirror, and the vortex light in the reference optical path was also phase-modulated by the liquid crystal spatial light modulator. The polar axis of the vortex light was rotated counterclockwise by 0, π / 2, π, and 3π / 2 in sequence to obtain four frames of interference images. The phase was extracted using the phase-shifting algorithm to obtain the phase distribution information of the vortex light test. By calculating the difference between the initial phase distribution information and the test phase distribution information, the wavefront phase of the test mirror is extracted, and the surface shape distribution information of the test mirror is obtained.

2. A spiral phase-shifting interferometric measurement system based on vortex optical phase modulation. Its characteristics include: The optical path includes a laser that generates and emits vortex light, a half-reflective mirror that splits the vortex light into two optical paths, a test beam and a reference beam, and is used to emit vortex light with a topological charge of 1. The reference optical path includes a liquid crystal spatial light modulator that performs phase modulation on the reference light, wherein the liquid crystal spatial light modulator performs polar axis transformation phase shift on the reference light; The test optical path includes a measuring element that reflects the test light; the measuring element includes a standard mirror for initial calibration and a test element for subsequent measurements. The imaging plane includes a CCD camera that performs interferometric imaging of the phase-modulated reference light and the reflected test light, and is used to receive the reference light and the test light and form an interferometric image. It also includes a controller and a computer, the computer being coupled to a liquid crystal spatial light modulator, a laser, and a CCD camera, for executing phase-shifting algorithms and outputting test results, specifically: The phase of the vortex light in the reference optical path is modulated by a liquid crystal spatial light modulator, so that the polar axis of the vortex light is rotated counterclockwise by 0, π / 2, π, and 3π / 2 in sequence to obtain four frames of interference images. The phase is extracted by a phase shifting algorithm to obtain the initial phase distribution information and the test phase distribution information of the vortex light. By calculating the difference between the initial phase distribution information and the test phase distribution information, the wavefront phase of the test mirror is extracted, and the surface shape distribution information of the test mirror is obtained.

3. The spiral phase-shifting interferometric measurement system based on vortex optical phase modulation according to claim 2, characterized in that: The optical path also includes an attenuator, a first polarizer, and a first beam expander group, which are sequentially arranged between the laser and the half-reflective mirror for vortex light adjustment. The test optical path also includes a second beam expander group and a second polarizer, which are sequentially arranged between the semi-reflective lens and the element under test; A neutral density filter is provided at the front end of the CCD camera in the optical path.

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