A dynamic phase shift interferometry system and method thereof

Abstract

The application discloses a kind of dynamic phase shift interferometry system and method thereof, including first depolarization beam splitter, first depolarization beam splitter side is sequentially spaced with first polarizer, collimating lens, pinhole filter, first attenuator and laser, the other side is sequentially spaced with third polarizer and object, the upside of first depolarization beam splitter is sequentially spaced with second polarizer, second attenuator and first mirror, the downside of first depolarization beam splitter is sequentially spaced with imaging lens, second depolarization beam splitter, polarization grating and second mirror, the side of second depolarization beam splitter is provided with camera;Polarization grating is liquid crystal circular polarization grating, liquid crystal molecule fast axis orientation is periodic continuous gradual change along x direction, overall has λ / 2 phase delay amount.The application can ensure high-precision phase measurement results while meeting the demand of dynamic measurement.

Description

Technical Field

[0001] This invention belongs to the field of high-precision dynamic interferometry technology, specifically relating to a dynamic phase-shifting interferometry system and method. Background Technology

[0002] In numerous engineering, medical, and military fields, high-precision dynamic measurement of the topography and deformation of optical or non-optical surfaces across the entire field is crucial for ensuring system machining accuracy and analyzing the mechanical properties of parts. It plays a vital role in maintaining system safety, evaluating production quality, and optimizing system design. Interferometry, as a full-field, non-contact measurement method, offers wavelength-level theoretical detection accuracy, guaranteeing the accuracy of measurement results and possessing unparalleled advantages over other technologies in the field of high-precision measurement.

[0003] To improve the practical measurement accuracy of interferometry, in 1974, scholars proposed the time-phase-shifting interferometry method. This method introduces a specific phase shift between beams to establish a phase-modulated interference sequence, thereby solving for the phase and intensity information in the interference fringe pattern. However, limited by the time-phase-shifting process, this technique is not suitable for dynamic measurement scenarios, thus leading to the development of the spatial phase-shifting interferometry method (also known as the synchronous phase-shifting interferometry method). Spatial phase-shifting interferometry can acquire multiple phase-shifting interference fringe patterns simultaneously, thereby extracting the phase parameters to be measured and achieving interferometry of dynamic targets. This method has broad application prospects in optical processing, astronomy, and defense, especially in unstable measurement scenarios with time-varying factors such as vibration, turbulence, and temperature drift, where its advantages are even more prominent. The key to realizing spatial phase-shifting interferometry lies in spatially splitting a pair of coherent beams and simultaneously introducing corresponding phase modulation. Existing methods are mainly based on polarization phase-shifting schemes.

[0004] The key to establishing spatial phase-shifting technology lies in achieving spatial beam splitting and generating synchronous phase shift. This can be achieved by utilizing the polarization characteristics of light waves to modulate the polarization of the reference and object beams. There are two main beam splitting methods: one is based on a beam-splitting prism. This method uses a beam-splitting prism to split a pair of orthogonally polarized reference and test beams. Different phase shifts are then introduced in each orthogonal path using polarization devices. Multiple phase-shifted interference fringes are simultaneously acquired using multiple cameras or a single camera to achieve spatial phase-shifted interferometry. However, this method has two problems: firstly, the split beams pass through different optical paths, causing inconsistent effects on the interference field. For example, different mirrors introduce different jitter and distortion. Secondly, the beam-splitting prism alters the beam polarization state to some extent. Both of these issues affect the consistency of phase shift within and between frames, as well as the consistency of background intensity in the phase-shifted interference sequence, thus reducing measurement accuracy.

[0005] Another method of beam splitting utilizes the diffraction properties of light. This involves filtering out multiple orthogonally polarized beams in one direction using diffraction elements. In each split, a polarization device modulates the phase, and a single camera captures multiple phase-shifted interference fringes to achieve spatial phase-shifted interferometry. In this method, the optical systems through which each beam passes are essentially identical, thus overcoming the problems of prism-based beam splitting. However, it also has drawbacks. First, there is a decrease in light energy utilization. After passing through the diffraction element, the beam generates multiple diffraction orders, but typically only 2-4 beams are phase-modulated (forming 2-4 phase-shifted interference fields), while the remaining orders are wasted. Second, the beam splitting and phase-shifting processes are independent and occur sequentially. The polarization modulation device (usually a polarization array) needs to be registered to the position of each beam, and it needs to be re-fabricated for different aperture sizes and camera sizes, increasing system costs. Furthermore, the extinction ratio of such a small polarization array is usually worse than that of a single linear polarizer, leading to problems such as inaccurate phase modulation and inconsistent background light intensity, reducing measurement accuracy.

[0006] In summary, the challenge of achieving high-precision dynamic interferometry based on polarization spatial phase shift lies in efficient beam splitting methods and precise phase shift modulation, so as to meet the dynamic measurement requirements while ensuring high-precision phase measurement results. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a dynamic phase shift interferometry system and method to address the shortcomings of the prior art, thereby solving the technical problem of the influence of environmental interference and optical component defects on the phase shift.

[0008] The present invention adopts the following technical solution:

[0009] A dynamic phase-shift interferometry method includes the following steps:

[0010] S1. The first depolarizing beam splitter splits the beam into an object beam and a reference beam while maintaining the polarization state of the beam unchanged. The object beam and the reference beam are reflected and then combined by the first depolarizing beam splitter, and then simultaneously incident perpendicularly on the polarization grating.

[0011] S2. When the incident light is linearly polarized, the outgoing light on the other side of the polarization grating is ±1 order left-handed and right-handed circularly polarized light with an energy ratio of 1:1; when the incident light is circularly polarized, the outgoing light on the other side of the polarization grating contains only a single beam with the opposite rotation direction to the incident light.

[0012] S3. Based on the simultaneous generation of two phase-shifted interference fields in step S2, control the relative distance between the interference fields and simultaneously record two phase-shifted interference fringe patterns on the same camera target surface.

[0013] S4. When the object under test is an optical surface, register the pixels of the two phase-shifting interferometric fringe patterns obtained in step S3, and solve for the phase based on the two phase-shifting interferometric fringe patterns to complete the dynamic phase-shifting interferometry.

[0014] S5. When the object being measured has a rough surface, perform high-precision dynamic phase measurement on the deformation of the rough surface.

[0015] Preferably, in step S1, the polarization directions of the reference light and the object light are adjusted to 45° and 0° respectively using the second polarizer and the third polarizer.

[0016] More preferably, for a reference light with 45° linear polarization, the optical field distribution E formed after modulation by a polarization grating is... r2 for:

[0017]

[0018] Among them, i 2 =-1,E r1 E is the complex amplitude of the 45° polarized reference light. r The initial complex amplitude of the reference light is φ, and the grating phase is φ.

[0019] For a linearly polarized object light at 0°, the complex amplitude distribution E of the optical field after passing through a polarization grating o2 for:

[0020]

[0021] Among them, E o The initial complex amplitude of the object light.

[0022] More preferably, the left-hand and right-hand polarization components in the reference light and the object light interfere with each other, forming two interference field intensity distributions I1 and I2, respectively:

[0023]

[0024]

[0025] Among them, A o Let A be the amplitude of the object light. r As a reference light amplitude, The phase of the object light, The phase of the reference light.

[0026] Preferably, in step S3, the second reflector is used as the grating projection surface. The outgoing light of the polarization grating is reflected by the second reflector and then passes through the polarization grating again. At this time, the spacing of the outgoing light is d = 2 m, and it is reflected to the target surface of the camera by the second depolarizing beam splitter. m is the spacing of the outgoing light before it is reflected by the reflector.

[0027] More preferably, the emitted light spacing m is:

[0028] m=2·s·tanθ

[0029] Where s represents the distance between the grating and the projection surface; θ represents the deflection angle of the emitted light.

[0030] Preferably, step S4 specifically includes:

[0031] The reference light is blocked, and only the intensity distributions I1 and I2 of the object light are collected. The intensity map is then binarized. Then, according to the shape of the imaging aperture, two regions that match it are searched in the binarized image, and the centroid coordinates (x1, y1) and (x2, y2) of the intensity values ​​in the corresponding regions are calculated as the basis for establishing the pixel coordinate transformation relationship of the interference field map. The phase is solved based on the two-frame phase-shifted interference fringe map.

[0032] More preferably, the correspondence between pixel coordinates between two interference field sequences within a single frame of a camera image is expressed as follows:

[0033] I2(m,n)=I1(u+Δx,v+Δy)

[0034] Where (u,v) and (m,n) correspond to the pixel coordinates of I1 and I2, and (Δx,Δy) is the coordinate difference.

[0035] Preferably, step S5 specifically includes:

[0036] Pixel alignment was performed on the phase-shifted interferometry sequences of the object before and after deformation to obtain a three-step phase-shifted fringe pattern containing the surface deformation phase. Multi-frame phase-shift demodulation was then used to obtain the deformation phase information. The actual deformation Δz is obtained after conversion of the enclosed phase diagram. Another technical solution of the present invention is a dynamic phase-shift interferometry measurement system, which utilizes the aforementioned dynamic phase-shift interferometry measurement method, including a first depolarizing beam splitter. On one side of the first depolarizing beam splitter, a first polarizer, a collimating lens, a pinhole filter, a first attenuator, and a laser are sequentially spaced. On the other side, a third polarizer and an object are sequentially spaced. On the upper side of the first depolarizing beam splitter, a second polarizer, a second attenuator, and a first reflector are sequentially spaced. On the lower side of the first depolarizing beam splitter, an imaging lens, a second depolarizing beam splitter, a polarizing grating, and a second reflector are sequentially spaced. A camera is disposed on one side of the second depolarizing beam splitter. The polarizing grating is a liquid crystal circular polarizing grating, in which the fast axis orientation of the liquid crystal molecules changes periodically and continuously along the x-direction, and the whole has a phase delay of λ / 2.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] A dynamic phase-shift interferometry method utilizes the synchronous polarization-phase modulation capability of a liquid crystal circular polarization grating to incident linearly polarized light. By adjusting the polarization states of the object light and reference light to 0° and 45° linear polarization respectively, and synchronously incident on the polarization grating, two interference fields with a 90° phase shift are generated. These interference fields are independently separated, ultimately achieving single-frame synchronous recording of the phase-shift interferogram sequence. This invention features a simple and compact structure, improving the applicability of the measurement method in various applications. It also avoids the influence of environmental interference on the phase shift, ensuring the accuracy of phase shift demodulation calculation and achieving high-precision interferometry. It can perform high-precision quantitative phase imaging on optical surfaces and also conduct full-field, high-precision dynamic deformation measurement on rough surfaces, meeting the real-time and accuracy requirements of various precision measurement applications.

[0039] A high-precision dynamic phase-shift interferometry measurement system based on a liquid crystal circularly polarized grating was constructed. The laser light, after beam expansion and collimation, forms a plane wave illumination. Second and third polarizers are used to adjust the polarization directions of the reference and object beams to 45° and 0°, respectively, and then the beams are combined by a first depolarizing beam splitter, simultaneously incident perpendicularly on the polarization grating. The purpose is twofold: firstly, to ensure that the reference and object beams are simultaneously polarized by the grating, each forming left-handed and right-handed circularly polarized light, thus generating two interference fields; secondly, to utilize the difference in polarization angles between the reference and object beams and the phase modulation effect of the circularly polarized grating on beams with different linear polarization angles, ensuring a stable 90° phase shift between the two interference fields.

[0040] A combination of a second depolarizing beam splitter and a second reflecting mirror is used to rationally control the relative distance between the interference fields, i.e., the spacing between the outgoing beams of the polarization grating, to adapt to different imaging field ranges or system imaging apertures. The second reflecting mirror is the projection surface of the grating. The outgoing beams of the polarization grating are reflected by the second reflecting mirror and then pass through the polarization grating again. At this point, the spacing d of the outgoing beams (dashed arrow) is 2 m, and they are reflected by the second depolarizing beam splitter to the camera target surface. The position of the camera depends on the rear focal plane of the imaging lens. The advantage of this design is that the interference field spacing d can be adjusted by changing the axial position of the second reflecting mirror. The adjustment process does not affect the imaging effect and always ensures the conjugate positional relationship between the object being measured and the camera.

[0041] Based on the system and method design of this invention, two phase-shifting interference fringe patterns can be recorded simultaneously on the same camera target surface, realizing two-frame synchronous phase-shifting interferometry based on a liquid crystal circular polarization grating. This achieves the purpose of dynamic measurement.

[0042] After the measurement system is set up, the reference light is blocked, and only the intensity distribution of the object light is collected, with the aim of achieving high-precision pixel position registration. First, the intensity map is binarized. Then, according to the shape of the imaging aperture, two regions that match it are searched in the binarized image, and the centroid coordinates (x1, y1) and (x2, y2) of the intensity values ​​in the corresponding regions are calculated as the basis for establishing the pixel coordinate transformation relationship of the interferometric field map.

[0043] Quantitative phase imaging can be directly deployed for optical surface objects. However, to solve for the dynamic deformation of rough surfaces, it is necessary to analyze the phase-shifted speckle interferograms (I) acquired before and after deformation. b1 I b2 and I d1 I d2 By performing pairwise subtraction operations, three-frame phase-shifted fringe patterns corresponding to the out-of-plane deformation are obtained. Using a multi-frame phase-shift demodulation algorithm, deformation phase information with high accuracy and low speckle noise can be obtained, which can then be converted into actual deformation amount, ensuring the accuracy of deformation measurement.

[0044] A dynamic phase-shifting interferometric measurement system is characterized by its simple and compact structure. It can perform high-precision quantitative phase imaging on optical surfaces and also conduct full-field, high-precision dynamic deformation measurement on rough surface objects, meeting the real-time and accuracy requirements of various precision measurement applications.

[0045] In summary, this invention utilizes the synchronous polarization-phase modulation capability of a liquid crystal circular polarization grating for incident linearly polarized light. By rationally designing the polarization states of the reference and object lights in the interferometric measurement system, it achieves single-frame synchronous recording of phase-shifted interferogram sequences. Both the replication of the interferometric light field and phase modulation are accomplished by the polarization grating, simplifying the interferometric system structure, eliminating the need for optical field alignment between the grating, polarization array, and camera dimensions, and improving the applicability of the measurement method in different applications. Simultaneously, it avoids the influence of environmental interference on the phase shift, ensuring the accuracy of phase shift demodulation calculations and achieving high-precision interferometric measurement.

[0046] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the optical path of the measurement system of the present invention;

[0048] Figure 2 This is a schematic diagram of the phase-shifting interference field spacing adjustment method based on the combination of polarization grating and mirror in the system;

[0049] Figure 3 A two-step phase-shifted fringe pattern captured by the camera in a single frame;

[0050] Figure 4This is a schematic diagram of pixel coordinate registration based on the binarized light intensity map;

[0051] Figure 5 This is a flowchart of the measurement process of the present invention;

[0052] Figure 6 This is a high-precision quantitative phase imaging result of an optical surface engraved with the letters XJTU;

[0053] Figure 7 This provides high-precision phase measurement results for the dynamic deformation of rough surfaces.

[0054] Wherein: 1. Laser; 2. First attenuator; 3. Pinhole filter; 4. Collimating lens; 5. First polarizer; 6. First depolarizing beam splitter; 7. Second polarizer; 8. Second attenuator; 9. First reflector; 10. Third polarizer; 11. Object under test; 12. Imaging lens; 13. Camera; 14. Second depolarizing beam splitter; 15. Polarizing grating; 16. Second reflector. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0057] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0058] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0059] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0060] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0061] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0062] This invention provides a dynamic phase-shift interferometry system and method. By adjusting the polarization states of the object light and reference light to 0° and 45° linearly polarized light, respectively, and utilizing the synchronous polarization-phase modulation capability of the incident linearly polarized light by a liquid crystal circular polarization grating, two interference fields with a 90° phase shift are generated. These interference fields are independently separated, enabling single-frame synchronous recording of a phase-shifted interference fringe sequence. The replication of the interference field and phase modulation are both accomplished by the polarization grating, achieving integrated beam splitting and phase shift synchronization. This simplifies the interference system structure, eliminating the need for optical field alignment between the grating, polarization array, and camera dimensions, improving the applicability of the measurement method in different applications, increasing light energy utilization, and avoiding the influence of environmental interference and optical component defects on the phase shift, ensuring the accuracy of phase shift demodulation calculation and achieving high-precision interferometry. The entire system and method are characterized by simple and compact structure, capable of high-precision quantitative phase imaging of optical surfaces, and also capable of full-field, high-precision dynamic deformation measurement of rough surface objects, meeting the real-time and accuracy requirements of various precision measurement applications.

[0063] Please see Figure 1 The present invention discloses a dynamic phase-shifting interferometric measurement system, comprising a laser 1, a first attenuator 2, a pinhole filter 3, a collimating lens 4, a first polarizer 5, a first depolarizing beam splitter 6, a second polarizer 7, a second attenuator 8, a first reflecting mirror 9, a third polarizer 10, an object 11, an imaging lens 12, a camera 13, a second depolarizing beam splitter 14, a polarizing grating 15, and a second reflecting mirror 16.

[0064] The first depolarizing beam splitter 6 has a first polarizer 5, a collimating lens 4, a pinhole filter 3, a first attenuator 2 and a laser 1 arranged sequentially on one side, and a third polarizer 10 and an object 11 arranged sequentially on the other side. The first depolarizing beam splitter 6 has a second polarizer 7, a second attenuator 8 and a first reflector 9 arranged sequentially on the upper side, and an imaging lens 12, a second depolarizing beam splitter 14, a polarizing grating 15 and a second reflector 16 arranged sequentially on the lower side. A camera 13 is arranged on one side of the second depolarizing beam splitter 14.

[0065] The light emitted by laser 1 is expanded and collimated to form a plane wave. The first polarizer 5 is used to control the polarization state of the light source, and the second polarizer 7 and the third polarizer 10 are used to adjust the polarization directions of the reference light and the object light to 45° and 0°, respectively.

[0066] The second attenuator 8 can control the intensity of the reference light and match it with the intensity of the object light to produce high-contrast interference fringes.

[0067] After the reference light and object light are reflected by the first reflecting mirror 9 and the object under test 11, they are combined by the first depolarizing beam splitter 6. At this time, the linearly polarized reference light and object light are simultaneously incident perpendicularly on the polarization grating 15. The liquid crystal circular polarization grating 15 is a geometric phase element that can split the energy beam according to the polarization state of the incident light. The fast axis orientation of the liquid crystal molecules is periodically and continuously changed along the x-direction, and the whole has a phase delay of λ / 2.

[0068] Please see Figure 5 The present invention provides a dynamic phase-shift interferometry measurement method, comprising the following steps:

[0069] S1. The light emitted by laser 1 is expanded and collimated to form a plane wave. The first polarizer 5 is used to control the polarization state of the light source. The first depolarizing beam splitter 6 splits the beam into object light and reference light while maintaining the polarization state of the beam unchanged. The second polarizer 7 and the third polarizer 10 are used to adjust the polarization directions of the reference light and object light to 45° and 0°, respectively. The second attenuator 8 can control the intensity of the reference light and match it with the intensity of the object light to produce high-contrast interference fringes. After the two beams are reflected by the first reflecting mirror 9 and the object under test 11, they are combined by the first depolarizing beam splitter 6. At this time, the linearly polarized reference light and object light are simultaneously incident perpendicularly on the polarization grating 15.

[0070] Based on the Jones matrix, with reference light E r1 、physical light E o1 The complex amplitudes are expressed as follows:

[0071]

[0072]

[0073] in, A o A r , These represent the amplitude and phase of the object beam and the reference beam, respectively.

[0074] S2. When the incident light is linearly polarized, the outgoing light on the other side of the polarization grating 15 is ±1 order left-handed and right-handed circularly polarized light with an energy ratio of 1:1; when the incident light is circularly polarized, the outgoing light on the other side of the polarization grating 15 contains only a single beam with the opposite polarization direction to the incident light; thus, it has the function of simultaneously replicating and splitting the incident beam and modulating its polarization.

[0075] The Jones matrix of the liquid crystal circular polarization grating 15 is expressed as:

[0076]

[0077] Where φ represents the grating phase.

[0078] For a reference light with 45° linear polarization, the light field distribution formed after modulation by the polarization grating is as follows:

[0079]

[0080] Among them, i 2 =-1,

[0081] Similarly, the complex amplitude distribution of the optical field after the object light with 0° linear polarization passes through the polarization grating is:

[0082]

[0083] in,

[0084] At this point, the left-hand and right-hand polarization components of the reference light and the object light interfere with each other, and the intensity distributions of the two interference fields formed are expressed as follows:

[0085]

[0086]

[0087] As can be seen from the above equation, there is a fixed phase difference between the two interference fields, i.e., the phase shift is... This enabled two-frame synchronous phase-shift interferometry based on a liquid crystal circular polarization grating.

[0088] S3. Based on the simultaneous generation of two phase-shifted interference fields in step S2, in order to record two interference fringe patterns on the same camera target surface and achieve the purpose of dynamic measurement, it is necessary to reasonably control the relative distance between the interference fields, i.e. the ±1st order output light spacing of the polarization grating.

[0089] Please see Figure 2 The spacing between the emitted beams (solid arrows) is represented as follows:

[0090] m=2·s·tanθ

[0091] Where s represents the distance between the grating and the projection surface; θ represents the deflection angle of the outgoing light, which depends on the grating phase period p and the incident light wavelength λ, as follows:

[0092]

[0093] With the polarization grating parameters fixed, in order to adapt to different imaging field ranges or system imaging apertures, it is necessary to flexibly adjust the spacing of the interference field by changing s. However, if the target surface of the camera 13 is set as the projection surface (i.e., the camera 13 is placed directly behind the polarization grating 15), m can only be adjusted by changing the position of the grating (along the optical axis), and the adjustment range is limited by the back focal length of the imaging system.

[0094] Therefore, a second depolarizing beam splitter 14 and a second reflecting mirror 16 are added to the system. The second reflecting mirror 16 is the grating projection surface. The outgoing light from the polarizing grating 15 is reflected by the second reflecting mirror 16 and then passes through the polarizing grating 15 again. At this time, the spacing d of the outgoing light (dashed arrow) is 2 m, and it is reflected by the second depolarizing beam splitter 14 to the target surface of the camera 13. m is the spacing of the outgoing light before it is reflected by the reflecting mirror.

[0095] The position of the camera 13 depends on the rear focal plane of the imaging lens. The advantage of this design is that the interference field spacing d can be adjusted by changing the axial position of the second reflecting mirror 16. The adjustment process does not affect the imaging effect and can always ensure the conjugate position relationship between the object and the camera.

[0096] Please see Figure 3 The light intensity distribution of the interference field acquired by the camera in a single exposure is divided into two parts, which correspond to two phase-shifted interference fringe patterns of the object under the same state, which is consistent with the theoretical analysis. The phase information related to the measured surface is obtained by using the phase demodulation and unwrapping algorithm of the two phase-shifted interference fringes, thereby achieving the purpose of high-precision dynamic measurement.

[0097] Dynamic phase measurement

[0098] When the object under test 11 is an optical surface, the present invention can perform high-precision dynamic interferometric quantitative phase imaging on it, and the measurement steps are as follows: steps S4 and S5.

[0099] When the object being measured 11 has a rough surface, the present invention can perform high-precision dynamic phase measurement of its deformation.

[0100] Before the measured object 11 deforms, the intensity distribution of the phase-shifted interference fringe pattern acquired by the camera in a single acquisition is represented as follows:

[0101]

[0102]

[0103] When the measured object 11 deforms, the following occurs:

[0104]

[0105]

[0106] Based on the pixel coordinate registration method in step S4, pixel alignment is performed on the phase-shifted interference sequence images before and after deformation. Then, the interference intensity images before and after deformation are subtracted pairwise to obtain a three-step phase-shifted fringe pattern containing the surface deformation phase.

[0107]

[0108]

[0109]

[0110] The phase shift between the three phase-shifted fringe patterns is Based on this, a multi-frame phase-shift demodulation method is used to obtain information containing deformed phase information. The package phase diagram.

[0111] There are many multi-frame phase-shift demodulation methods employed. In this measurement example, a matrix decomposition-based demodulation method is used, and the phase expansion method is a Zernike polynomial fitting-based phase expansion method. After obtaining the expanded phase, the phase measurement result is converted into the actual deformation Δz according to the following formula:

[0112]

[0113] S4. Pixel registration of two phase-shifted interferometric fringe patterns

[0114] A single-exposure image captured by a camera simultaneously contains two phase-shifted interference fringe patterns; therefore, high-precision pixel registration is a crucial prerequisite for two-frame phase-shifted demodulation. This invention employs a pixel matching method based on the centroid of an intensity map. After the measurement system is established, the reference light is blocked, and only the object light intensity distribution is acquired, such as... Figure 4 As shown.

[0115] First, the intensity map is binarized; then, based on the shape of the imaging aperture, two regions matching it are searched in the binarized image, and the centroid coordinates (x1, y1) and (x2, y2) of the intensity values ​​in the corresponding regions are calculated as the basis for establishing the pixel coordinate transformation relationship of the interference field map.

[0116] Considering that the camera target surface is usually small, the difference between the coordinates of the two interferometric field images mainly lies in the horizontal and vertical displacement of the pixel coordinates. That is, the correspondence between the pixel coordinates of the two interferometric field sequences within a single frame of the camera image is expressed as follows:

[0117] I2(m,n)=I1(u+Δx,v+Δy)

[0118] Δx = x² - x₁, Δy = y² - y₁

[0119] When collecting actual object light intensity maps, the camera exposure value is adjusted to a higher level to enhance the contrast of the aperture edge and improve matching accuracy.

[0120] S5. Phase solution based on two-frame phase-shifted interferometric fringe patterns

[0121] This invention presents a phase solution process based on two-frame phase-shifted interferometric fringe patterns, using pixel registration results from the interferometric fringe patterns. This mainly includes phase demodulation based on the two-frame phase-shifted interferometric fringe patterns and noise-robust spatial phase unwrapping steps. Numerous research results have been achieved on these two aspects, therefore, a variety of specific algorithms can be used, and this invention is not limited to any particular method.

[0122] The measurement example employs a two-frame phase-shifting interferometric phase demodulation method based on elliptic fitting and least-squares iteration. This method has the advantage of handling potential intra- and inter-frame inconsistencies in the background and modulation terms of the interferometric field sequence, reducing the impact of ill-conditioned problem solving on the calculation results, and thus providing high-precision phase demodulation results. Phase unwrapping utilizes a phase expansion method based on Zernike polynomial fitting, which can provide high-quality, high-precision expanded phase even under high noise conditions.

[0123] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0124] To demonstrate the high-precision dynamic phase measurement capability of the method of the present invention, based on Figure 1 The measurement system shown performed phase measurements on a transparent phase-type object with XJTU engraved on its surface and on the mechanical deformation of a rough aluminum disk surface subjected to force.

[0125] Figure 5 The image shows the two-step phase-shifting interference fringe pattern and phase imaging results of the XJTU transparent object. Figure 6 The diagram shows the two-step phase-shift interference fringe pattern, the phase-shift deformation fringe pattern, and the deformation phase measurement results before and after the aluminum disk deformation. Regardless of the type of object being measured, the method of this invention can obtain the phase information of the object in its current state under a single exposure, meeting the requirements of dynamic measurement.

[0126] This verifies the feasibility and practicality of applying the method of the present invention to the field of dynamic high-precision measurement.

[0127] In summary, this invention provides a dynamic phase-shift interferometry system and method. By utilizing the synchronous polarization-phase modulation capability of a liquid crystal circular polarization grating on incident linearly polarized light, two interference fields with a 90° phase shift are generated. These interference fields are independent of each other, enabling single-frame synchronous recording of a phase-shift interferogram sequence. This simplifies the interferometric system structure, eliminating the need for optical field alignment between grating, polarization array, and camera dimensions, thus improving the applicability of the measurement method in various applications. Simultaneously, it avoids the influence of environmental interference on the phase shift, ensuring the accuracy of phase shift demodulation calculation and achieving high-precision interferometry. The entire system and method are characterized by their simple and compact structure, enabling high-precision quantitative phase imaging of optical surfaces and full-field, high-precision dynamic deformation measurement of rough surface objects, meeting the real-time and accuracy requirements of various precision measurement applications.

[0128] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A dynamic phase-shift interferometry method, characterized in that, Includes the following steps: S1. The first depolarizing beam splitter splits the beam into an object beam and a reference beam while maintaining the polarization state of the beam unchanged. After being reflected, the object beam and the reference beam are combined by the first depolarizing beam splitter and then simultaneously incident perpendicularly on a polarizing grating. The second and third polarizers adjust the polarization directions of the reference beam and the object beam to 45° and 0°, respectively. For the 45° linearly polarized reference beam, the light field distribution formed after modulation by the polarizing grating... for: in, , The complex amplitude of the reference beam with 45° polarization is used. As the initial complex amplitude of the reference light, For grating phase; The complex amplitude distribution of the optical field after the object light with 0° linear polarization passes through a polarization grating for: in, The initial complex amplitude of the object light; The left-hand and right-hand polarization components of the reference light and object light interfere with each other, forming two interference field intensity distributions. and They are respectively: in, The amplitude of the object light. As a reference light amplitude, The phase of the object light, The phase of the reference light; S2. When the incident light is linearly polarized, the outgoing light on the other side of the polarization grating has an energy ratio of 1:

1. Left-handed and right-handed circularly polarized light; when the incident light is circularly polarized, the outgoing light on the other side of the polarization grating contains only a single beam with the opposite rotation direction to the incident light. S3. Based on the simultaneous generation of two phase-shifted interference fields in step S2, control the relative distance between the interference fields and simultaneously record two phase-shifted interference fringe patterns on the same camera target surface. S4. When the object under test is an optical surface, the pixels of the two phase-shifting interferometric fringe patterns obtained in step S3 are registered, and the phase is solved based on the two phase-shifting interferometric fringe patterns to complete the dynamic phase-shifting interferometry measurement; specifically: Block the reference light and only collect the object light intensity distribution. and The intensity map is binarized; then, based on the shape of the imaging aperture, two regions matching it are searched in the binarized image, and the centroid coordinates of the intensity values ​​in the corresponding regions are calculated. and This serves as the basis for establishing the pixel coordinate transformation relationship of the interferometric field pattern; the phase is solved based on the two-frame phase-shifted interferometric fringe patterns; the correspondence between pixel coordinates between two interferometric field sequences within a single frame of a camera image is expressed as follows: in, , correspond and pixel coordinates, This represents the coordinate difference. S5. When the object being measured has a rough surface, perform high-precision dynamic phase measurement on the deformation of the rough surface.

2. The dynamic phase-shift interferometry measurement method according to claim 1, characterized in that, In step S3, the second mirror is used as the projection surface of the grating. The light emitted from the polarization grating is reflected by the second mirror and then passes through the polarization grating again. At this time, the spacing of the emitted light is... And it is reflected to the target surface of the camera through the second depolarizing beam splitter. The distance between the outgoing light and the mirror before reflection.

3. The dynamic phase-shift interferometry measurement method according to claim 2, characterized in that, Outgoing beam spacing for: in, s This indicates the distance between the grating and the projection surface; This indicates the angle of deflection of the emitted light.

4. The dynamic phase-shift interferometry measurement method according to claim 1, characterized in that, Step S5 is as follows: Pixel alignment was performed on the phase-shifted interferometry sequences of the object before and after deformation to obtain a three-step phase-shifted fringe pattern containing the surface deformation phase. Multi-frame phase-shift demodulation was then used to obtain the deformation phase information. The actual deformation amount is obtained by converting the phase diagram of the package. .

5. A dynamic phase-shift interferometry measurement system, characterized in that, The dynamic phase-shift interferometry measurement method according to any one of claims 1 to 4 includes a first depolarization beam splitter (6). On one side of the first depolarization beam splitter (6), a first polarizer (5), a collimating lens (4), a pinhole filter (3), a first attenuator (2), and a laser (1) are arranged in sequence at intervals. On the other side, a third polarizer (10) and an object (11) are arranged in sequence at intervals. On the upper side of the first depolarization beam splitter (6), a second polarizer (7), a second attenuator (8), and a first reflector (9) are arranged in sequence at intervals. On the lower side of the first depolarization beam splitter (6), an imaging lens (12), a second depolarization beam splitter (14), a polarization grating (15), and a second reflector (16) are arranged in sequence at intervals. On one side of the second depolarization beam splitter (14), a camera (13) is arranged. The polarization grating (15) is a liquid crystal circular polarization grating. The fast axis orientation of the liquid crystal molecules changes periodically and continuously along the x-direction, and the whole has a phase delay of λ / 2.

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