Transverse shear interference wavefront detection system and method based on cross-polarization birefringent crystal

Abstract

The invention belongs to the technical field of optical detection, and particularly relates to the field of optical wavefront detection, in particular to a lateral shear interference wavefront detection system and method based on an orthogonal polarization birefringent crystal. The system comprises a laser light source, wherein a polarizer and a beam splitter prism are sequentially arranged on an emergent light path of the laser light source; the invention discloses a polarization birefringent crystal, a reflector and a polarization camera. The method comprises the following steps: processing four phase shift interferograms, and extracting a wavefront gradient by using an arc tangent function; solving the system of linear equations to determine wavefront phase distribution by adopting an integral algorithm based on a least square method; and based on the extracted wavefront gradient, performing quantitative phase imaging by using a phase recovery algorithm. The device is simple in structure, high in stability and high in light energy utilization rate; the method is good in real-time performance, high in precision, capable of effectively restraining noise influences, capable of improving the precision of wavefront measurement, capable of meeting the requirement for high-precision optical system detection and wide in application range.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical detection, specifically relates to the field of optical wavefront detection, and particularly relates to a lateral shearing interference wavefront detection system and method based on an orthogonal polarization birefringent crystal. Background Art

[0002] In the field of optical measurement, wavefront measurement is crucial for evaluating the performance of optical systems, detecting the quality of optical components, etc.

[0003] Existing wavefront detection devices, such as traditional interferometers, Shack-Hartmann sensors, and traditional wavefront measurement methods, such as phase-shifting interferometry, confocal microscopy, all have many defects. These traditional technologies rely on reference optical paths or mechanical scanning, resulting in poor anti-interference ability. The reference optical path is easily affected by environmental vibrations and temperature drifts, and additional vibration isolation devices are required; the measurement speed is limited, and mechanical scanning or phase modulation makes the measurement time long, and dynamic real-time detection cannot be achieved; moreover, the system is complex, the optical paths of multiple components are bulky, and it is difficult to integrate into portable devices or industrial production lines.

[0004] Lateral shearing interferometry (LSI), as an emerging wavefront measurement technology, is based on the interference principle, does not require a reference optical path, effectively avoids the problem of environmental interference, and has strong anti-interference ability; it does not require mechanical scanning, can achieve rapid measurement, and meets the requirements of dynamic real-time detection; its system structure is relatively simple and is more easily integrated into portable devices or industrial production lines, providing a more advantageous solution for wavefront measurement.

[0005] Among them, the lateral shearing interference measurement technology based on polarization gratings has been widely applied in fields such as wavefront / surface topography measurement, quantitative phase imaging, etc. However, in some special application scenarios, the performance of the existing polarization gratings in the lateral shearing interference measurement technology based on polarization gratings cannot meet the requirements.

[0006] "A method for wavefront reconstruction of multi-directional four-wave shear interference" disclosed in the document with the patent number "ZL202210976307.X". The interferometer used includes a laser light source, an expanding and collimating system, a beam splitting element, a compensating element, a testing element, a reflecting mirror, a polarizer, an orthogonal shear beam splitting assembly, an analyzer, an imaging lens, and a CCD camera. The orthogonal shear beam splitting assembly includes a first birefringent crystal and a second birefringent crystal arranged on the light path of the light emitted from the polarizer. Among them, the direction of the transmission axis of the polarizer forms an angle of 0° with the x-axis, the optical axis of the first birefringent crystal forms an angle of 45° with the x-axis, the second birefringent crystal rotates 45° vertically relative to the first birefringent crystal, and the direction of the transmission axis of the analyzer forms an angle of 45° or 135° with the x-axis. Through a precision automatic rotation platform, N orthogonally sheared four-wave interference images in multiple directions are collected on the CCD camera. The Fourier transform method is used to extract N groups of differential phases of four-wave shear interference in N different orthogonal directions respectively. Then, the differential Zernike polynomial fitting method and the least square method are used to solve and obtain multiple groups of basis function coefficients. The post-processing fusion method is used to solve the multi-dimensional data to obtain the best surface shape fitting coefficients, thereby reconstructing a complete surface shape with high precision. The problems it has are as follows: 1. Due to the orthogonality depending on the algorithm complexity, this method needs to rely on shear interference images in multiple orthogonal directions during the wavefront reconstruction process, and its reconstruction accuracy will be directly affected by the orthogonality of the shear interference images. Although the dimensionality loss is compensated by multi-directional data acquisition, it increases the complexity of solving the basis function coefficients and will affect the real-time performance. 2. This scheme has limitations in dealing with boundary errors. The method for dealing with the problem of discontinuous boundaries of the interference images is not clearly mentioned in the scheme. At the same time, there are error sources caused by device limitations in this scheme. Although it aims to reduce the dependence on two-dimensional diffraction devices, a precision rotation platform is still required in the implementation process to obtain multi-directional interference images. If the rotation accuracy of the platform is insufficient, it may lead to calibration errors in the shear direction, thereby affecting the extraction accuracy of the differential phase.

[0007] "A compensation method in the wavefront reconstruction process of grating lateral shearing interference" disclosed in the document with the patent number "ZL202110720859X" proposes a dynamic compensation algorithm to address the problems of pupil distortion and shear amount variation in grating shearing interference, reducing the impact of device errors on phase extraction. This patent presents effective solutions for grating defocus compensation and coordinate distortion correction, but it is still limited by computational complexity, noise sensitivity, and high-order aberration compensation capabilities. It is necessary to combine anti-noise algorithm optimization and hardware acceleration design to improve practicality. The problems it has are as follows: 1. The dynamic compensation has a high computational complexity. The optical path tracing and coordinate system transformation require real-time calculation of the propagation paths of diffracted wavefronts at all orders, resulting in a significant increase in algorithm complexity. Especially in dynamic measurement scenarios (such as thermal deformation monitoring of optical components), real-time performance may be limited by hardware computing power and it is difficult to meet the high-frame-rate detection requirements. 2. There is a problem of relying on the accuracy of optical path tracing. The compensation effect highly depends on the accuracy of the optical path tracing model. If the grating etching error or alignment deviation causes the diffraction angle to deviate from the theoretical value, the coordinate transformation relationship will produce errors, ultimately affecting the reliability of shear amount correction. 3. Frequent calibration of grating parameters is required in the experimental environment, increasing the operation complexity. 4. The applicable scenarios are limited. This method is designed for grating shearing interference. If applied to other shearing devices (such as prisms or beam splitters), the optical path tracing process needs to be re-modeled, and the algorithm has low generality. In addition, the defocus amount range needs to be preset during the compensation process, and it has weak adaptability to sudden defocus (such as vibration shock). 5. In extreme environments such as high temperature and strong radiation, the stability of the polarization grating is poor, resulting in affected measurement results, thus causing large errors in the performance of the evaluated optical system and the quality of the detected optical components.

[0008] "A method for improving the detection sensitivity of a four-wave lateral shearing interferometer in general" disclosed in the document with the patent number "ZL202210987611.4" needs to separate four-wave interference fringes through Fourier transform, but it is necessary to adjust the distance between the grating and the camera multiple times to improve sensitivity, resulting in complex operation and error accumulation.

[0009] Therefore, it is of great significance to develop a new, stable and reliable lateral shearing interference wavefront measurement technology. Summary of the Invention

[0010] The present invention provides a lateral shearing interference wavefront measurement method and device based on an orthogonally polarized birefringent crystal to overcome the problems existing in the prior art that it is necessary to adjust the distance between the grating and the camera multiple times to improve sensitivity, resulting in complex operation and error accumulation.

[0011] To achieve the above object, the technical solution of the present invention is: A lateral shearing interference wavefront measurement system based on an orthogonally polarized birefringent crystal, comprising a laser light source, a polarizer, a beam splitter prism, a polarization birefringent crystal, a reflector, and a polarization camera sequentially arranged on the light path emitted by the laser light source.

[0012] Furthermore, the above-mentioned polarization birefringent crystal is a lithium niobate crystal or a quartz crystal.

[0013] Furthermore, the measurement method of the above-mentioned transverse shear interference wavefront measurement device based on an orthogonal polarization birefringent crystal includes the following steps:

[0014] Step 1: By processing four phase-shifted interference patterns, the wavefront gradient ΔW can be extracted using the arctangent function. x

[0015]

[0016] At the polarization camera (6), the light wave passes through polarizers at different angles to obtain the light intensity expressions of four phase-shifted interference patterns.

[0017] I α (α = 0, π / 4, π / 2, 3π / 4) (2)

[0018] I α = |E1 + E2| 2 = 2 + 2cos (3)

[0019] where k is the wave number, ΔW x is the wavefront gradient in the x direction, and E1 and E2 are the Jones matrices of the two shear light beams respectively;

[0020] Step 2: Adopt an integral algorithm based on the least squares method to determine the phase distribution of the wavefront by solving a system of linear equations;

[0021] Step 3: Based on the extracted wavefront gradient ΔW x , perform quantitative phase imaging using a phase retrieval algorithm.

[0022] Furthermore, the specific steps of the above Step 3 are as follows:

[0023] Step 3.1, Acquisition and preprocessing of interferogram data;

[0024] Step 3.2, Wavefront gradient field calculation;

[0025] Step 3.3, Perform wavefront reconstruction and measurement verification;

[0026] Step 3.4, Use an iterative algorithm to perform quantitative phase imaging.

[0027] Furthermore, in the above Step 3.2, when calculating the wavefront gradient field, the phase difference solution uses the four-step phase-shift formula to extract the wrapped phase.

[0028]

[0029] Among them, I0 to I3 are the intensity distributions of four-step phase-shifting interference patterns.

[0030] Furthermore, the specific steps of the above step 3.3 are as follows:

[0031] According to the refractive index or topography mapping, convert the restored absolute phase value into a physical quantity

[0032]

[0033] Where λ is the wavelength of the light source.

[0034] Furthermore, in the above step 3.4, the iterative algorithm adopted is to alternately iterate between the spatial domain and the frequency domain to continuously optimize the phase distribution. In each iteration, update the phase information according to the measured interference pattern, and correct the phase using the constraint conditions of the wavefront to obtain a high-precision quantitative phase image.

[0035] Furthermore, in the above step 3.4, the ΔW measured by lateral shearing interferometry x represents the height difference between the original surface column vectors (X k ) and the lateral shear amount of s in the x direction. The matrix representation is

[0036] ΔW x =[(X s+1 -X1)…(X 2s+1 -X s+1 )…(X 3s+1 -X 2s+1 )…] (6)

[0037] When only the results of the surface gradient vectors (X k+s -X k ) at each s interval are selected and accumulated, the wavefront gradient topography is obtained. The topography (W s ) at the s interval is partially restored as:

[0038] W s =[(X s+1 -X1)(X 2s+1 -X1)(X 3s+1 -X1)…] (7)

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. The device has a simple structure, high stability, and high light energy utilization rate:

[0041] (1) The present invention directly generates four-wave shear beams through a single orthogonally polarized birefringent crystal, eliminating the need for multi-stage beam splitting prisms and polarization gratings, simplifying the optical path structure, and reducing the number of components by more than 40%.

[0042] (2) Compared with the polarization grating, the polarization birefringent crystal provided by the present invention forms a polarization-orthogonal four-wave transverse shear interference model through a single polarization birefringent crystal, realizing polarization-state orthogonal four-wave transverse shear interference. It has a simple structure and no diffracted light, and has better stability in extreme environments such as high temperature and strong radiation, which can ensure the reliable operation of the measurement device under harsh conditions and expand the application range of wavefront measurement technology.

[0043] (3) The present invention uses a polarization birefringent crystal to directly suppress stray light through the polarization-orthogonal characteristics of the crystal, improving the utilization rate of light energy. This is because the polarization birefringent crystal adopted by the present invention decomposes the incident light into o-light and e-light with orthogonal vibration directions based on the anisotropic characteristics of the crystal, and realizes polarization modulation through phase delay and polarization-state separation. The present invention adopts a single-crystal structure with high optical path integration. The common optical path design reduces environmental interference, and the polarization stability error is <0.5% in a wide temperature range (-40°C to 80°C); the transmittance of the birefringent crystal is >90%, and there is no diffraction and direct light splitting, while the transmittance of the polarization grating is usually 70% - 85% due to absorption and scattering losses. The polarization birefringent crystal is significantly superior to the polarization grating in terms of polarization purity, stability, and anti-damage performance.

[0044] 2. The device of the present invention has high sensitivity, good real-time performance, and high precision:

[0045] The present invention utilizes the crystal birefringence phase delay characteristic to directly extract the phase in the orthogonal shear direction from a single-frame interference pattern without mechanical adjustment, improving the sensitivity: by analyzing the phase difference of the orthogonal polarization states through an algorithm, the sensitivity of wavefront slope detection is improved; the processing speed of a single frame is increased, enhancing the real-time performance, and it is applicable to dynamic wavefront monitoring.

[0046] 3. The present invention effectively suppresses the influence of noise and improves the accuracy of wavefront measurement through an optimized numerical integration wavefront reconstruction method and a quantitative phase imaging method, which can meet the requirements of high-precision optical system detection. The specific analysis is as follows:

[0047] (1) Good anti-noise performance and error control:

[0048] The numerical integration method adopted in step one can effectively reduce the influence of noise on the reconstruction result by optimizing the selection of the integration path. Compared with the least-square statistical solution of the region method, this method can reduce the cumulative error caused by random noise through the optimized design of the direct integration path.

[0049] (2) Strong applicability to complex scenarios:

[0050] Compared with the Fried / Southwell model that relies on a specific geometric model, the numerical integration method adopted in Step 1 can adapt to different sensor layouts and complex wavefront morphologies by adaptively adjusting the integration kernel function. For example, in microscopic holography, this method can still maintain a high reconstruction accuracy when the Fresnel approximation condition is not satisfied.

[0051] (3) Fast calculation efficiency:

[0052] In Step 1, the wide-window method and the frequency-domain band-limited method numerical optimization strategies are adopted, which significantly improve the operation speed while maintaining the accuracy. During the wavefront reconstruction and phase retrieval processes, the combination of the wide-window method and the frequency-domain band-limited method can significantly improve the calculation efficiency while maintaining the numerical accuracy, enabling high-precision wavefront reconstruction with single exposure in ultrafast optical measurements.

[0053] (4) Strong data fusion ability.

[0054] 4. The method of the present invention has a wide range of applications: By using a polarization birefringent crystal to replace the polarization grating and improving the lateral shear interference measurement technology, it can work stably under more extensive environmental conditions, providing a more reliable technical means for optical wavefront detection. The measurement method and device of the present invention are applicable to the high-precision dynamic measurement of the surface topography of optical elements and the wavefront phase distribution, especially for realizing fast and stable quantitative phase imaging in industrial sites and complex environments. Therefore, it can be widely applied to multiple fields such as optical element manufacturing, astronomical observation, and biomedical imaging, providing strong support for the optimization and performance evaluation of optical systems. Description of the Drawings

[0055] Figure 1 : Schematic diagram of the device structure;

[0056] Figure 2 : Schematic diagram of the structure of the polarization birefringent crystal and the principle of polarization beam splitting;

[0057] Figure 3 : Four-phase interference pattern and flowchart for wavefront gradient calculation, where s is the shear distance in the figure;

[0058] Figure 4 : Local distortion of the surface topography of the optical element captured by the wavefront reconstruction algorithm of the present invention

[0059] Among them: (a) Standard wavefront residual map; (b) Measured wavefront residual map drawn.

[0060] The reference numerals are as follows:

[0061] 1 - Laser light source, 2 - Polarizer, 3 - Beam splitter prism, 4 - Polarization birefringent crystal, 5 - Reflecting mirror,

[0062] 6 - Polarization camera. Detailed Embodiments

[0063] The following will be described in detail with reference to the accompanying drawings and embodiments.

[0064] See Figure 1 , a lateral shear interference wavefront measurement system based on an orthogonally polarized birefringent crystal, comprising a laser light source 1, a polarizer 2, and a beam splitter prism 3 sequentially arranged on the light path of the light emitted by the laser light source; a polarization birefringent crystal 4, a mirror 5, and a polarization camera 6. The polarization birefringent crystal 4 is a lithium niobate crystal or a quartz crystal.

[0065] The incident test light wave forms a linearly polarized light wave through the polarizer 2, and then is emitted to the birefringent crystal 4 through the beam splitter prism 3. After the incident light wave passes through the birefringent crystal 4 and undergoes beam separation, it is incident on the mirror 5. A part of the light wave separated from the birefringent crystal 4 is reflected to the mirror 5 and then reflected back to the birefringent crystal 4. The reflected light wave enters the birefringent crystal 4, and the birefringent crystal 4 performs birefringence processing on the light wave. The light wave processed by the birefringent crystal 4 is then separated into different paths by the beam splitter prism 3 and finally enters the polarization camera 6 for imaging and analysis. A polarization filter array is arranged in the polarization camera 6. The polarization filter array includes 4 polarization filters, and the angles of each polarization filter are 0°, 45°, 90°, and 135° respectively. These polarization filters are used to analyze the polarization state of the light wave.

[0066] The light emitted by the laser light source 1 is changed into linearly polarized light by the polarizer 2. In this embodiment, the central wavelength of the laser light source 1 is [λ = 633 nm], and the polarization direction matches the optical axis direction of the subsequent polarization birefringent crystal 4. The linearly polarized light is incident on the polarization birefringent crystal 4. The polarization birefringent crystal 4 has birefringence characteristics and can cause phase delay and polarization state change when the incident linearly polarized light propagates along the optical axes in different directions. In the crystal, the propagation speeds of the o-ray (ordinary ray) and the e-ray (extraordinary ray) are different, resulting in a phase difference. After being reflected by the mirror 5, it passes through the polarization birefringent crystal 4 again to achieve lateral shear of the light. The mirror 5 and the polarization birefringent crystal 4 are closely cooperated to ensure the stability of the light path when the light passes through the crystal twice. Finally, the sheared light enters the polarization camera 6. Pixelized polarizers with 0°, 45°, 90°, and 135° rotating transmission axes are provided in front of the pixels of the polarization camera 6, and four-phase-shifted lateral shear interference patterns can be obtained simultaneously.

[0067] A measurement method for a lateral shear interference wavefront measurement device based on an orthogonally polarized birefringent crystal provided by the present invention includes the following steps: [[ID=!7]]

[0068] Step 1: By processing the four-phase-shifted interference patterns, the wavefront gradient ΔW can be extracted using the arctangent function x

[0069]

[0070] See Figure 2 Figure 2 , when linearly polarized light is incident on the polarization birefringent crystal 4, according to the birefringence principle, the light is decomposed into the o-ray and the e-ray, and their propagation directions and polarization states are different. After being reflected by the mirror and passing through the crystal again, the propagation paths of the o-ray and the e-ray undergo a lateral shift, forming lateral shear interference. Let the Jones matrix of the incident light be E in Figure 2 , after the action of the polarization birefringent crystal and the mirror, the Jones matrices of the two shear lights are E1 and E2 respectively.

[0071] See Figure 3 Figure 3 , at the polarization camera, the light wave passes through polarizers at different angles, and according to the operation rules of the Jones matrix, the light intensity expressions of the four phase-shifted interference patterns are obtained

[0072] I α (α = 0, π / 4, π / 2, 3π / 4) (2)

[0073] I α = |E1 + E2| 2 = 2 + 2cos (3)

[0074] where k is the wave number, and ΔW x is the wavefront gradient in the x direction.

[0075] Step 2: Adopt the integral algorithm based on the least squares method to determine the phase distribution of the wavefront by solving a system of linear equations. This algorithm can effectively suppress the influence of noise on wavefront reconstruction and improve the reconstruction accuracy. At the same time, combined with the known measurement surface information and boundary conditions, the integral process is constrained to ensure the accuracy of the reconstructed wavefront.

[0076] Step 3: Based on the extracted wavefront gradient ΔW x , use the phase retrieval algorithm for quantitative phase imaging:

[0077] In this step, the phase retrieval algorithm is adopted: model the mathematical relationship between the wavefront gradient ΔW x and the phase distribution W(x, y). Since ΔW x reflects the spatial change rate of the phase, reconstruct the continuous phase distribution through the iterative integral method, construct an objective function (such as the gradient matching error) and iteratively optimize the phase distribution, adopt the improved Gerchberg-Saxton (GS) algorithm to process the wavefront gradient, reconstruct the wavefront and perform quantitative phase imaging to obtain the phase distribution data of the wavefront, and then realize wavefront measurement. The specific steps are as follows:

[0078] Step 3.1, Acquisition and preprocessing of interference pattern data:

[0079] The interference pattern data acquisition uses a polarization camera to synchronously record four sets of phase-shifted interference patterns generated by a birefringent crystal (phase differences are 0, π / 2, π, and 3π / 2 respectively). The test wave and the reference wave are separated by a beam splitter prism, and the optical path alignment is optimized by combining mirrors.

[0080] The preprocessing performs Gaussian filtering on the original interference pattern to eliminate speckle noise, removes phase jitter caused by environmental vibration through spatial averaging, and simultaneously deducts the background interference field without the sample to complete noise suppression and background correction.

[0081] Step 3.2, Wavefront gradient field calculation:

[0082] Phase difference calculation uses the four-step phase-shift formula to extract the wrapped phase:

[0083]

[0084] where I0 to I3 are the intensity distributions of the four-step phase-shifted interference patterns.

[0085] During the phase unwrapping process, the least squares method or the quality-guided path tracking algorithm is used to eliminate the 2π jumps in the wrapped phase and restore the continuous phase distribution.

[0086] Step 3.3, Perform wavefront reconstruction and measurement verification:

[0087] According to the refractive index or topography mapping, the restored absolute phase value is converted into a physical quantity (such as the sample thickness h or the refractive index change Δn):

[0088]

[0089] where λ is the wavelength of the light source.

[0090] During error evaluation and calibration, the measurement accuracy is verified by using a known standard sample (such as a step height calibration chip), and the system aberration is corrected by Zernike polynomial fitting. Finally, a quantitative phase image with sub-nanometer resolution is output.

[0091] Step 3.4, Use an iterative algorithm for quantitative phase imaging:

[0092] In this embodiment, an improved version of the Gerchberg-Saxton algorithm is used. This algorithm alternately iterates between the spatial domain and the frequency domain, continuously optimizing the phase distribution to make the reconstructed phase more matched with the measured interference pattern data. In each iteration, the phase information is updated according to the measured interference pattern, and the phase is corrected using the constraints of the wavefront (such as the continuity and smoothness of the wavefront), so as to obtain a high-precision quantitative phase image that accurately reflects the phase distribution of the wavefront.

[0093] Based on the surface height, that is, using the basic principle of wavefront partial reconstruction, the phase height difference is represented by the difference between the surface heights of two lateral shear interferograms. The ΔW measured by lateral shear interferometry x represents the height difference between the original surface column vectors (X k ), and the lateral shear amount of s in the x direction can be represented by a matrix.

[0094] ΔW x = [(X s+1 - X1)…(X 2s+1 - X s+1 )…(X 3s+1 - X 2s+1 )…] (6)

[0095] When only the results of the surface gradient vectors (X k+s - X k ) at each s interval are selected and accumulated, the wavefront gradient surface shape is obtained. The surface shape (W s ) at the s interval can be partially restored as:

[0096] W s = [(X s+1 - X1)(X 2s+1 - X1)(X 3s+1 - X1)…] (7)

[0097] Using the method of the present invention for testing, the specific steps are as follows: The polarization camera simultaneously collects four phase-shifted interferograms and transmits the data to the computer; in the computer, the wavefront gradient is calculated according to the formula in the above measurement principle. An integration algorithm based on the least squares method and an improved Gerchberg-Saxton algorithm are used to process the wavefront gradient, reconstruct the wavefront and perform quantitative phase imaging to obtain the phase distribution data of the wavefront.

[0098] Analyze the reconstructed wavefront data to evaluate the performance of the optical system or detect the quality of the optical element. By comparing with the standard wavefront data, calculate the wavefront error, such as the peak-to-valley value (PV), root mean square value (RMS), etc., to determine whether the optical element meets the design requirements. By comparing the reconstructed wavefront data with the standard wavefront (ideal wavefront or design wavefront), the aberration of the optical system can be quantified. The core error indicators include: the peak-to-valley value (PV) reflecting the maximum fluctuation range of the wavefront error, PV = max(W 实测 - W 标准 ) - min(W 实测 - W 标准 ), and the root mean square (RMS) used to characterize the statistical distribution of the wavefront error. By using the Zernike polynomial decomposition again, the wavefront error is decomposed into Zernike coefficients to identify the aberration type. By plotting the residual map of the measured wavefront and the standard wavefront, the spatial distribution of the error can be visually displayed, such as Figure 4 shown. By comparing the standard wavefront residual map and the plotted measured wavefront residual map, it can be found that the wavefront reconstruction algorithm of the present invention can accurately capture the local distortion of the surface topography of the optical element, and its error distribution is highly consistent with the design expectation (the RMS error is reduced to λ / 15), verifying its high-precision advantage in micro-nano optical detection.

[0099] The above description is an illustration of the specific implementation of the present invention, rather than a limitation thereof. Those skilled in the relevant technical field can also make various equivalent technical solutions without departing from the scope of the present invention. Therefore, all equivalent technical solutions should be included in the protection scope of the present invention.

Claims

1. A lateral shear interference wavefront measurement system based on an orthogonally polarized birefringent crystal, comprising a laser light source (1), characterized in that: A polarizer (2), a beam splitting prism (3), a polarization birefringent crystal (4), a reflector (5) and a polarization camera (6) are sequentially arranged on the light path of the laser light source (1).

2. The transverse shear interference wavefront measurement system based on an orthogonally polarized birefringent crystal according to claim 1, wherein: The polarization birefringent crystal (4) is a lithium niobate crystal or a quartz crystal.

3. The measuring method of the transverse shearing interference wavefront measuring device based on an orthogonally polarized birefringent crystal according to claim 1, characterized in that: It includes the following steps: Step 1: By processing four phase-shifted interferograms, the wavefront gradient ΔW can be extracted using the arctangent function x At the polarization camera (6), the light wave passes through polarizers at different angles to obtain the light intensity expressions of four phase-shifted interference patterns I α (α＝0,π / 4,π / 2,3π / 4) (2) I α = |E1 + E2| 2 = 2 + 2cos(3) where k is the wave number, ΔW x is the wavefront gradient in the x direction, and E1 and E2 are the Jones matrices of the two shearing beams respectively; Step 2: Adopt an integral algorithm based on the least square method to determine the phase distribution of the wavefront by solving a system of linear equations. Step 3: Based on the extracted wavefront gradient ΔW x , perform quantitative phase imaging using a phase retrieval algorithm.

4. The measuring method of the transverse shear interference wavefront measuring device based on an orthogonally polarized birefringent crystal according to claim 3, characterized in that: The specific steps of Step 3 are as follows: Step 3.1: Acquisition and preprocessing of interference pattern data; Step 3.2: Calculation of wavefront gradient field; Step 3.3: Conduct wavefront reconstruction and measurement verification; Step 3.4: Adopt an iterative algorithm for quantitative phase imaging.

5. The measuring method of the transverse shear interference wavefront measuring device based on an orthogonally polarized birefringent crystal according to claim 4, characterized in that: In Step 3.2, when calculating the wavefront gradient field, the phase difference solution extracts the wrapped phase by using the four-step phase shift formula where I0 to I3 are the intensity distributions of the four-step phase-shifted interference patterns.

6. The measuring method of the transverse shear interference wavefront measuring device based on an orthogonally polarized birefringent crystal according to claim 5, characterized in that: The specific steps of Step 3.3 are: Convert the recovered absolute phase value into a physical quantity according to the refractive index or topography mapping where λ is the wavelength of the light source.

7. The measuring method of the transverse shearing interference wavefront measuring device based on an orthogonal polarization birefringent crystal according to claim 4, characterized in that: In Step 3.4, the iterative algorithm adopted alternately iterates between the spatial domain and the frequency domain to continuously optimize the phase distribution. In each iteration, the phase information is updated according to the measured interference pattern, and the phase is corrected by using the constraint conditions of the wavefront to obtain a high-precision quantitative phase image.

8. The measuring method of the transverse shearing interference wavefront measuring device based on an orthogonally polarized birefringent crystal according to claim 4, characterized in that: In the said step 3.4, ΔW measured by lateral shear interferometry x represents the height difference between the original surface column vectors (X k ), and the lateral shear of s in the x direction. The matrix representation is ΔW x = [(X s+1 - X1)…(X 2s+1 - X s+1 )…(X 3s+1 - X 2s+1 )…] (6) When only the results of the surface gradient vectors (X k+s -X k ) at each s interval are selected and accumulated, the wavefront gradient surface shape is obtained, and the surface shape (W s ) at the s interval is partially restored as: W s = [(X s+1 - X1)(X 2s+1 - X1)(X 3s+1 - X1)…] (7).

Images