A four-wave phase-shift point-diffraction interferometer for wavefront probing

Abstract

This application relates to the field of wavefront detection technology, specifically to a four-wave phase-shifting point diffraction interferometer for wavefront detection, aiming to solve the problems of limited performance and susceptibility to environmental interference in dynamic scenarios of traditional point diffraction interferometers. The point diffraction interferometer includes: a beam splitting module, a test arm modulation module, a reference arm modulation module, a beam combining interferometer module, and a detection and restoration module. The test arm modulation module is sequentially equipped with a first focusing lens, a plane mirror, a beam splitter grating, and a first collimating lens. The reference arm modulation module is sequentially equipped with a second focusing lens, a plane mirror, a filter, a second collimating lens, and a partitioned fixed phase modulation element. The beam combining interferometer module combines the beams from the test arm and the reference arm. The detection and restoration module includes a photodetector and a data processing unit for acquiring the wavefront phase of the incident distorted wavefront. This application's four-wave phase-shifting point diffraction interferometer for wavefront detection significantly improves the performance and stability of wavefront detection.

Description

Technical Field

[0001] This application relates to the field of wavefront detection technology, and in particular to a four-wave phase-shifting point diffractometer for wavefront detection. Background Technology

[0002] Wavefront detection technology is a core technology in the field of optics for characterizing the phase distribution of light beams. It is widely used in many key fields such as optical component testing, laser communication, and astronomical observation, and provides important support for the performance optimization, precise operation and technological breakthroughs of optical systems in various fields.

[0003] Among numerous wavefront detection technologies and equipment, the point diffraction interferometer, with its core measurement principle of using pinhole diffraction to generate an ideal spherical wave as a reference wave, has wide applications in the field of high-precision phase detection and is one of the core devices for current precision wavefront detection. Currently, Shak-Hartmann wavefront sensors are a commonly used type of equipment in the field of wavefront detection. However, compared with point diffraction interferometers, Shak-Hartmann wavefront sensors have three major technical defects, making it difficult to meet the application requirements of some high-precision and complex scenarios: First, this type of sensor relies on sub-aperture arrays to divide the incident beam. The size of the sub-apertures directly limits the phase sampling density, resulting in low spatial resolution and an inability to accurately capture subtle wavefront phase changes. Second, its wavefront phase calculation relies on the light intensity distribution within the sub-apertures to solve for the wavefront slope. If there is light intensity flicker, it will directly interfere with the accuracy of the slope calculation results, making it less resistant to light intensity flicker. Third, the phase information between sub-apertures needs to be integrated through interpolation and splicing. This process cannot accurately capture the abrupt changes in phase vortex characteristics, making it difficult to identify phase vortexes and resulting in poor applicability in wavefront detection scenarios where phase vortexes exist. The aforementioned shortcomings make it difficult for the Shaker-Hartmann wavefront sensor to meet the practical application requirements in scenarios with stringent requirements for wavefront detection accuracy, resolution, and anti-interference capabilities, such as precision optical component testing and astronomical observation in strong turbulent environments.

[0004] Although point diffraction interferometers have advantages in high-precision wavefront detection, traditional point diffraction interferometers still face unresolved technical bottlenecks that limit their application effectiveness and measurement accuracy in dynamic interference scenarios. Specifically, traditional point diffraction interferometers mostly employ time-domain phase-shifting techniques to achieve phase measurement. This technique requires changing the phase of the reference wave multiple times by mechanically shifting the reflector and adjusting the electro-optic modulator, acquiring multiple interferometric images accordingly, and then performing phase calculation based on these multiple interferometric images. This time-domain phase-shifting measurement method not only results in long single wavefront detection times and low measurement efficiency, but more importantly, in dynamic interference scenarios such as strong turbulence and external vibrations, the wavefront under test changes in real time due to dynamic interference during multiple acquisitions of interferometric images. This causes the interferometric images acquired at different times to not correspond to the same wavefront state, thus introducing phase measurement errors. In addition, the phase shifter used in this technology requires strict phase calibration before use, and the performance of the phase shifter is easily affected by changes in environmental factors such as temperature and humidity, further aggravating phase measurement errors and reducing the measurement stability and reliability of traditional point diffraction interferometers in complex scenarios. Summary of the Invention

[0005] To address the aforementioned technical problems in the prior art, namely the limited performance and susceptibility to environmental interference in dynamic scenarios of traditional point diffraction interferometers, embodiments of this application provide a four-wave phase-shifting point diffraction interferometer for wavefront detection, comprising:

[0006] Beam splitting module, test arm modulation module, reference arm modulation module, beam combining interference module, and detection and restoration module;

[0007] The beam splitting module includes a beam splitter for splitting the incident distorted wavefront into a test arm beam and a reference arm beam, wherein the test arm beam is the beam to be tested and the reference arm beam is the reference beam.

[0008] The test arm modulation module is sequentially provided with a first focusing lens, a plane mirror, a beam splitter, and a first collimating lens;

[0009] The reference arm modulation module is sequentially provided with a second focusing lens, a plane mirror, a filter, a second collimating lens, and a partitioned fixed phase modulation element;

[0010] The beam combining interference module includes a beam splitter, which is used to combine the beams output by the test arm modulation module and the reference arm modulation module to form four interference spots.

[0011] The detection and restoration module includes a photodetector and a data processing unit. The photodetector acquires images of the four interference spots, and the data processing unit obtains the wavefront phase of the incident distortion wavefront based on the images of the four interference spots through a winding phase extraction algorithm and a dewinding algorithm.

[0012] The optical axis of the four-wave phase-shifting point diffraction interferometer used for wavefront detection is determined by the line connecting the optical centers of the first focusing lens and the first collimating lens, and the line connecting the optical centers of the second focusing lens and the second collimating lens, and the optical centers of the first focusing lens, the first collimating lens, the second focusing lens, and the second collimating lens are all aligned with the optical axis of the system.

[0013] Optionally, the beam to be tested, located at the front focal plane of the first focusing lens, is focused by the first focusing lens and then incident on a beam splitter located at the rear focal plane of the first focusing lens. After modulation, four diffracted beams at different angles are generated. The diffracted beams are collimated by the first collimating lens and then transmitted to the beam combining interference module. The reference beam, located at the front focal plane of the second focusing lens, is focused by the second focusing lens and then incident on a filter located at the rear focal plane of the second focusing lens. After modulation, an ideal spherical reference wavefront is generated. The ideal spherical reference wavefront is collimated by the second collimating lens and then modulated by a partitioned fixed phase modulation element before being transmitted to the beam combining interference module.

[0014] Optionally, the rear focal plane of the first focusing lens completely overlaps with the front focal plane of the first collimating lens, the beam splitter is placed at the overlap of the rear focal plane of the first focusing lens and the front focal plane of the first collimating lens, and the optical centers of the first focusing lens and the first collimating lens are both aligned with the optical axis of the system.

[0015] Optionally, the rear focal plane of the second focusing lens completely coincides with the front focal plane of the second collimating lens, the filter is placed at the point where the rear focal plane of the second focusing lens coincides with the front focal plane of the second collimating lens, and the optical centers of the second focusing lens and the second collimating lens are aligned with the optical axis of the system.

[0016] Optional, the period length of the beam splitter grating With the first diffraction angle The relationship is: ,in For the operating wavelength, , The diameter of the incident pupil. The focal length of the first focusing lens. This refers to the size of the receiving surface of the photodetector. Let be the focal length of the first collimating lens. It is the diameter of the diffraction spot on the back focal plane of the first collimating lens.

[0017] Optionally, the beam splitter is a checkerboard phase grating, which is a binary phase modulation plate, and the phase shift function of the checkerboard phase grating is... , where the symbol Indicates rounding down. The grating period of the chessboard phase grating is given. The coordinates of the phase grating in the plane are Cartesian coordinates. For any integer, based on the phase shift function, the grating plane of the chessboard phase grating forms a chessboard-like phase distribution with alternating "0-π".

[0018] Optionally, the Fourier transform of the transmittance function of the chessboard phase grating is expressed as:

[0019] ,

[0020] in, The coordinates of the phase grating in the plane are Cartesian coordinates. Let be the transmittance function of the chessboard phase grating. They are respectively Diffraction order in direction, sign Represents the two-dimensional Fourier transform operator. Represents the two-dimensional Fourier transform operator. Represents the Dirac function, For corresponding Spatial frequency in the axial direction, For corresponding Spatial frequency in the axial direction.

[0021] Optional, , for Complex amplitude distribution at the rear focal plane of the first collimating lens ,in, The complex amplitude distribution of the incident distorted wavefront. for The complex amplitude distribution at the rear focal plane of the first focusing lens after passing through the first focusing lens. Let be the focal length of the first collimating lens. The focal length of the first focusing lens. For the operating wavelength, The coordinates are rectangular coordinates within the rear focal plane of the first focusing lens. The coordinates are rectangular coordinates within the rear focal plane of the first collimating lens. For function The two-dimensional Fourier transform result, Indicates an index. After being modulated by the checkerboard phase grating, it is transmitted to the back focal plane of the first collimating lens.

[0022] Optionally, the filter is a pinhole filter, wherein the pinhole diameter of the pinhole filter is... ,in For the operating wavelength, The focal length of the second focusing lens. The aperture of the pinhole filter is the entrance pupil diameter, and the center of the aperture is aligned with the focal point after imaging by the second focusing lens.

[0023] Optionally, the partitioned fixed phase modulation element is a four-part phase plate, which is divided into four quadrants according to a rectangular coordinate system. The phase differences of the four quadrants are 0, π / 2, π and 3π / 2 respectively. The partitioned fixed phase modulation element is located after the second collimating lens, and the optical axis of the system passes through the center of the partitioned fixed phase modulation element.

[0024] The beneficial effects of this application embodiment compared with the prior art are as follows: First, by introducing a beam splitting grating at the rear focal plane of the first focusing lens, the incident beam can be effectively split into four diffracted beams with different propagation angles. After being collimated by the first collimating lens, these four diffracted beams can be stably output as four small-aperture, crosstalk-free fine beams. By adjusting the focal length matching relationship between the first focusing lens and the first collimating lens, a suitable beam reduction ratio can be flexibly obtained, and the size of the output fine beam can be flexibly adjusted for different turbulence intensity scenarios, thereby adapting to diverse wavefront detection accuracy requirements and significantly improving the scene adaptability and application flexibility of the equipment. Second, by using a beam splitting grating based on the phase modulation principle to achieve beam splitting, compared with traditional beam splitting elements, this method does not have additional light absorption phenomena, has higher beam energy utilization, and can effectively ensure the light intensity stability of subsequent interferometric measurements; at the same time, based on the beam splitting characteristics of phase modulation, the grating is less affected by external environmental factors (such as temperature and humidity), has stronger environmental adaptability, and can work stably under complex working conditions. Finally, by setting a partitioned fixed phase modulation element after the second collimating lens, partitioned fixed phase modulation is applied to the reference wavefront, so that the reference beam and the four thin beams output by the test arm form spatial phase-shifted interference. This design can realize the simultaneous acquisition of four interferograms with different phase shifts in a single measurement. Compared with the traditional time-domain phase-shifting technology, it significantly shortens the time of a single wavefront detection and significantly improves the detection efficiency. At the same time, this spatial phase-shifting method does not require the setting of moving parts such as mechanical translation mirrors and electro-optic modulators, nor does it require complex phase calibration operations. It effectively avoids various problems in the time-domain phase-shifting technology, such as phase drift caused by wear of moving parts and environmental interference, as well as measurement deviations introduced by calibration errors, significantly improving the accuracy and stability of wavefront phase measurement.

[0025] In summary, this application, through the synergistic optimization design of beam modulation and interferometry, improves both the adaptability of the equipment to different scenarios and the energy utilization rate, while also achieving a dual improvement in detection efficiency and measurement accuracy. This significantly enhances the performance and stability of wavefront detection, enabling it to better meet the application needs of complex dynamic scenarios such as precision optical inspection and observation in highly turbulent environments. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of an embodiment of the four-wave phase-shifting point diffraction interferometer used for wavefront detection in this application;

[0028] Figure 2 The phase diagram of the checkerboard phase grating in the embodiment of the four-wave phase-shifting point diffraction interferometer used for wavefront detection in this application;

[0029] Figure 3 The phase diagram of the four-part phase plate in an embodiment of the four-wave phase-shifting point diffraction interferometer used for wavefront detection in this application is shown.

[0030] Figure 4 The present invention relates to an embodiment of a four-wave phase-shifting diffraction interferometer for wavefront detection, which includes a near-field light intensity distribution map of a strongly turbulent wavefront under test and an interferogram of the photodetector target surface. Figure 4 (a) shows the near-field light intensity distribution of the incident distorted wavefront. Figure 4 (b) is the interference pattern of the photodetector target surface;

[0031] Figure 5 The wavefront reconstruction results are shown for the incident distorted wavefront, where Figure 5 (a) shows the far-field light intensity distribution after wavefront reconstruction using the four-wave phase-shifting point diffraction interferometer for wavefront detection in this application. Figure 5 (b) shows the far-field light intensity distribution after wavefront reconstruction using the traditional Shak-Hartmann wavefront sensor mode method. Figure 5 (c) represents the far-field light intensity distribution of the incident distorted wavefront. Figure 5 (d) represents the far-field light intensity distribution of the wavefront reconstruction under ideal conditions.

[0032] Reference numerals: 1. Beam splitting module; 2. Test arm modulation module; 3. Reference arm modulation module; 4. Beam combining interference module; 5. Detection and restoration module; 201. First focusing lens; 202. Plane mirror; 203. Beam splitting grating; 204. First collimating lens; 301. Second focusing lens; 302. Plane mirror; 303. Filter; 304. Second collimating lens; 305. Partitioned fixed phase modulation element. Detailed Implementation

[0033] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0034] A four-wave phase-shifting point diffraction interferometer for wavefront detection according to an embodiment of this application will now be described in detail with reference to the accompanying drawings. Figure 1 This is a schematic diagram of an embodiment of the four-wave phase-shifting point diffraction interferometer used for wavefront detection in this application. Figure 1 As shown, the four-wave phase-shifting point diffraction interferometer for wavefront detection includes: a beam splitting module 1, a test arm modulation module 2, a reference arm modulation module 3, a beam combining interferometer module 4, and a detection restoration module 5.

[0035] The beam splitting module 1 includes a beam splitter for splitting the incident distorted wavefront into a test arm beam and a reference arm beam, wherein the test arm beam is the beam to be tested and the reference arm beam is the reference beam.

[0036] The test arm modulation module 2 is sequentially provided with a first focusing lens 201, a plane mirror 202, a beam splitter 203, and a first collimating lens 204. The beam to be tested, located at the front focal plane of the first focusing lens 201, is focused by the first focusing lens 201 and then incident on the beam splitter 203 located at the rear focal plane of the first focusing lens 201. After modulation, four diffracted beams at different angles are generated. The diffracted beams are collimated by the first collimating lens 204 and then transmitted to the beam combining interference module 4.

[0037] The reference arm modulation module 3 is sequentially provided with a second focusing lens 301, a plane mirror 302, a filter 303, a second collimating lens 304, and a partitioned fixed phase modulation element 305. The reference beam located at the front focal plane of the second focusing lens 301 is focused by the second focusing lens 301 and then incident on the filter 303 located at the rear focal plane of the second focusing lens 301. After modulation, an ideal spherical reference wavefront is generated. The ideal spherical reference wavefront is collimated by the second collimating lens 304 and partitioned fixed phase modulated by the partitioned fixed phase modulation element 305 before being transmitted to the beam combining interference module 4.

[0038] The beam combining interference module 4 includes a beam splitter, which is used to combine the beams output by the test arm modulation module 2 and the reference arm modulation module 3 to form four interference spots.

[0039] The detection and restoration module 5 includes a photodetector and a data processing unit. The photodetector acquires images of the four interference spots, and the data processing unit obtains the wavefront phase of the incident distortion wavefront based on the images of the four interference spots through a winding phase extraction algorithm and a dewinding algorithm.

[0040] The optical axis of the four-wave phase-shifting point diffraction interferometer used for wavefront detection is determined by the line connecting the optical center of the first focusing lens 201 and the optical center of the first collimating lens 204, and the line connecting the optical center of the second focusing lens 301 and the optical center of the second collimating lens 304. The optical centers of the first focusing lens 201, the first collimating lens 204, the second focusing lens 301, and the second collimating lens 304 are all aligned with the optical axis of the system.

[0041] The rear focal plane of the first focusing lens 201 completely overlaps with the front focal plane of the first collimating lens 204. The beam splitter grating 203 is placed at the overlap of the rear focal plane of the first focusing lens 201 and the front focal plane of the first collimating lens 204. The optical centers of the first focusing lens 201 and the first collimating lens 204 are both aligned with the optical axis of the system. The focal length ratio of the first focusing lens 201 to the first collimating lens 204 can be 1:1, 2:1, or other ratios.

[0042] The rear focal plane of the second focusing lens 301 completely overlaps with the front focal plane of the second collimating lens 304. The filter 303 is placed at the point where the rear focal plane of the second focusing lens 301 overlaps with the front focal plane of the second collimating lens 304. The optical centers of the second focusing lens 301 and the second collimating lens 304 are aligned with the optical axis of the system. The focal length ratio of the second focusing lens 301 and the second collimating lens 304 can also be 1:1, 2:1, or other ratios.

[0043] The beam splitter 203 is used to spatially split the test arm beam, generating four sub-beams to be tested. The beam splitter 203 can be a checkerboard phase grating, or a blazed grating, amplitude-type beam splitter grating, holographic beam splitter, or other elements with equivalent spatial splitting capabilities. The period length of the beam splitter 203... With the first diffraction angle The relationship satisfies: ,in For the operating wavelength, , The diameter of the incident pupil. The focal length of the first focusing lens 201 This refers to the size of the receiving surface of the photodetector. The focal length of the first collimating lens 204 is... The diameter of the diffraction spot on the back focal plane of the first collimating lens 204 is given, which enables the four diffraction spots to be independent of each other and allows the subsequent photodetector to obtain complete interference information.

[0044] In one possible implementation, the beam splitter grating 203 is a checkerboard phase grating, which is a binary phase modulation plate, and the phase shift function of the checkerboard phase grating is... :

[0045] , where the symbol Indicates rounding down. The grating period of the chessboard phase grating is given. The coordinates of the phase grating in the plane are Cartesian coordinates. For any integer, based on the phase shift function, the grating plane of the chessboard phase grating forms a chessboard-like phase distribution with alternating "0-π" phases, such as... Figure 2 As shown. The transmittance function of the chessboard phase grating. The Fourier transform calculation yields the following: ,in, Represents the two-dimensional Fourier transform operator. They are respectively Diffraction order in direction Represents the Fourier coefficients. Indicates an index. Let be the grating phase shift function of the chessboard phase grating. For the Dirac function, For corresponding Spatial frequency in the axial direction, For corresponding Spatial frequency in the axial direction.

[0046] Therefore, the Fourier transform of the transmittance function of the chessboard phase grating is expressed as:

[0047] ,

[0048] From the above formula, it can be seen that the chessboard phase grating does not have zero-order or even-order diffraction orders, and its first-order diffraction ( The efficiency is approximately 16.2%, and the higher-order diffraction coefficients are extremely small and negligible, thus effectively avoiding crosstalk between the four diffraction spots. After phase modulation by a checkerboard phase grating, the beam under test passes through the first collimating lens 204 and forms multiple odd-order diffraction spots on its rear focal plane. Specifically, the complex amplitude distribution of the incident distorted wavefront on its rear focal plane after passing through the first focusing lens 201 can be expressed as:

[0049] ,in, The complex amplitude distribution of the incident distorted wavefront. for The complex amplitude distribution at the rear focal plane of the first focusing lens 201 after passing through the first focusing lens 201. The focal length of the first collimating lens 204 is... The focal length of the first focusing lens 201 For the operating wavelength, The coordinates are the rectangular coordinates in the rear focal plane of the first focusing lens 201. The coordinates are rectangular coordinates within the back focal plane of the first collimating lens 204. For function The result of the two-dimensional Fourier transform. After being modulated by the chessboard phase grating, the signal is transmitted to the back focal plane of the first collimating lens 204, resulting in:

[0050] ,in, express function, for The complex amplitude distribution at the back focal plane of the first collimating lens 204 shows that the four first-order diffraction (m=±1, n=±1) spots only underwent rotational symmetry and proportional scaling operations on the incident distortion wavefront, thus completely preserving the incident distortion wavefront. The phase and amplitude information, and there is a phase difference of half a wavelength between the two sets of diagonally opposite light spots.

[0051] Filter 303 is used to filter high-frequency aberrations of the distorted wavefront, generating a high-quality ideal spherical reference wavefront. In one possible implementation, filter 303 is a pinhole filter, wherein the pinhole diameter of the pinhole filter is... ,in, For the operating wavelength, The focal length of the second focusing lens 301 The center of the pinhole filter's aperture is aligned with the focal point of the image formed by the second focusing lens 301, serving as the entrance pupil diameter. The filter 303 can also employ other types of components capable of achieving the same function of "filtering out high-frequency aberrations and generating an ideal spherical reference wavefront".

[0052] The partitioned fixed-phase modulation element 305 is used to perform partitioned phase modulation on the collimated reference beam, so that the reference beam and the four test sub-beams form an interference signal with a fixed phase difference. The partitioned fixed-phase modulation element 305 is located after the second collimating lens 304, and the system optical axis passes through the center of the partitioned fixed-phase modulation element 305. The horizontal position of the partitioned fixed-phase modulation element 305 can be flexibly set. In one possible embodiment, the partitioned fixed-phase modulation element 305 is a four-part phase plate, which is divided into four quadrants according to a rectangular coordinate system. The phase differences δ of the four quadrants are 0, π / 2, π, and 3π / 2, respectively. Figure 3 As shown. The partitioned fixed phase modulation element 305 can also be other types of elements that can achieve the same partitioned fixed phase modulation function, such as holographic phase plates, coated phase elements, etc.

[0053] In the detection and restoration module 5, the photodetector can be a CCD, CMOS, or other array-type detector. The wavefront restoration method that the data processing unit can use includes all wavefront reconstruction algorithms based on multi-frame phase-shifting interferograms and all unwinding algorithms used for winding phase restoration.

[0054] Based on the four-wave phase-shifting point diffraction interferometer for wavefront detection proposed in this application, the wavefront recovery process is as follows:

[0055] Step 1, beam splitting modulation and beam combining interference process. Specifically, the incident distortion wavefront (e.g. Figure 4 (as shown in (a)) After being split by the beam splitting module 1, the beams enter the test arm modulation module 2 and the reference arm modulation module 3 for targeted modulation. The reference arm modulation module 3 is used to generate an ideal reference beam. The filter 303 can be a pinhole filter, and the pinhole diameter of the pinhole filter is not greater than the Airy disk radius (Airy disk diameter = ,in For the operating wavelength, The focal length of the second focusing lens 301 The pinhole filter (with an incident pupil diameter) efficiently filters out high-frequency information and irregular disturbances in the incident distorted wavefront. After diffraction by the pinhole filter, the beam exhibits spherical divergence with excellent phase distribution uniformity, meeting the core requirement of phase consistency for an ideal reference beam. The spherical wave diffracted by the pinhole filter is then collimated by the second collimating lens 304, ultimately generating an ideal planar reference beam with good wavefront flatness and no additional distortion. Then, a partitioned fixed phase is applied by the partitioned fixed phase modulation element 305. The partitioned fixed phase modulation element 305 can be a four-part phase plate to generate four reference beams with phase differences of 0, π / 2, π, and 3π / 2, respectively. , , and The test arm modulation module 2 achieves spatial beam splitting through the beam splitter grating 203, while completely preserving the phase and amplitude information of the beam under test. The beam splitter grating 203 can be a checkerboard phase grating, generating four sub-beams under test. The four sub-beams under test that are transmitted to the photodetector target surface are defined as follows: and They are all scaled proportionally to the incident distorted wavefront:

[0056] , ,

[0057] , ;

[0058] The four test sub-beams from the test arm modulation module 2 and the four phase-modulated reference beams from the reference arm modulation module 3 are combined by the beam combining interference module 4, ultimately forming four phase-shifted interference spots with clear outlines and stable contrast on the photodetector target surface of the detection and restoration module 5. Figure 4 As shown in (b).

[0059] Step 2, Interference Image Acquisition and Segmentation. Specifically, the photodetector acquires the interference image after beam combining in a single step, obtaining an original image containing four sets of circular interference spots. This is based on the complex amplitude distribution function of the incident distorted wavefront after passing through the test arm modulation module 2. It can obtain the offset distance of the four primary light spots relative to the system optical axis. Spot radius Based on this, the data processing unit segments the interferometric image acquired by the photodetector to obtain four phase-shifted interferometric images. and , No. A phase-shifting interference image The expression is: ,in, Background light intensity, To interfere with the emphasis on the system, Let n be the phase of the nth sub-beam to be tested. Let be the phase of the nth reference beam, where Indicates the argument of a complex number. The phase difference between the two interfering beams (the beam under test and the reference beam) directly contains the phase information of the beam under test. Since the reference beam is an ideal plane wave, therefore... It is approximately a constant function.

[0060] Step 3, Phase Extraction and Wavefront Reconstruction. Specifically, after acquiring four phase-shifting interferometric images, the entanglement phase is calculated using a phase-shifting interferometric phase extraction algorithm. :

[0061] Since the phase-shifting interferometry phase extraction algorithm is expressed in the form of the arctangent function, the calculated entangled phase is... The range is The phase unwrapping can be performed using the Goldstein algorithm to obtain the phase of the incident distorted wavefront. .

[0062] The following example illustrates the effectiveness of the four-wave phase-shifting point diffraction interferometer for wavefront detection described in this application. For instance, in the four-wave phase-shifting point diffraction interferometer for wavefront detection described in this application, the period length of the checkerboard phase grating is 51.2 μm, the focal length of the first focusing lens is 140 mm, the focal length of the first collimating lens is 35 mm, the focal length of the second focusing lens is 70 mm, the focal length of the second collimating lens is 35 mm, and the photodetector is a CCD detector with a pixel size of 6.4 μm. The operating wavelength is 635 nm. The far-field light intensity distribution after the incident distorted wavefront is restored by the four-wave phase-shifting point diffraction interferometer for wavefront detection described in this application is as follows: Figure 5 As shown in (a) (far-field Strehl ratio of 0.67286), it can be seen from the figure that, compared with Figure 5 Compared to the far-field intensity distribution of the incident distorted wavefront shown in (c), the far-field intensity energy distribution after processing by the four-wave phase-shifting point diffractometer used for wavefront detection in this application is more concentrated, and is consistent with... Figure 5 The far-field intensity distribution of the wavefront reconstruction shown in (d) is close to that in the ideal case, indicating that the four-wave phase-shifting diffraction interferometer for wavefront detection provided in this application embodiment achieves good reconstruction of the strongly turbulent distorted wavefront. To highlight the advantages of the four-wave phase-shifting diffraction interferometer for wavefront detection in this application, under the same conditions, the far-field intensity distribution after wavefront reconstruction is obtained using the traditional Shake-Hartmann wavefront sensor mode method with an 8×8 sub-aperture array, as shown in (d). Figure 5 As shown in (b) (far-field Strehl ratio of 0.21989), it can be seen from the figure that the far-field light intensity energy distribution is still very scattered, compared to... Figure 5 The similar far-field intensity distribution of the incident distortion wavefront shown in (c) indicates that the incident distortion wavefront was not effectively recovered. The above results fully demonstrate that the four-wave phase-shifting point diffraction interferometer used for wavefront detection in this application can effectively recover the incident distortion wavefront in a strongly turbulent scenario, which is significantly better than the traditional Shak-Hartmann wavefront sensor.

[0063] According to the embodiments of this application, a four-wave phase-shifting point diffraction interferometer for wavefront detection splits the incident beam into four diffracted beams at different angles by setting a beam-splitting grating on the focal plane behind the first focusing lens. After being collimated by the first collimating lens, a small-aperture, crosstalk-free fine beam is output. Adjusting the focal length of the two lenses can flexibly adapt to the beam-shrinking ratio to meet different turbulence intensities and detection accuracy requirements, improving the adaptability and flexibility of the equipment. The beam-splitting grating is based on phase modulation beam splitting, with no additional light absorption, high energy utilization, and minimal impact from environmental factors such as temperature and humidity, making it suitable for complex working conditions. Furthermore, by setting a partitioned fixed phase modulation element behind the second collimating lens, partitioned phase modulation is applied to the reference wavefront, forming spatial phase-shifting interference with the four fine beams. Four different phase-shifting interferograms can be obtained in a single measurement, significantly improving detection efficiency. In addition, various time-domain phase-shifting errors can be avoided without moving parts and complex calibration, improving measurement accuracy and stability. The four-wave phase-shifting point diffraction interferometer for wavefront detection provided in this application embodiment, through collaborative optimization design, can simultaneously improve equipment adaptability, energy utilization, detection efficiency and measurement accuracy, significantly enhance the performance and stability of wavefront detection, and meet the needs of complex dynamic scenarios.

[0064] All of the above-mentioned optional technical solutions can be combined in any way to form the optional embodiments of this application, and will not be described in detail here.

[0065] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A four-wave phase-shift point-diffraction interferometer for wavefront detection, characterized in that, include: The module consists of a beam splitting module (1), a test arm modulation module (2), a reference arm modulation module (3), a beam combining interference module (4), and a detection and restoration module (5). The beam splitting module (1) includes a beam splitter for splitting the incident distorted wavefront into a test arm beam and a reference arm beam, wherein the test arm beam is the beam to be tested and the reference arm beam is the reference beam. The test arm modulation module (2) is sequentially provided with a first focusing lens (201), a plane mirror (202), a beam splitter (203), and a first collimating lens (204); The reference arm modulation module (3) is provided with a second focusing lens (301), a plane mirror (302), a filter (303), a second collimating lens (304), and a partitioned fixed phase modulation element (305) in sequence; The beam combining interference module (4) includes a beam splitter, which is used to combine the beams output by the test arm modulation module (2) and the reference arm modulation module (3) to form four interference spots; The detection and restoration module (5) includes a photodetector and a data processing unit. The photodetector acquires images of the four interference spots, and the data processing unit obtains the wavefront phase of the incident distortion wavefront based on the images of the four interference spots through a winding phase extraction algorithm and a dewinding algorithm. The optical axis of the four-wave phase-shifting point diffraction interferometer used for wavefront detection is determined by the line connecting the optical centers of the first focusing lens (201) and the first collimating lens (204), and the line connecting the optical centers of the second focusing lens (301) and the second collimating lens (304). The optical centers of the first focusing lens (201), the first collimating lens (204), the second focusing lens (301), and the second collimating lens (304) are all aligned with the optical axis of the system.

2. The four-wave phase-shifting point diffractometer for wavefront detection according to claim 1, characterized in that, The beam to be tested, located on the front focal plane of the first focusing lens (201), is focused by the first focusing lens (201) and then incident on the beam splitter (203) located on the rear focal plane of the first focusing lens (201). After modulation, four diffracted beams at different angles are generated. The diffracted beams are collimated by the first collimating lens (204) and then transmitted to the beam combining interference module (4). The reference beam located at the front focal plane of the second focusing lens (301) is focused by the second focusing lens (301) and then incident on the filter (303) located at the rear focal plane of the second focusing lens (301). After modulation, an ideal spherical reference wavefront is generated. The ideal spherical reference wavefront is collimated by the second collimating lens (304) and modulated by the partitioned fixed phase modulation element (305) before being transmitted to the beam combining interference module (4).

3. The four-wave phase-shift point-diffraction interferometer for wavefront probing according to claim 2, characterized in that, The rear focal plane of the first focusing lens (201) completely overlaps with the front focal plane of the first collimating lens (204). The beam splitter (203) is placed at the point where the rear focal plane of the first focusing lens (201) overlaps with the front focal plane of the first collimating lens (204), and the optical centers of the first focusing lens (201) and the first collimating lens (204) are both aligned with the optical axis of the system.

4. The four-wave phase-shift point-diffraction interferometer for wavefront probing according to claim 2, characterized in that, The rear focal plane of the second focusing lens (301) completely overlaps with the front focal plane of the second collimating lens (304). The filter (303) is placed at the point where the rear focal plane of the second focusing lens (301) overlaps with the front focal plane of the second collimating lens (304), and the optical centers of the second focusing lens (301) and the second collimating lens (304) are aligned with the optical axis of the system.

5. The four-wave phase-shifting point diffractometer for wavefront detection according to claim 2, characterized in that, Period length of the beam splitter grating (203) With the first diffraction angle The relationship is: ,in For the operating wavelength, , The diameter of the incident pupil. The focal length of the first focusing lens (201) is... This refers to the size of the receiving surface of the photodetector. The focal length of the first collimating lens (204) is... The diameter of the diffraction spot on the back focal plane of the first collimating lens (204) is denoted as .

6. The four-wave phase-shifting point diffractometer for wavefront detection according to claim 5, characterized in that, The beam splitter grating (203) is a checkerboard phase grating, which is a binary phase modulation plate, and the phase shift function of the checkerboard phase grating is... , where the symbol This indicates rounding down. The grating period of the chessboard phase grating is given by [reference to grating period]. The coordinates of the phase grating in the plane are Cartesian coordinates. For any integer, based on the phase shift function, the grating plane of the chessboard phase grating forms a chessboard-like phase distribution with alternating "0-π" values.

7. The four-wave phase-shifting point diffractometer for wavefront detection according to claim 6, characterized in that, The Fourier transform of the transmittance function of the chessboard phase grating is expressed as: ， in, The coordinates of the phase grating in the plane are Cartesian coordinates. Let be the transmittance function of the chessboard phase grating. Corresponding to shaft and Diffraction orders along the axial direction Represents the two-dimensional Fourier transform operator. Represents the Dirac function, For corresponding Spatial frequency in the axial direction, For corresponding Spatial frequency in the axial direction.

8. The four-wave phase-shifting point diffractometer for wavefront detection according to claim 7, characterized in that, ,in, The coordinates are the rectangular coordinates in the back focal plane of the first collimating lens (204). The complex amplitude distribution of the incident distorted wavefront. for The complex amplitude distribution at the back focal plane of the first collimating lens (204) ， in, The coordinates are rectangular coordinates in the back focal plane of the first focusing lens (201). The complex amplitude distribution of the incident distorted wavefront. for The complex amplitude distribution at the rear focal plane of the first focusing lens (201) after passing through the first focusing lens (201). The focal length of the first collimating lens (204) is... The focal length of the first focusing lens (201) is... For the operating wavelength, For function The two-dimensional Fourier transform result, Indicates an index. After being modulated by the chessboard phase grating, it is transmitted to the back focal plane of the first collimating lens (204).

9. The four-wave phase-shifting point diffractometer for wavefront detection according to any one of claims 2-8, characterized in that, The filter (303) is a pinhole filter, wherein the pinhole diameter of the pinhole filter is... ,in For the operating wavelength, The focal length of the second focusing lens (301) is... The center of the pinhole filter aperture is aligned with the focal point of the second focusing lens (301) after imaging, which is the entrance pupil aperture.

10. The four-wave phase-shifting point diffractometer for wavefront detection according to any one of claims 2-8, characterized in that, The partitioned fixed phase modulation element (305) is a four-part phase plate. The four-part phase plate is divided into four quadrants according to the rectangular coordinate system. The phase differences of the four quadrants are 0, π / 2, π and 3π / 2 respectively. The partitioned fixed phase modulation element (305) is located after the second collimating lens (304), and the optical axis of the system passes through the center of the partitioned fixed phase modulation element (305).

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