Wavefront gradient feature matching-based absolute detection center alignment method for surface shape and optical system

Abstract

The application provides a wave front gradient feature matching-based surface shape absolute detection center alignment method and an optical system, and relates to the technical field of optics. The method comprises the following steps: obtaining initial surface shape data of a detected optical element and corresponding surface shape data at multiple rotation angles; performing two-dimensional gradient calculation on the filtered surface shape data to obtain two-dimensional total gradient data with multiple feature mark point distributions; obtaining accurate positioning coordinates of each feature mark point; obtaining a rotation center coordinate of the detected optical element; obtaining a center pixel coordinate of a standard reference mirror; and adjusting the detected optical element according to the rotation center coordinate of the detected optical element and the center pixel coordinate of the standard reference mirror to align the detected optical element with the standard reference mirror. The application is mainly used for solving the problem of high-precision alignment between the center of the detected optical element and the center of the reference surface optical axis before the rotation and translation operation of the optical element surface shape absolute detection, and has the characteristics of simple method principle, high precision, high efficiency and convenience.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and more specifically, to a method and optical system for aligning the absolute detection center of a surface shape based on wavefront gradient feature matching. Background Technology

[0002] With the rapid development of modern optical technology, the requirements for the surface accuracy of optical components are becoming increasingly stringent. Precise inspection technology is a prerequisite for the precision manufacturing of optical components. The surface shape of optical components is often inspected using interferometers, but its accuracy is limited by systematic errors such as the accuracy of the reference surface. Absolute surface shape inspection technology is an effective means to improve the accuracy of surface shape inspection. This technology often involves multiple rotations and translations of the optical component under inspection relative to a standard reference mirror in different orientations to obtain a series of misaligned and superimposed wavefront data. Then, the absolute surface shape information of the inspected surface can be obtained through wavefront calculation algorithms.

[0003] Absolute inspection techniques typically require rotating the optical element under test multiple times around its optical axis relative to a standard reference mirror to check its surface shape. During these multiple rotations, the center of the optical element under test must be precisely aligned with the center of the optical axis of the reference surface. Alignment errors can lead to misalignment and superposition of the wavefronts between the tested and reference wavefronts. The wavefront inspections from multiple rotations accumulate errors, ultimately significantly impacting the accuracy of the absolute surface shape calculation.

[0004] Currently, the common method for achieving center alignment involves determining a feature marker on the surface of the optical component under inspection. This marker may be specifically manufactured or be a dust defect present on the component's surface. At different rotation angles, the pixel coordinates of this marker within the inspection field of view are tracked and recorded. A fitted circle is then obtained using these pixel coordinates to determine the rotation center pixel coordinates of the component. Therefore, this method is cumbersome in firstly because determining the feature marker is complex, and a single feature marker may occupy multiple pixels in the image, leading to positioning errors. Secondly, at different rotation angles, it is often necessary to track, determine, and record the pixel coordinates of the feature marker step by step. Furthermore, the extraction of the feature marker is affected by low-frequency surface shape information, resulting in inaccurate positioning of individual pixel coordinates. Ultimately, this affects the achievement of high-precision center alignment, resulting in low efficiency. Summary of the Invention

[0005] The present invention aims to provide, for example, a method and optical system for aligning the center of an absolute surface detection device based on wavefront gradient feature matching. This method is mainly used to solve the problem of high-precision alignment between the center of the optical element under test and the optical axis center of the reference surface before the rotation and translation operation of the absolute surface detection of optical elements. It features a simple principle, high precision, high efficiency and convenience.

[0006] The embodiments of the present invention can be implemented as follows:

[0007] In a first aspect, embodiments of the present invention provide a method for aligning the absolute detection center of a surface shape based on wavefront gradient feature matching, used for aligning an optical element under test, the method comprising:

[0008] Obtain the initial surface shape data of the optical element under test;

[0009] Acquire the surface shape data of the optical element under test at multiple rotation angles, wherein the surface shape data corresponding to the multiple rotation angles are the surface shape data of the optical element under test rotating relative to the standard reference mirror at multiple angles;

[0010] The initial surface data and the surface data corresponding to multiple rotation angles are filtered.

[0011] Two-dimensional gradient calculations are performed on the filtered surface data to obtain two-dimensional total gradient data with multiple feature marker point distributions;

[0012] Based on the two-dimensional total gradient data with multiple feature marker points distributed, the precise positioning coordinates of each feature marker point are obtained;

[0013] Based on the precise positioning coordinates of each feature marker point, the rotation center coordinates of the inspected optical element are obtained;

[0014] In the interferometer's detection field of view, the center pixel coordinates of the standard reference mirror are obtained;

[0015] The optical element under test is adjusted according to the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror so that the optical element under test is aligned with the standard reference mirror.

[0016] Furthermore, in an optional embodiment, in the step of acquiring the initial surface shape data of the optical element under test, in the interferometer detection field of view, the standard reference mirror and the aperture of the optical element under test are substantially coincident, and after the standard reference mirror and the optical element under test are adjusted to zero fringes, the initial surface shape data of the optical element under test is obtained.

[0017] Further, in an optional embodiment, the optical element under test is connected to a rotating device, which is used to rotate the optical element under test relative to the standard reference mirror. In the step of obtaining the surface shape data of the optical element under test at multiple rotation angles, the optical element under test is rotated relative to the standard reference mirror at multiple angles by the rotating device, and after the standard reference mirror and the optical element under test are adjusted to zero fringes, the surface shape data of the optical element under test at each rotation angle is measured to obtain the surface shape data corresponding to the multiple rotation angles.

[0018] Further, in an optional embodiment, the step of filtering the initial surface data and the surface data corresponding to the plurality of rotation angles includes: performing bandpass filtering on the initial surface data and the surface data corresponding to the plurality of rotation angles to retain the mid-to-high frequency information in the surface data.

[0019] Further, in an optional embodiment, the step of performing two-dimensional gradient calculation on the filtered surface data to obtain two-dimensional total gradient data with multiple feature marker point distributions includes:

[0020] Gradient calculations are performed in the x and y directions for each surface data after filtering.

[0021] The two-dimensional total gradient data with multiple feature marker point distributions is calculated using the following formula:

[0022]

[0023] In the formula, G n (x,y) represents the two-dimensional total gradient data, G xn (x,y) represents the gradient of the surface data in the x-direction, G yn (x,y) represents the gradient of the surface data in the y direction.

[0024] Further, in an optional embodiment, the step of obtaining the precise positioning coordinates of each feature marker point based on the two-dimensional total gradient data having a distribution of multiple feature marker points includes:

[0025] Based on the two-dimensional total gradient data with multiple feature marker points distributed, the feature marker points are identified and located to obtain the position information of each feature marker point;

[0026] Based on the location information of the feature markers, the multiple feature markers are matched, located, and extracted to obtain the precise location coordinates of each feature marker.

[0027] Further, in an optional embodiment, the step of obtaining the rotation center coordinates of the inspected optical element based on the precise positioning coordinates of each feature marker point includes:

[0028] Among the plurality of feature markers, select one feature marker with a matching degree greater than a preset value;

[0029] The rotation center coordinates of the inspected optical element are obtained by performing a least-squares circular fit on the precise positioning coordinates of the feature marker point in each two-dimensional total gradient data.

[0030] Further, in an optional embodiment, the step of obtaining the center pixel coordinates of the standard reference mirror in the interferometer detection field of view includes:

[0031] A subpixel edge localization extraction box is determined in the imaging edge region of the standard reference mirror;

[0032] The edge region to be located by subpixel edge localization extraction box is selected.

[0033] The extracted sub-pixel edge coordinates are fitted with a least-squares circle to obtain the center coordinates of the circle, which are the center pixel coordinates of the standard reference mirror.

[0034] Further, in an optional embodiment, the step of adjusting the optical element under test according to the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror to align the optical element under test with the standard reference mirror includes:

[0035] Calculate the deviation distance Δx in the x-direction and the deviation distance Δy in the y-direction between the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror in the field of view of the interferometer;

[0036] The optical element under test is translated by Δx in the x-direction and Δy in the y-direction to align it with the standard reference mirror.

[0037] In a second aspect, embodiments of the present invention provide an optical system for implementing the surface absolute detection center alignment method based on wavefront gradient feature matching of any of the foregoing claims. The surface absolute detection center alignment device includes: a laser, a collimating and beam expanding system, a standard reference mirror, a rotating device, an adjustment mechanism, and a CCD image acquisition system.

[0038] The standard reference mirror is positioned between the optical element under test and the collimation and beam expansion system. The light emitted by the laser passes through the collimation and beam expansion system and the standard reference mirror and enters the optical element under test. The reference wavefront reflected by the standard reference mirror and the test wavefront reflected by the optical element under test generate coherent superimposed fringes on the CCD camera image acquisition system. The CCD camera image acquisition system is also used to transmit the acquired interference fringe data to a computer.

[0039] The optical element under test is connected to the rotating device, which is connected to the adjusting mechanism. The rotating device is used to adjust the rotation angle of the optical element under test relative to the standard reference mirror, and the adjusting mechanism is used to adjust the zeroing stripe and translation of the optical element under test relative to the standard reference mirror.

[0040] The method and optical system for absolute surface shape detection based on wavefront gradient feature matching provided by this invention are mainly used to solve the problem of high-precision alignment between the center of the optical element under test and the optical axis center of the reference surface before rotation and translation operations in absolute surface shape detection of optical elements. The method is simple in principle, highly precise, efficient, intelligent and convenient. First, by utilizing the features and distribution characteristics of the measured wavefront surface shape data, the mid-to-high frequency information in the surface shape is highlighted through frequency domain filtering and gradient calculation, forming feature marker points. There is no need to make specific marks on the surface of the element or seek marker points. Second, using image recognition matching algorithms in computer vision image processing technology, the feature marker points in the wavefront gradient image are adaptively identified and highly precisely located. Through matching algorithms, highly matching feature marker points between images are extracted to track the trajectory coordinates of feature points during rotation in an intelligent and more precise manner. Furthermore, sub-pixel edge extraction technology is used to achieve more accurate positioning and extraction of the reference surface center pixel coordinate information, further realizing efficient and high-precision correction of the rotation center of the optical element, effectively suppressing the influence of such error factors on the accuracy of absolute surface shape detection. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as limiting the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the surface absolute detection center alignment device based on wavefront gradient feature matching according to a specific embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the surface absolute detection center alignment method based on wavefront gradient feature matching according to a specific embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the interferometer surface shape detection according to a specific embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the feature marker point pair described in a specific embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram of the subpixel edge extraction frame (ROI) according to a specific embodiment of the present invention.

[0047] Icons: 1-Laser; 2-Collimation and beam expansion system; 3-Standard reference mirror; 4-Optical element under test; 5-Rotation device; 6-Adjustment mechanism; 7-CCD image acquisition system; 11-Interferometer detection field of view; 12-Reference surface field of view area; 13-Initially measured surface area; 14-Surface area measured after rotation; 21-Feature marker pairs with high matching degree in images at different rotation angles; 22-Multiple feature points automatically identified in images at different rotation angles; 31-Interferometer detection field of view; 32-Reference surface area; 33-Reference surface center (xr, yr); 34-Subpixel edge extraction box (ROI); 35-Subpixel positioning edge of the reference surface. Detailed Implementation

[0048] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0049] 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.

[0050] Therefore, the following detailed description of the embodiments of the 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 invention without inventive effort are within the scope of protection of the invention.

[0051] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0052] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0053] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0054] Please see Figure 1 and Figure 2 This embodiment provides a method and optical system for aligning the center of an absolute surface detection based on wavefront gradient feature matching. It is mainly used to solve the problem of high-precision alignment between the center of the optical element under test and the center of the optical axis of the reference surface before the rotation and translation operation of the absolute surface detection of optical elements. It has the characteristics of simple principle, high precision, high efficiency and convenience.

[0055] like Figure 1 As shown in this embodiment of the invention, the optical system for implementing the surface absolute detection center alignment method based on wavefront gradient feature matching includes: a laser, a collimating and expanding system, a standard reference mirror, a rotating device, an adjustment mechanism, and a CCD image acquisition system. The standard reference mirror is disposed between the optical element under test and the collimating and expanding system. Light emitted from the laser passes through the collimating and expanding system and the standard reference mirror and enters the optical element under test. The reference wavefront reflected by the standard reference mirror and the test wavefront reflected by the optical element under test generate coherent superimposed fringes on the CCD camera image acquisition system. The CCD camera image acquisition system is also used to transmit the acquired interference fringe data to a computer. The optical element under test is connected to the rotating device, and the rotating device is connected to the adjustment mechanism. The rotating device is used to adjust the rotation angle of the optical element under test relative to the standard reference mirror, and the adjustment mechanism is used to adjust and translate the zeroing fringes of the optical element under test relative to the standard reference mirror.

[0056] It should be noted that, in this embodiment of the invention, the light emitted by the laser passes through a collimation and beam-expanding system to form collimated light of a certain aperture. This collimated light then passes through a standard reference mirror and is incident on the surface of the optical element under test. The reference wavefront reflected by the standard reference mirror and the test wavefront, respectively, and the test wavefront ultimately produce coherent superimposed fringes on the CCD camera. These fringes are adjusted to zero by an adjustment mechanism, and the interference fringe pattern is acquired by the CCD image acquisition system and sent to a computer for corresponding data processing. This embodiment of the invention can be performed without any auxiliary devices, and the method is simple, low-cost, and has few sources of error.

[0057] like Figure 2 As shown, the surface absolute detection center alignment method based on wavefront gradient feature matching includes the following steps:

[0058] Step S100: Obtain the initial surface shape data of the optical element under test.

[0059] It should be noted that in step S100, in the interferometer detection field of view (e.g. Figure 3 As shown, after aligning the standard reference mirror and the optical element under test to zero fringes, the initial surface shape data of the optical element under test is obtained. The initial surface shape data can be denoted as W0(x, y).

[0060] Step S200: Obtain the surface shape data of the optical element under test at multiple rotation angles, wherein the surface shape data corresponding to the multiple rotation angles are the surface shape data of the optical element under test rotating relative to the standard reference mirror at multiple angles.

[0061] In an optional embodiment, the optical element under test is connected to a rotating device, which is used to rotate the optical element under test relative to a standard reference mirror. In step S200, which obtains the surface shape data of the optical element under test at multiple rotation angles, the optical element under test is rotated relative to the standard reference mirror by multiple angles through the rotating device. After the standard reference mirror and the optical element under test are adjusted to zero stripes, the surface shape data of the optical element under test at each rotation angle is measured, and the surface shape data corresponding to multiple rotation angles are obtained.

[0062] It should be noted that the optical element under test is rotated at least two angles relative to the standard reference mirror, which can be adjusted using a rotation device. At each rotation angle, the corresponding surface shape data W is measured. n (x, y) represents the surface shape data corresponding to the nth rotation angle (n = 1, ..., N).

[0063] Step S300: Filter the initial surface shape data and the surface shape data corresponding to multiple rotation angles. In this embodiment, bandpass filtering is performed on the initial surface shape data and the surface shape data corresponding to multiple rotation angles to retain the mid-to-high frequency information in the surface shape data. The measured surface shape data, i.e., the two-dimensional wavefront image W of the optical element under test... n (x, y) (n = 0...N) are subjected to bandpass filtering in the corresponding frequency band to retain the mid-to-high frequency information in the wavefront data.

[0064] Step S400: Perform two-dimensional gradient calculation on each surface data after filtering to obtain two-dimensional total gradient data with multiple feature marker point distributions.

[0065] Further, in an optional embodiment, the step of performing two-dimensional gradient calculation on the filtered surface data to obtain two-dimensional total gradient data with multiple feature marker point distributions includes:

[0066] Sub-step S410: Calculate the gradients in the x and y directions for each of the filtered surface data;

[0067] Sub-step S420: Calculate the two-dimensional total gradient data with multiple feature marker point distributions according to the following formula:

[0068]

[0069] In the formula, G n (x,y) represents the two-dimensional total gradient data, G xn (x,y) represents the gradient of the surface data in the x-direction, G yn (x,y) represents the gradient of the surface data in the y direction.

[0070] It should be noted that the mid-to-high frequency information present in the surface shape or the mid-to-high frequency information introduced by dust defects on the component surface are highlighted as feature markers.

[0071] Step S500: Obtain the precise positioning coordinates of each feature marker point based on the total gradient data of each two-dimensional feature marker point with multiple feature marker point distributions.

[0072] In an optional embodiment, step S500, which obtains the precise positioning coordinates of each feature marker point based on the two-dimensional total gradient data with multiple feature marker point distributions, includes sub-step S510: identifying and locating the feature marker points based on the two-dimensional total gradient data with multiple feature marker point distributions to obtain the position information of each feature marker point; and sub-step S520: matching and locating multiple feature marker points based on the position information of the feature marker points to obtain the precise positioning coordinates of each feature marker point pair.

[0073] It should be noted that in step S500, please refer to... Figure 4 The Surf (Speed ​​Up Robust Feature) algorithm, used in computer vision image processing, can be used to process the obtained two-dimensional gradient distributions G. n The feature markers on (x, y) are automatically identified, located, and described. Then, the feature markers with strong correlation and matching degree are matched, located, and extracted to obtain the feature points at different rotation angles G. n Precise location coordinates in the (x, y) image (x n y n ).

[0074] Step S600: Obtain the rotation center coordinates of the optical element under test based on the precise positioning coordinates of each feature marker point.

[0075] In an optional embodiment, step S600 of obtaining the rotation center coordinates of the optical element under test based on the precise positioning coordinates of each feature marker point includes sub-step S610: selecting a feature marker point with a matching degree greater than a preset value from multiple feature marker points; sub-step S620: performing least squares circular fitting on the precise positioning coordinates of the feature marker point in each two-dimensional total gradient data to obtain the rotation center coordinates of the optical element under test.

[0076] Step S700: Obtain the center pixel coordinates of the standard reference mirror in the interferometer detection field of view.

[0077] Further, in an optional embodiment, step S700 of obtaining the center pixel coordinates of the standard reference mirror in the interferometer detection field of view includes sub-step S710: determining a sub-pixel edge localization extraction box in the edge region of the standard reference mirror image; sub-step S720: selecting the edge region to be localized by sub-pixel localization using the sub-pixel edge localization extraction box; sub-step S730: performing least squares fitting of circles on the extracted sub-pixel edge coordinate points to obtain the center coordinates of the circle, which are the center pixel coordinates of the standard reference mirror.

[0078] It should be noted that in the interferometer detection field of view, please refer to... Figure 5 The standard reference mirror presents a circular region. A sub-pixel edge localization extraction box (ROI) is defined within the edge region. This ROI selects the edge region to be localized into sub-pixels. The extracted sub-pixel coordinates are then fitted with a least-squares circle to obtain the center coordinates, which are the center pixel coordinates (xr, yr) of the reference surface, as shown in the figure. In the figure: "31" represents the interferometer's detection field of view; "32" represents the reference surface region; "33" represents the center of the reference surface (xr, yr); "34" represents the sub-pixel edge localization box (ROI); and "35" represents the sub-pixel localization edge of the standard reference mirror.

[0079] Step S800: Adjust the optical element under test according to the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror so that the optical element under test is aligned with the standard reference mirror.

[0080] Further, in an optional embodiment, the step S800 of adjusting the optical element under test (OUT) to align it with the standard reference mirror based on the rotation center coordinates of the OUT and the center pixel coordinates of the standard reference mirror includes sub-step S810: calculating the deviation distance Δx in the x-direction and the deviation distance Δy in the y-direction between the rotation center coordinates of the OUT and the center pixel coordinates of the standard reference mirror in the interferometer field of view; sub-step S820: translating the OUT by Δx in the x-direction and Δy in the y-direction, respectively, to align the OUT with the standard reference mirror.

[0081] This invention provides a method for aligning the absolute detection center of a rotational and translational surface shape based on wavefront image gradient feature matching. It eliminates the need to specify particular feature markers, instead generating them through digital image processing. This adaptively achieves more precise image feature localization, extraction, and matching, thereby obtaining the rotation center of the inspected optical element. Furthermore, for the positioning of the reference surface center, a sub-pixel edge extraction technique is proposed to obtain a more accurate reference center, thus achieving high-precision and efficient alignment of the absolute detection center of the surface shape.

[0082] It should be noted that in existing technologies, a feature marker is determined on the surface of the component under inspection. This marker may be specifically manufactured or be a dust defect present on the component surface. At different rotation angles, the pixel coordinates of this marker within the inspection field of view are tracked and recorded. A fitted circle is then obtained using these pixel coordinates to determine the rotation center pixel coordinates of the component under inspection. Therefore, this method is cumbersome in firstly because determining the feature marker is complex, and a single feature marker may occupy multiple pixels in the image, leading to positioning errors. Secondly, at different rotation angles, it is often necessary to gradually track, determine, and record the pixel coordinates of the feature marker. Furthermore, the extraction of the feature marker is affected by low-frequency surface shape information, resulting in inaccurate pixel coordinate positioning. Ultimately, this affects the achievement of high-precision center alignment and reduces efficiency.

[0083] To achieve high-precision alignment between the optical axis center of the reference surface and the rotation center of the inspected component during the rotational translation operation for absolute detection of optical component surface shape, this invention provides a center alignment method based on wavefront image gradient feature matching technology. This addresses the problem of existing technologies where rotation center deviation or low center alignment correction accuracy affects the absolute detection accuracy of the surface shape during rotational translation. This invention utilizes the features and distribution characteristics of the measured wavefront surface shape data. Through frequency domain filtering and gradient calculation, it highlights mid-to-high frequency information in the surface shape, forming feature marker points. There is no need to create specific marks on the component surface or search for marker points. Simultaneously, it employs image recognition and matching algorithms in computer vision image processing technology to adaptively identify and precisely locate the feature marker points in the wavefront gradient image. Through matching algorithms, it extracts highly matched feature marker points between images, intelligently and with higher precision tracking of the trajectory coordinates of feature points during rotation. Furthermore, it employs sub-pixel edge extraction technology to achieve more accurate positioning and extraction of the reference surface center pixel coordinate information, further realizing efficient and high-precision correction of the optical component rotation center and effectively suppressing the impact of such error factors on the absolute detection accuracy of the surface shape. The embodiments of the present invention are mainly used to solve the problem of high-precision alignment between the center of the optical element under test and the center of the optical axis of the reference surface before the rotation and translation operation for absolute detection of the surface shape of optical elements. The method is simple in principle, highly precise, efficient, intelligent and convenient.

[0084] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for aligning the absolute detection center of an optical element based on wavefront gradient feature matching, used for aligning the optical element under test, characterized in that, The method for aligning the absolute detection center of the surface shape includes: Under zero-fringe conditions, the initial surface shape data of the optical element under test is acquired; Acquire the surface shape data of the optical element under test at multiple rotation angles, wherein the surface shape data corresponding to the multiple rotation angles are the surface shape data of the optical element under test rotating relative to the standard reference mirror at multiple angles; The initial surface shape data and the surface shape data corresponding to the multiple rotation angles are filtered. Two-dimensional gradient calculations are performed on the filtered surface data to obtain two-dimensional total gradient data with multiple feature marker point distributions; Based on the two-dimensional total gradient data with multiple feature marker points distributed, the precise positioning coordinates of each feature marker point are obtained; Based on the precise positioning coordinates of each feature marker point, the rotation center coordinates of the inspected optical element are obtained; In the interferometer's detection field of view, the center pixel coordinates of the standard reference mirror are obtained; The optical element under test is adjusted according to the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror so that the optical element under test is aligned with the standard reference mirror. The step of performing two-dimensional gradient calculation on each filtered surface data to obtain two-dimensional total gradient data with multiple feature marker points includes: performing gradient calculations in the x and y directions on each filtered surface data; and calculating the two-dimensional total gradient data with multiple feature marker points according to the following formula: In the formula, Represents the total gradient data in two dimensions. This represents the gradient of the surface data in the x-direction. This represents the gradient of the surface data in the y-direction; The step of obtaining the precise positioning coordinates of each feature marker point based on the two-dimensional total gradient data with multiple feature marker point distributions includes: identifying and locating the feature marker points based on the two-dimensional total gradient data with multiple feature marker point distributions to obtain the position information of each feature marker point; and performing matching and positioning extraction on the multiple feature marker points based on the position information of the feature marker points to obtain the precise positioning coordinates of each feature marker point. The step of obtaining the rotation center coordinates of the optical element under test based on the precise positioning coordinates of each feature marker point includes: selecting a feature marker point with a matching degree greater than a preset value from the plurality of feature marker points; performing least squares circular fitting on the precise positioning coordinates of the feature marker point in each two-dimensional total gradient data to obtain the rotation center coordinates of the optical element under test.

2. The method for absolute surface detection center alignment based on wavefront gradient feature matching according to claim 1, characterized in that, In the step of acquiring the initial surface shape data of the optical element under test, the standard reference mirror and the optical element under test are aligned to zero fringes in the interferometer detection field of view to obtain the initial surface shape data of the optical element under test.

3. The method for absolute surface detection center alignment based on wavefront gradient feature matching according to claim 1, characterized in that, The optical element under test is connected to a rotating device, which is used to rotate the optical element under test relative to the standard reference mirror. In the step of obtaining the surface shape data of the optical element under test at multiple rotation angles, the optical element under test is rotated relative to the standard reference mirror at multiple angles by the rotating device. After the standard reference mirror and the optical element under test are adjusted to zero fringes, the surface shape data of the optical element under test at each rotation angle is measured to obtain the surface shape data corresponding to the multiple rotation angles.

4. The method for absolute surface detection center alignment based on wavefront gradient feature matching according to claim 1, characterized in that, The step of filtering the initial surface shape and the surface shape data corresponding to the multiple rotation angles includes: performing bandpass filtering on the initial surface shape and the surface shape data corresponding to the multiple rotation angles to retain the mid-to-high frequency information in the surface shape data.

5. The method for absolute surface detection center alignment based on wavefront gradient feature matching according to claim 1, characterized in that, The step of obtaining the center pixel coordinates of the standard reference mirror in the interferometer detection field of view includes: Determine the subpixel edge localization extraction box in the edge region of the standard reference mirror; The edge region to be located by subpixel edge localization extraction box is selected. The extracted sub-pixel edge coordinates are fitted with a least-squares circle to obtain the center coordinates of the circle, which are the center pixel coordinates of the standard reference mirror.

6. The method for absolute surface detection center alignment based on wavefront gradient feature matching according to any one of claims 1-5, characterized in that, The step of adjusting the optical element under test according to the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror to align the optical element under test with the standard reference mirror includes: Calculate the deviation distance Δx in the x-direction and the deviation distance Δy in the y-direction between the rotation center coordinates of the optical element under test and the center pixel coordinates of the standard reference mirror in the field of view of the interferometer; The optical element under test is translated by Δx in the x-direction and Δy in the y-direction to align it with the standard reference mirror.

7. An optical system for implementing the surface absolute detection center alignment method based on wavefront gradient feature matching as described in any one of claims 1-6, characterized in that, The optical system includes: a laser, a collimating and beam expanding system, a standard reference mirror, a rotating device, an adjustment mechanism, and a CCD image acquisition system; The standard reference mirror is positioned between the optical element under test and the collimation and beam expansion system. The light emitted by the laser passes through the collimation and beam expansion system and the standard reference mirror and enters the optical element under test. The reference wavefront reflected by the standard reference mirror and the test wavefront reflected by the optical element under test generate coherent superimposed fringes on the CCD camera image acquisition system. The CCD camera image acquisition system is also used to transmit the acquired interference fringe data to a computer. The optical element under test is connected to the rotating device, which is connected to the adjusting mechanism. The rotating device is used to adjust the rotation angle of the optical element under test relative to the standard reference mirror, and the adjusting mechanism is used to adjust the zeroing stripe and translation of the optical element under test relative to the standard reference mirror.

Images