Large-aperture mirror surface shape high-precision detection method and device

Abstract

A large aperture mirror surface shape high precision detection method and device, which removes the surface shape error caused by the limited accuracy of the reference surface when using the sub-aperture stitching method to detect a single sub-aperture, improves the detection accuracy, extends the absolute detection technology of the double shear translation method to the large aperture mirror detection field, expands the mirror size that can be measured, and reduces the adjustment difficulty in the process of detecting the large aperture mirror. It comprises: (1) building a measuring device; (2) detecting each sub-aperture area five times; (3) moving the measured mirror, so that the outgoing beam of the interferometer covers other undetected sub-aperture areas in turn, and all sub-aperture areas are subjected to step (2); (4) repeating step (3) until all sub-apertures are detected; (5) using the structure method based on discrete phase data, the surface shape of each sub-aperture is restored according to the differential surface shape data of each sub-aperture; (6) the full aperture surface shape of the measured mirror is obtained by splicing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectric measurement, and particularly relates to a large-aperture mirror surface shape high-precision detection method and a large-aperture mirror surface shape high-precision detection device, and the large-aperture mirror mainly refers to a large-aperture plane mirror. BACKGROUND

[0002] With the development of science and technology, the large-aperture plane mirror is applied more and more widely in the frontiers such as space optics, astronomical optics and ground-based space target detection, and therefore the requirements for the surface shape machining and manufacturing precision of the large-aperture plane mirror are higher and higher, and the requirements for the precision of the surface shape detection technology are also improved, even reaching the nanometer level.

[0003] The existing methods for detecting the large-aperture plane mirror include using a large-aperture phase-shifting interferometer, the Ritchey-Common method, the five-prism scanning method and the sub-aperture stitching method. The large-aperture interferometer needs a large-aperture high-precision reference mirror, and such a reference mirror has a large machining difficulty, a long manufacturing cycle and a high cost, and therefore the method is limited in application. The Ritchey-Common method is limited in the size of the optical element that can be detected by a standard spherical mirror, and therefore the size of the plane mirror that can be detected is usually less than 1 m. If a larger size plane mirror is detected, a larger size standard spherical mirror is needed, which has a high manufacturing cost, and therefore the application of the Ritchey-Common method is limited. The five-prism scanning method uses a point scanning measuring instrument, and only one-dimensional data can be obtained each time, and the low-frequency information of the surface shape can be obtained after stitching. The five-prism scanning method has a low measurement efficiency and a limitation in obtaining high-frequency information, and therefore the application of the five-prism scanning method is limited. The sub-aperture stitching method divides the measured element into multiple sub-apertures that overlap with each other, and the interferometer is used to detect each sub-aperture, and then the full-aperture surface shape information of the measured element is obtained by stitching. However, the traditional sub-aperture stitching method is a relative measurement method, and the measurement precision is limited by the machining precision of the reference surface. When a single sub-aperture is detected, the surface shape error of the reference surface is introduced into the detection result due to the limited surface shape precision of the reference mirror, and therefore the final detection precision is affected.

[0004] The four methods above are all relative measurement methods relying on reference surface, and the measurement accuracy is limited by the machining accuracy of the reference mirror. In contrast, the absolute detection technology is a detection technology that eliminates the influence of system errors mainly caused by the reference surface in the detection process, thereby obtaining the absolute surface shape information of the measured element. At present, the methods for absolute detection of plane mirrors mainly include three mutual detection methods, rotation method, liquid surface reference method and translation difference method. Among them, the three mutual detection method and its many extension methods all need three optical elements, and replacement, flipping and other operations are needed in the detection process, which is easy to introduce installation and adjustment errors. The rotation method needs to rotate the measured element several times, which is easy to introduce rotation error and eccentric error, and this method is not suitable for non-circular optical elements. The stability of the liquid surface in the liquid surface reference method is easily disturbed by the environment and system equipment, and the laboratory conditions need to be strictly controlled during the detection process, so it is difficult to popularize in actual detection. The translation difference method only needs to translate the optical element in a small range during the detection process, and the operation is relatively simple. In the traditional translation method, the translation amount is generally the spatial distance corresponding to one pixel, so the signal-to-noise ratio is low, and the double shear translation method uses two large translation amounts in two directions for translation, which can improve the signal-to-noise ratio while ensuring high lateral resolution. However, when using the above absolute detection technology to detect the plane mirror, a reference mirror with the same size or even larger than the measured mirror is needed, and for large-aperture measured mirrors, such reference mirrors have long manufacturing cycle and high cost, so the absolute detection technology is less used in the field of large-aperture plane mirror detection.

[0005] At present, the difficulty in detecting large-aperture plane mirrors is the lack of a large-aperture plane mirror surface shape high-precision detection method with high detection accuracy and convenient installation and adjustment during detection. SUMMARY

[0006] To overcome the defects of the prior art, the technical problem to be solved by the present application is to provide a large-aperture mirror surface shape high-precision detection method which not only eliminates the reference surface shape error introduced by the limitation of the reference surface when using the sub-aperture stitching method to detect a single sub-aperture, thereby improving the detection accuracy, but also extends the double shear translation method, an absolute detection technology, to the field of large-aperture plane mirror detection, thereby reducing the installation and adjustment difficulty in the detection process of large-aperture plane mirrors and expanding the mirror size that can be measured by the absolute detection technology.

[0007] The technical scheme of the present application is: a large-aperture mirror surface shape high-precision detection method, comprising the following steps:

[0008] (1) Building a measurement device: fixing the measured mirror on the translation device, adjusting the relative position of the interferometer and the measured mirror, so that the centers of the interferometer and the measured mirror are on the same horizontal line, and the light beam emitted from the interferometer covers the central sub-aperture area of the measured mirror;

[0009] (2) Let the direction of the optical axis of the interferometer be the z-axis, first perform a detection, and the result is recorded as φ(x, y). The translation device is used to translate the measured mirror in the positive direction of the x-axis and the y-axis twice, the translation amount of single direction twice is s1 pixels and s2 pixels corresponding to the spatial distance, and s1 and s2 are co-prime, after each translation, a detection is performed, and the detection results of four positions are obtained, which are recorded as φ(x+s1, y), φ(x+s2, y), φ(x, y+s1), and φ(x, y+s2);

[0010]

[0011] (3) Move the measured mirror, so that the light beams emitted from the interferometer cover other undetected sub-aperture regions in turn, and perform five detections of step (2) for each sub-aperture region;

[0012] (4) Repeat step (3) until all sub-aperture regions are detected;

[0013] (5) Subtract the detection results after translation from the detection results before translation to obtain the differential surface shape data of each sub-aperture of the measured mirror, and use the structure method based on discrete phase data to restore the surface shape of each sub-aperture of the measured mirror according to the differential surface shape data of each sub-aperture;

[0014] (6) Splice the restored sub-aperture surface shape data to obtain the full-aperture surface shape of the measured mirror.

[0015] The application combines the absolute detection technology and the sub-aperture splicing method, divides the large-aperture plane measured mirror into n sub-apertures, uses the detection device of the sub-aperture splicing method, and uses the double shear translation method to perform absolute detection on each sub-aperture region on the measured surface and then splices to obtain the full-aperture surface shape of the measured mirror, so that not only the reference surface shape error introduced when detecting a single sub-aperture using the traditional sub-aperture splicing method is removed, the surface shape detection precision is improved, but also the absolute detection technology is applied to the large-aperture plane mirror, and the application range of the absolute detection technology is expanded.

[0016] A large-aperture mirror surface shape high-precision detection device is also provided, which comprises a sub-aperture measurement module, a sub-aperture absolute surface shape reconstruction module, and a full-aperture surface shape splicing module.

[0017] The sub-aperture measurement module measures all sub-apertures divided on the measured surface. When measuring a sub-aperture, five relative measurements are performed at five positions, i.e., the original position, after x-axis positive direction translation by s1 pixels, after x-axis positive direction translation by s2 pixels, after y-axis positive direction translation by s1 pixels, and after y-axis positive direction translation by s2 pixels.

[0018] ​The sub-aperture absolute surface shape reconstruction module reconstructs the absolute surface shape of the measured sub-aperture by using the algorithm of the double-shearing translation method and the measurement results of the measured sub-aperture at five positions obtained by the sub-aperture measurement module.

[0019] The full-aperture surface shape splicing module splices the absolute surface shapes of the sub-apertures to obtain the absolute surface shape of the full-aperture of the measured mirror by using a sub-aperture splicing algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a flowchart of the large-aperture mirror surface shape high-precision detection method according to the present application.

[0021] Figure 2 is a schematic diagram of the measurement device according to the present application. Wherein, 1-optical platform, 2-interferometer support table, 3-interferometer, 4-reference mirror, 5-large-aperture measured mirror, 6-translation device.

[0022] Figure 3 is a schematic diagram of a division mode of dividing a rectangular plane mirror into multiple sub-apertures in an embodiment of the large-aperture mirror surface shape high-precision detection method according to the present application. Wherein, 501, 502, …, 5n represent n sub-apertures of the measured mirror, and 5n is the nth sub-aperture. There is an overlapping area between adjacent sub-apertures.

[0023] Figure 4 is a flowchart of detecting the surface shape data of each sub-aperture by using the double-shearing translation method in an embodiment of the large-aperture mirror surface shape high-precision detection method according to the present application. DETAILED DESCRIPTION

[0024] As shown in Figure 1 , a large-aperture mirror surface shape high-precision detection method comprises the following steps:

[0025] (1) Build a measurement device: fix the measured mirror on the translation device, adjust the relative position of the interferometer and the measured mirror, so that the center of the interferometer and the measured mirror are on the same horizontal line, and the light beam emitted from the interferometer covers the central sub-aperture area of the measured mirror;

[0026] (2) Let the direction of the optical axis of the interferometer be the z-axis, first perform a detection, and the result is recorded as

[0027] φ(x,y), use the translation device to translate the measured mirror in the positive direction of the x-axis and the y-axis twice, and the translation amount of single-direction twice translation is the space distance corresponding to s1 pixels and s2 pixels, and s1 and s2 are coprime. After each translation, a detection is performed

[0028] , four detection results at four positions are obtained, which are recorded as φ(x+s1,y),

[0029] φ(x+s2,y), φ(x,y+s1), φ(x,y+s2);

[0030] (3) moving the measured mirror to make the light beams out of the interferometer cover other undetected sub-aperture regions in turn, and performing the five detections of step (2) for each sub-aperture region;

[0031] (4) repeating step (3) until all sub-apertures are detected;

[0032] (5) subtracting the detection results after the translation of each sub-aperture from the detection results before the translation to obtain differential surface shape data of each sub-aperture of the measured mirror, and using a structure method based on discrete phase data to restore the surface shape of each sub-aperture of the measured mirror according to the differential surface shape data of each sub-aperture;

[0033] (6) splicing the restored surface shape data of each sub-aperture to obtain the full-aperture surface shape of the measured mirror.

[0034] The present application divides a large-aperture plane measured mirror into n sub-apertures by combining the absolute detection technology with the sub-aperture splicing method, uses a detection device of the sub-aperture splicing method, and uses the double-shearing translation method to perform absolute detection on each sub-aperture region on the measured surface and then splices to obtain the full-aperture surface shape of the measured mirror, so that not only the reference surface surface shape error introduced when detecting a single sub-aperture using the traditional sub-aperture splicing method is removed, but also the surface shape detection precision is improved, and the absolute detection technology is applied to the large-aperture plane mirror, thereby expanding the application range of the absolute detection technology.

[0035] Preferably, in step (1), the measuring device adopts a horizontal structure and is arranged on an optical platform, the measured mirror is fixed on a mirror frame of a translation device, and the translation device is used to move the measured mirror when measuring different positions of a single sub-aperture and when measuring different sub-apertures.

[0036] Preferably, in step (1), when the measured mirror is a large-aperture rectangular plane mirror, the measured mirror is divided into multiple sub-apertures, and each sub-aperture has the same shape and size. Figure 3 As shown in FIG. 1, the measured mirror 5 is divided into nine sub-apertures 501-509, and each sub-aperture 501-509 has the same shape and size.

[0037] Preferably, in step (3), s1 is taken as a spatial distance corresponding to 11 pixels, and s2 is taken as a spatial distance corresponding to 18 pixels. The spatial distance corresponding to each pixel can be calculated according to the actual used interferometer aperture and resolution.

[0038] Preferably, in the step (5), the differential surface data of the measured mirror aperture along the x direction and the y direction is x (x,y), Δφ y (x,y) is formula (1):

[0039]

[0040] The relationship of the differential surface and the recovered surface φ used is:

[0041]

[0042] Where, Y x , Y y is the Jacobian matrix, Specifically represented as:

[0043]

[0044] Where,

[0045]

[0046] Synthesizing formulas (2)-(4), we have:

[0047] Δφ=Yφ (5)

[0048] The absolute surface of the measured mirror is obtained by solving formula (5) by the least square method.

[0049] A large-aperture mirror surface high-precision detection device is also provided, which comprises a sub-aperture measurement module, a sub-aperture absolute surface reconstruction module, and a full-aperture surface splicing module.

[0050] The sub-aperture measurement module measures all sub-apertures divided by the measured surface. When measuring a certain sub-aperture, five relative measurements are performed at five positions, i.e., the original position, after shifting s1 pixels in the positive direction of the x axis, after shifting s2 pixels in the positive direction of the x axis, after shifting s1 pixels in the positive direction of the y axis, and after shifting s2 pixels in the positive direction of the y axis. The sub-aperture absolute surface reconstruction module reconstructs the absolute surface of the measured sub-aperture by using the algorithm of the double-shearing translation method and the measurement results of the measured sub-aperture at the five positions obtained by the sub-aperture measurement module.

[0051] The full-aperture surface splicing module splices the absolute surfaces of the sub-apertures to obtain the absolute surface of the full-aperture of the measured mirror by using the sub-aperture splicing algorithm.

[0052] Preferably, as Figure 2As shown, the device uses equipment including: an optical platform 1, an interferometer support table 2, an interferometer 3, a reference mirror 4, a measured mirror 5, and a translation device 6. The interferometer support table and the translation device are placed on the optical platform, the interferometer is placed on the interferometer support table, the measured mirror is fixed on the translation device, the relative positions of the interferometer and the measured mirror are adjusted so that the centers of the interferometer and the measured mirror are on the same horizontal line, and the light beam emitted from the interferometer covers the central sub-aperture region of the measured mirror.

[0053] The following detailed description of the application is based on one specific embodiment.

[0054] The measured mirror in the embodiment is a rectangular plane mirror with a size of 100*70 mm, the reference plane mirror of the interferometer is 50.8 mm, and the working wavelength is 632.8 nm. The sub-aperture region on the measured mirror irradiated by the light beam emitted from the interferometer is circular with a diameter of 50.8 mm. The specific implementation steps are as follows:

[0055] Step one: the relative positions of the interferometer and the measured mirror are adjusted so that the centers of the interferometer and the measured mirror are on the same horizontal line, and the light beam emitted from the interferometer covers the central sub-aperture of the measured mirror and the captured fringe image of the interferometer meets the requirements of interference detection.

[0056] Step two: the central sub-aperture region is detected for the first time using the interferometer, the detection result is saved, then the measured mirror is translated by 11 pixels along the x-axis direction using the translation device, the second detection is performed, the detection result is saved, the measured mirror is translated by 18 pixels along the x-axis direction, the third detection is performed, and the detection result is saved.

[0057] Step three: after the translation and detection along the x-axis direction are completed twice, the measured mirror is translated back to the original position.

[0058] Step four: the measured mirror is translated by 11 pixels along the y-axis direction using the translation device, the fourth detection is performed, the detection result is saved, the measured mirror is translated by 18 pixels along the y-axis direction using the translation device, the fifth detection is performed, and the detection result is saved.

[0059] Step five: after the detection of the central sub-aperture is completed, the measured mirror is moved so that the light beam emitted from the interferometer covers other undetected sub-aperture regions in turn, and steps two to four are repeated to complete five detections for a total of nine sub-aperture regions.

[0060] Step six: the detection result of each sub-aperture region after translation is subtracted from the detection result before translation to obtain the differential surface shape data of each sub-aperture, the structure method based on discrete phase data is used for reconstruction to obtain the absolute surface shape of each sub-aperture.

[0061] Step seven: the absolute surface shape data of the nine sub-apertures are spliced to obtain the full-aperture surface shape of the measured mirror.

[0062] The above steps are integrated, and high-precision detection of a large-aperture plane mirror surface shape can be realized.

[0063] The beneficial effects of the present application are as follows:

[0064] 1. The reference surface shape error introduced when using the traditional sub-aperture stitching method to detect the sub-aperture is removed in the measurement process, and the surface shape detection precision is improved.

[0065] 2. The absolute detection technology is applied to a large-aperture plane mirror, the adjustment difficulty in the detection process of the large-aperture plane mirror is reduced, and the mirror size that can be measured by the absolute detection technology is expanded.

[0066] The double-shearing translation method, which is an absolute detection technology, is further extended to the field of large-aperture plane mirror detection, and the application range of the absolute detection technology is expanded.

[0067] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Any simple modification, equivalent change and modification made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A high-precision detection method for the surface shape of a large-aperture mirror, characterized in that: It includes the following steps: (1) Set up the measuring device: Fix the mirror to be measured on the translation device, adjust the relative position of the interferometer and the mirror to be measured so that the center of the interferometer and the mirror to be measured are on the same horizontal line, and the beam emitted from the interferometer covers the central sub-aperture area of ​​the mirror to be measured. (2) Let the direction of the interferometer's optical axis be the z-axis. First, perform a detection and record the result as φ(x,y). Use the translation device to translate the mirror under test twice in the positive x-axis and y-axis directions. The translation amount of the two translations in a single direction is the spatial distance corresponding to s1 pixels and s2 pixels, respectively. S1 and S2 are coprime. Perform a detection after each translation to obtain the detection results at four positions, which are recorded as φ(x+s1,y), φ(x+s2,y), φ(x,y+s1), and φ(x,y+s2). (3) Move the mirror under test so that the beam emitted from the interferometer sequentially covers other undetected sub-aperture regions, and perform five tests in step (2) on each sub-aperture region. (4) Repeat step (3) until all sub-apertures have been detected; (5) Subtract the detection results after each sub-aperture is translated from the detection results before translation to obtain the differential surface shape data of each sub-aperture of the test mirror. Using the structure method based on discrete phase data, the surface shape of each sub-aperture of the test mirror is restored according to the differential surface shape data of each sub-aperture. (6) The restored sub-aperture surface data are spliced ​​together to obtain the full aperture surface of the mirror under test.

2. The high-precision detection method for the surface shape of a large-aperture mirror according to claim 1, characterized in that: In step (1), the measuring device adopts a horizontal structure and is arranged on an optical platform. The mirror under test is fixed on the mirror frame of the translation device. When measuring a single sub-aperture at different positions and when measuring different sub-apertures, the mirror under test is moved by the translation device.

3. The high-precision detection method for the surface shape of a large-aperture mirror according to claim 2, characterized in that: In step (1), when the mirror under test is a large-aperture rectangular plane mirror, the mirror under test is divided into multiple sub-apertures, and each sub-aperture has the same shape and size.

4. The high-precision detection method for the surface shape of a large-aperture mirror according to claim 3, characterized in that: In step (3), s1 is taken as the spatial distance corresponding to 11 pixels and s2 is taken as the spatial distance corresponding to 18 pixels.

5. A high-precision detection device for the surface shape of a large-aperture mirror, used to implement the high-precision detection method for the surface shape of a large-aperture mirror according to any one of claims 1-4, characterized in that: It includes: Sub-aperture measurement module, sub-aperture absolute surface shape reconstruction module, full-aperture surface shape splicing module; The sub-aperture measurement module measures all sub-apertures divided into the surface being measured. When measuring a certain sub-aperture, it performs five relative measurements at five positions: the original position, after shifting s1 pixels in the positive x-axis direction, after shifting s2 pixels in the positive x-axis direction, after shifting s1 pixels in the positive y-axis direction, and after shifting s2 pixels in the positive y-axis direction. The sub-aperture absolute surface shape reconstruction module reconstructs the absolute surface shape of the sub-aperture by using the double shear translation algorithm and the measurement results of the sub-aperture at five positions obtained by the sub-aperture measurement module. The full-aperture surface shape stitching module uses a sub-aperture stitching algorithm to stitch together the absolute surface shapes of each sub-aperture to obtain the absolute surface shape of the full aperture of the mirror under test.

6. The high-precision detection device for large-aperture mirror surface shape according to claim 5, characterized in that: The equipment used in this device includes: an optical platform (1), an interferometer support stage (2), an interferometer (3), a reference mirror (4), a mirror under test (5), and a translation device (6). The interferometer support stage and the translation device are placed on the optical platform, the interferometer is placed on the interferometer support stage, and the mirror under test is fixed on the translation device. Initially, the relative positions of the interferometer and the mirror under test are adjusted so that the centers of the interferometer and the mirror under test are on the same horizontal line, and the beam emitted from the interferometer covers the central sub-aperture region of the mirror under test.

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