Two-dimensional optical scanning surface shape detection device and method

Abstract

The invention provides a two-dimensional optical scanning surface shape detection device, which is used for measuring the three-dimensional surface shape of a reflector to be measured, the shape of the reflector to be measured comprises a plane, a spherical surface and a cylindrical surface, and the detection device comprises a measurement light detection system, an optical scanning system and an optical scanning system, the device comprises a laser, a collimating lens, a two-dimensional array structure pi phase plate and a first beam splitter prism which are sequentially arranged on a first optical axis along the direction of an optical path, and a first reflector, a second lens and a first detector which are sequentially arranged on a second optical axis; the reference light measuring system comprises a sliding positioning part and a fixed positioning part which are separated from each other, and is used for acquiring angle deviation information between the sliding positioning part and the fixed positioning part; and the scanning system comprises a guide rail sliding table, and a measuring light detection system and a sliding positioning part are mounted on the guide rail sliding table. According to the detection device disclosed by the invention, the far-field cross dark line array is generated by utilizing the two-dimensional array structure pi phase plate, so that two-dimensional information of the surface of the reflector to be detected is obtained, and high-precision two-dimensional scanning measurement is realized.

Description

Technical Field

[0001] The present invention belongs to the field of optical detection, and relates to a two-dimensional optical scanning surface shape detection device and method, which is applicable to the surface shape detection of planes, spherical surfaces, cylindrical surfaces, etc. The advantage is that non-contact two-dimensional scanning is used to achieve high-precision and large-size detection. Background Art

[0002] As Figure 1 shown is a two-dimensional long-range surface shape detection device and detection method disclosed in a Chinese patent document with a patent publication number of CN106840030B in a prior application. The detection device mainly consists of a semiconductor laser 1, a two-dimensional array structure π-phase plate 2, a second beam splitting prism 3, a pentagonal prism 4, a lens 5, right-angled prisms 6-10, and a CCD detector 11. Its principle is that the collimated laser beam emitted by the semiconductor laser 1 irradiates on the two-dimensional array structure π-phase plate 2, and its far-field light intensity distribution is a light spot with a cross-shaped dark line at the center; after the beam passes through the second beam splitting prism 3, one of the beams irradiates on the pentagonal prism 4 installed on the moving guide rail, and after being refracted by the pentagonal prism 4, it irradiates on the mirror surface of the to-be-tested mirror 12. After being reflected by the to-be-tested mirror 12, the beam is refracted again by the pentagonal prism 4 and then irradiates on the second beam splitting prism 3. After passing through the lens 5, it reaches the CCD detector 11 after multiple refractions by the right-angled prisms 6-10. When the guide rail scans and measures along the to-be-tested surface, the measurement light spot continuously moves on the CCD detector 11. The amount of movement on the CCD detector 11 is measured, multiplied by the calibrated coefficient, to obtain the slope distribution of the to-be-tested surface, and then the height distribution of the to-be-tested surface is obtained through integration.

[0003] The disadvantages of the above two-dimensional long-range surface shape detection device and detection method are as follows:

[0004] 1) The two-dimensional array structure π-phase plate 2 therein is used to generate a two-dimensional diffraction array, and the projection of the diffraction array can be used to locate the measurement light spot. However, due to diffraction, when the etching unit width of the phase array plate, that is, as Figure 2A shown, when the lateral (sagittal) resolution ≥ 2 mm, the imaging is clear and a series of light spot centroid coordinates can be accurately calculated. But as Figure 2B shown, when the lateral resolution ≤ 1 mm, the array light spots will undergo diffraction superposition, and deviation will occur when calculating the centroid coordinates. The detection result with an array phase plate resolution of 2 mm can be applied to the detection and processing of high-precision optical components in the X-band. However, with the development of advanced light sources, the requirements for the intermediate-frequency structure of X-band optical components are getting higher and higher. Therefore, higher requirements are put forward for the lateral resolution of processing and detection, and a two-dimensional detection method with a lateral resolution better than 1 mm is urgently needed.

[0005] 2) The above two-dimensional long-range surface shape detection device and detection method adopt a scanning detection method. There is only one pentaprism on the scanning head, and the structure is simple. However, when scanning a large reflective surface, the width of the scanning light spot will exceed the linear region of the lens and no longer satisfy the paraxial approximation, resulting in slight changes in the imaging of the light spot at different measurement positions due to defocus. The distortion of the imaging light spot when scanning and measuring a plane mirror with a length of 520 mm at measurement positions of 10 mm, 260 mm, and 510 mm on the reflector is shown in Figure 3. These distortions will affect the accuracy of the light spot position calculation. And the lens needs to work in the linear region. When the broadening is too large, it will deviate from the linear region. Therefore, it is difficult to achieve large-range scanning measurement when detecting high-precision reflectors.

[0006] Therefore, there is an urgent need for a new two-dimensional long-range surface shape detection device and detection method to achieve higher lateral resolution and a larger scanning measurement range. Summary of the Invention

[0007] The purpose of the present invention is to provide a two-dimensional optical scanning surface shape detection device and method to achieve high-precision two-dimensional scanning measurement.

[0008] To achieve the above purpose, the present invention provides a two-dimensional optical scanning surface shape detection device for measuring a to-be-measured reflector, including: a measurement light detection system, which includes a laser, a collimating lens, a two-dimensional array structure π-phase plate, and a first beam splitter prism arranged in sequence along the optical path on a first optical axis, and a first reflector, a second lens, and a first detector arranged in sequence on a second optical axis; a reference light measurement system, which includes a sliding positioning part and a fixed positioning part spaced apart, configured to obtain the angular offset information between the sliding positioning part and the fixed positioning part; and a scanning system, which includes a guide rail slider, on which the measurement light detection system and the sliding positioning part are installed.

[0009] The sliding positioning part of the reference light measurement system includes a second beam splitter prism, a third lens, and a second detector arranged in sequence on a third optical axis, and the fixed positioning part of the reference light measurement system includes a second reflector fixed relative to the ground;

[0010] Alternatively, the sliding positioning part of the reference light measurement system includes the first reflector, the second lens, and the first detector, and the fixed positioning part of the reference light measurement system includes a second reflector fixed relative to the ground.

[0011] The first reflector is configured to reflect the light from the first beam splitter prism to the second lens; the first beam splitter prism is configured to split the light from the two-dimensional array structure π-phase plate to be respectively transmitted to the second reflector and the to-be-measured reflector, and is configured to reflect the light from the to-be-measured reflector to the first reflector.

[0012] The sliding positioning part of the reference light measurement system includes a third reflecting mirror, and the fixed positioning part of the reference light measurement system includes an autocollimator fixed relative to the ground.

[0013] The to-be-tested reflecting mirror is arranged downstream of the first beam splitting prism on the first optical axis and is fixed relative to the ground; and the fixed positioning part is fixed relative to the ground; the shape of the to-be-tested reflecting mirror includes a plane, a spherical surface, and a cylindrical surface.

[0014] The scanning system further includes a scanning guide rail, the scanning guide rail adopts a high-precision air-floating guide rail or a mechanical guide rail, and the guide rail slide is installed on the scanning guide rail.

[0015] The two-dimensional array structure π-phase plate is in a linear shape or a cross shape, and the number of etching units of the two-dimensional array structure π-phase plate makes the total etching width greater than the total width of the to-be-tested reflecting mirror.

[0016] The two-dimensional array structure π-phase plate adopts a two-dimensional array structure π-phase plate with a dislocation structure, and the two sets of diffracted cross dark lines formed by it are staggered to improve the lateral measurement resolution.

[0017] On the other hand, the present invention provides a two-dimensional optical scanning surface shape detection method, including:

[0018] S1: Provide the two-dimensional optical scanning surface shape detection device described above, and install the to-be-tested reflecting mirror in place to start the measurement;

[0019] S2: When the measurement light moves with the guide rail slide and irradiates each position of the to-be-tested reflecting mirror, use the measurement light detection system to record the offset of the measurement light spot at this position; use the reference light measurement system to simultaneously record the offset of the reference light spot at this position or the deflection angle of the reference light;

[0020] S3: Determine the height distribution of the to-be-tested surface according to the offset of the measurement light spot and the offset of the reference light spot.

[0021] The specific steps of step S3 include:

[0022] S31: Subtract the offset corresponding to the deflection angle of the reference light spot or the reference light from the offset of the measurement light spot as the true offset of each position of the to-be-tested reflecting mirror, and convert according to the true offset of each position of the to-be-tested reflecting mirror multiplied by the slope coefficient to obtain the slope distribution of the to-be-tested reflecting mirror;

[0023] S32: Integrate according to the slope distribution of the to-be-tested reflecting mirror to obtain the height distribution of the measured surface.

[0024] The two-dimensional optical scanning surface shape detection device of the present invention uses a two-dimensional array structure π-phase plate to generate a far-field cross dark line array, obtains two-dimensional information of the surface of the mirror to be measured, and realizes high-precision two-dimensional scanning measurement. The dark line has little correlation with the intensity of the light source. Therefore, the intensity drift of the laser light source and disturbances such as dust in the optical path have no influence on the detection result; and a reference light measurement system is adopted, which can effectively counter the influence of environmental vibration, etc., and can obtain high-precision measurement results in both the meridional and sagittal directions at the same time, and is not sensitive to environmental vibration. The measurement accuracy of the system is little affected by environmental vibration, can suppress the influence of environmental air flow and temperature drift, and does not require high-precision reference optical elements or high-precision reference wavefronts.

[0025] In a traditional long-range surface profiler, the size of the scanned light spot is usually <1 mm, that is, the measurement width on the surface to be measured is <1 mm. For the two-dimensional scanning structure of the present invention, as long as the number of etched units of the phase plate is sufficient to make the total etched width greater than the surface to be measured, the array light spots generated by diffraction can cover the entire width of the surface to be measured in one scan measurement. In the application of the present invention, a large-range measurement of a 500 mm × 40 mm surface to be measured can already be completed, quickly realizing high-precision two-dimensional scanning measurement of large-size high-precision optical elements, and obtaining two-dimensional slope distribution and height distribution information of the surface to be measured.

[0026] Furthermore, the two sets of diffraction cross dark lines formed by the misaligned array phase plate adopted in the present invention are staggered, and the calculated spot coordinate resolution is 1 / 2 of that of a symmetric phase plate with the same etched width. Therefore, the lateral measurement resolution can be improved. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of a two-dimensional long-range surface shape detection device disclosed in a Chinese patent document with a patent publication number of CN106840030B in a prior application.

[0028] Figures 2A - 2D is a structural diagram of an array phase plate with different lateral resolutions of the two-dimensional long-range surface shape detection device and the corresponding imaging spot diagram; Figure 2A and Figure 2B are respectively a structural diagram of an array phase plate with a lateral resolution of 2 mm and a clear imaging spot diagram, Figure 2C and Figure 2D are respectively a structural diagram of an array phase plate with a lateral resolution of 1 mm and an imaging spot diagram of diffraction superposition.

[0029] Figures 3A - 3C is a distortion diagram of the imaging array spots at different measurement positions on a 520 mm plane mirror, where, Figure 3A is an imaging spot diagram at a measurement position of 10 mm, Figure 3B is an imaging spot diagram at a measurement position of 260 mm, Figure 3CIt is an image of the imaging light spot at the measurement position of 510 mm.

[0030] Figure 4 It is an optical path diagram of the two-dimensional optical scanning surface shape detection device according to the first embodiment of the present invention.

[0031] Figure 5 It is an optical path diagram of the two-dimensional optical scanning surface shape detection device according to the second embodiment of the present invention.

[0032] Figure 6A and Figure 6B It is a structural diagram and a diffraction simulation diagram of a two-dimensional array structure π-phase plate;

[0033] Figure 7A and Figure 7B It is an experimental result diagram of the present invention, where 7A is a scanning mode diagram of the two-dimensional optical scanning surface shape detection device, Figure 7B It is an image of the height distribution of the measured mirror to be measured. Specific embodiments

[0034] The following combines the accompanying drawings to give a preferred embodiment of the present invention and describes it in detail to better understand the functions and features of the present invention.

[0035] The working principle of the two-dimensional optical scanning surface shape detection device of the present invention is as follows: The two-dimensional optical scanning surface shape detection device is an f-θ laser scanning measurement system based on a two-dimensional array structure π-phase plate, which mainly consists of a scanning guide rail, a laser, a two-dimensional array structure π-phase plate, a beam splitter prism, a second lens, and a first detector. The principle is that the laser beam emitted by the laser is collimated and expanded into parallel light by a collimating lens and then irradiated onto the two-dimensional array structure π-phase plate, and its far-field light intensity distribution is a spot array with a cross-shaped dark line in the center; after this beam passes through the first beam splitter prism, one of the beams is irradiated onto the mirror to be measured, and after being reflected by the mirror to be measured, it is turned by the first mirror and converges onto the first detector through the second lens to obtain a measurement light spot. Another beam of light emitted by the first beam splitter prism or by the autocollimator is reflected by the second mirror or the third mirror and then collected by the target surface of the second detector or the autocollimator to obtain a reference light spot.

[0036] The shapes of the mirrors to be measured include planes, spherical surfaces, cylindrical surfaces, etc. When the scanning guide rail scans and measures the mirror to be measured, due to the minute height fluctuations on the mirror surface of the mirror to be measured, the measurement light spot will thus have minute angular changes, and the measurement light spot will have minute displacements. By measuring the offset of the measurement light spot and subtracting the offset of the reference light spot (which reflects the pitch / yaw angle errors of the guide rail slider at each measurement position), the true offset of each position of the mirror to be measured can be obtained, and then the slope distribution of the mirror to be measured can be obtained. By integration, the height distribution of the mirror to be measured can be obtained.

[0037] First Embodiment: Two-Dimensional Optical Scanning Surface Shape Detection Device

[0038] Figure 4 It is an optical path diagram of a two-dimensional optical scanning surface shape detection device according to the first embodiment of the present invention.

[0039] As Figure 4 shown, the two-dimensional optical scanning surface shape detection device is a two-dimensional optical scanning surface shape detection device in a reference light mode, which includes a laser 103, a collimating lens 104, a two-dimensional array structure π-phase plate 105, a first beam splitter prism 106, and a to-be-measured reflector 113 arranged in sequence along the optical path on the first optical axis, a first reflector 107, a second lens 108, and a first detector 109 arranged in sequence on the second optical axis, and a second beam splitter prism 110, a third lens 111, and a second detector 112 arranged in sequence on the third optical axis. The first reflector 107, the first beam splitter prism 106, and the second beam splitter prism 110 are located on the fourth optical axis with a second reflector 114.

[0040] The first reflector 107 is arranged to reflect the light on the fourth optical axis to the second lens 108. The first beam splitter prism 106 is arranged to split the light from the two-dimensional array structure π-phase plate 105 to be respectively transmitted to the second reflector 114 and the to-be-measured reflector 113, and is arranged to reflect the light from the to-be-measured reflector 113 to the first reflector 107. The second beam splitter prism 110 is arranged to allow the light from the first beam splitter prism 106 to pass through and reflect the light from the second reflector 114 to the third lens 111. Thus, the laser 103, the collimating lens 104, the two-dimensional array structure π-phase plate 105, the first beam splitter prism 106, the first reflector 107, the second lens 108, and the first detector 109 form a measurement light detection system, which uses the two-dimensional array structure π-phase plate to detect the displacement information of the measurement light beam. The second reflector 114, the second beam splitter prism 110, the third lens 111, and the second detector 112 form a reference light measurement system.

[0041] In this embodiment, the first optical axis, the second optical axis, and the third optical axis are parallel to each other, and the fourth optical axis is perpendicular to the first optical axis.

[0042] The described measurement light detection system, as well as the second beam splitter prism 110, the third lens 111, and the second detector 112 (as the sliding positioning part of the reference light measurement system) of the reference light measurement system, are all installed on the guide rail slider 102 that can slide on the scanning guide rail 101, and can move and scan together with the guide rail slider 102. The scanning guide rail 101 and the guide rail slider 102 form a scanning system. The mirror 113 to be measured is the measurement object and is fixed relative to the ground. The second mirror 114 of the reference light measurement system, as the reflection component of the reference beam (i.e., as the fixed positioning part of the reference light measurement system), is fixed on the mounting bracket outside the scanning guide rail 101 to be fixed relative to the ground. The reference light measurement system is set to obtain the angular offset information between the sliding positioning part and the fixed positioning part.

[0043] In this embodiment, the reference light used by the measurement light detection system can directly use a laser beam, and the collimation is achieved by measuring the spot imaging position of the measurement beam on the detector 112.

[0044] Among them, the laser 103 is a semiconductor laser, and the collimating lens 104 is an f-θ type lens optimized for the specific wavelength of the semiconductor laser 103.

[0045] The scanning guide rail 101 can adopt a high-precision air-bearing guide rail or an ordinary mechanical guide rail.

[0046] In this embodiment, the two-dimensional array structure π-phase plate 105 can adjust the lateral resolution of the system by changing the size of the etched units arranged in the array to meet the requirements of different measurement occasions. The size of the etched units is determined by the required lateral resolution for measurement and ranges from 1 mm to 3 mm. In other embodiments, by replacing the two-dimensional array structure π-phase plate 105 with a one-dimensional cross structure phase plate or changing the software algorithm, high-precision one-dimensional scanning measurement can be achieved.

[0047] The working principle of the two-dimensional optical scanning surface shape detection device is as follows: (1) The thin beam emitted by the laser 103 is collimated and expanded into a wide parallel beam by the collimating lens 104 and then irradiated onto the two-dimensional array structure π-phase plate 105. The light intensity distribution of its far-field diffraction is a spot array with a cross-shaped dark line at the center. Different two-dimensional array structures result in spot arrays with different dark line distributions after diffraction. The clearer the dark line distribution, the higher the calculated spot positioning accuracy. After this beam passes through the first beam splitter prism 106, one of the beams is irradiated onto the mirror 113 to be measured, forming a measurement light beam. After being reflected by the mirror 113 to be measured, the measurement light beam enters the second lens 108 after being reflected by the first beam splitter prism 106 and the first mirror 107 and converges onto the target surface of the first detector 109, forming a measurement spot. (2) Another beam of light emitted by the first beam splitter prism 106 serves as a reference light beam. After being reflected by the second mirror 114, it is reflected by the second beam splitter prism 110 to turn by 90°, and finally converges onto the target surface of the second detector 112 by the third lens 111, forming a reference spot.

[0048] When the guide rail slider 102 scans different positions of the mirror 113 to be measured along a straight line, due to the slight height fluctuations on the mirror surface of the mirror 113 to be measured, the measurement light beam will generate a slight angular change, resulting in a slight displacement of the measurement spot on the target surface of the first detector 109. Measuring this displacement can obtain the surface shape information of the surface to be measured. The angular and deflection errors during the scanning movement of the guide rail slider 102 will also cause the measurement spot to displace on the target surface of the first detector 109, and these errors must be subtracted to obtain the accurate surface shape of the mirror 113 to be measured. Since the second mirror 114 is fixed outside the guide rail, the reference spot reflected on the target surface of the second detector 112 will also displace due to the movement errors of the guide rail slider 202. Measuring this displacement can obtain an independent movement error value.

[0049] Therefore, based on the two-dimensional optical scanning surface shape detection device described above, the implemented two-dimensional optical scanning surface shape detection method includes:

[0050] Step S1: Provide the two-dimensional optical scanning surface shape detection device described above, and install the mirror 113 to be measured in place to start the measurement;

[0051] Step S2: When the measurement light beam moves with the guide rail slider 102 and irradiates each position of the mirror 113 to be measured, use the first detector 109 of the measurement light detection system to record the offset of the measurement spot at this position; use the second detector 112 of the reference light measurement system to simultaneously record the offset of the reference spot at this position;

[0052] Among them, the positions of the measurement spot and the reference spot are respectively located at the centers of the detection areas of the first detector 109 and the second detector 112.

[0053] Step S3: Determine the height distribution of the surface to be measured based on the offset of the measurement light spot and the offset of the reference light spot.

[0054] The specific steps of Step S3 include:

[0055] Step S31: Subtract the offset of the reference light spot from the offset of the measurement light spot as the true offset of each position of the mirror 113 to be measured. Through conversion by multiplying the true offset of each position of the mirror 113 to be measured by the slope coefficient, the slope distribution of the mirror 113 to be measured is obtained. The calculation method of the slope coefficient can be referred to the specific implementation in paragraph

[0033] of the prior patent with publication number CN106840030B.

[0056] Step S32: Integrate according to the slope distribution of the mirror 113 to be measured to obtain the height distribution of the measured surface.

[0057] Thus, in the present invention, subtracting the offset of the measurement light spot from the offset of the reference light spot can obtain the true surface undulation of the surface to be measured, and then obtain the slope distribution of the surface to be measured. The height distribution of the surface to be measured can be calculated by integration.

[0058] In the present invention, the reference light measurement system can offset the influence of the tilt error of the guide rail movement on the measurement result. Therefore, in the present invention, the scanning guide rail 101 can adopt a high-precision air-floating guide rail or an ordinary mechanical guide rail.

[0059] In other embodiments, Figure 1 The shown reference light mode can be further simplified by removing the second beam splitter prism 110, the third lens 111, and the second detector 112. Therefore, the first beam splitter prism 106 is further arranged to allow the light from the second mirror 114 to pass through and propagate to the first mirror 107.

[0060] Thus, the horizontal light beam split by the first beam splitter prism 106 is reflected by the second mirror 114, passes through the first beam splitter prism 106, is reflected by the first mirror 107, and is converged by the second lens 108 onto the target surface of the first detector 109. The advantage of this mode is that the structure can be further simplified, but the second mirror 114 is arranged such that the reference light spot is located at the corner of the first detector 109. That is to say, the reference light spot is moved to the corner position of the first detector 109 by adjusting the tilt angle of the second mirror 114, while the measurement light spot is located at the center of the first detector 109. Therefore, the second mirror 114, the first mirror 107, the second lens 108, and the first detector 109 form a reference light measurement system. This requires a higher image processing algorithm.

[0061] Second Embodiment: Two-Dimensional Optical Scanning Surface Shape Detection Device

[0062] AsFigure 5 As shown, the two-dimensional optical scanning surface shape detection device is a two-dimensional optical scanning surface shape detection device in the autocollimator mode, which uses a commercial autocollimator to replace the reference light after beam splitting, and has the advantages of simpler structure and better integration.

[0063] As Figure 5 shown, the two-dimensional optical scanning surface shape detection device in the reference light mode includes a laser 203, a collimating lens 204, a two-dimensional array structure π-phase plate 205, a first beam splitting prism 206 and a to-be-measured reflecting mirror 211 arranged in sequence along the optical path on the first optical axis, a first reflecting mirror 207, a second lens 209 and a first detector 210 arranged in sequence on the second optical axis, and a third reflecting mirror 208 and an autocollimator 212.

[0064] The first reflecting mirror 207 is arranged to reflect the light from the first beam splitting prism 206 to the second lens 209, and the first beam splitting prism 206 is arranged to allow the light from the two-dimensional array structure π-phase plate 205 to pass through and reflect the light from the to-be-measured reflecting mirror 211 to the first reflecting mirror 207.

[0065] Thus, the laser 203, the collimating lens 204, the two-dimensional array structure π-phase plate 205, the first beam splitting prism 206, the first reflecting mirror 207, the second lens 209 and the first detector 210 form a measurement light detection system. The autocollimator 212 and the third reflecting mirror 208 form a reference light measurement system, where the third reflecting mirror 208 serves as the sliding positioning part of the reference light measurement system, and the autocollimator 212 serves as the fixed positioning part of the reference light measurement system. The reference light measurement system is arranged to obtain the angular offset information between the sliding positioning part and the fixed positioning part. In other embodiments, the reference light measurement system can use a commercial autocollimator or an autocollimation optical path as the reference light to measure the yaw of the guide rail while scanning the to-be-measured reflecting mirror.

[0066] The measurement light detection system and the third reflecting mirror 208 are both installed on the guide rail slider 202 of the scanning guide rail 201 and can move and scan together with the slider. The to-be-measured reflecting mirror 211 is the measurement object and is fixed relative to the ground. The autocollimator 212, as the light source and detection end of the reference beam, is fixed on the platform outside one end of the scanning guide rail 201 and is fixed relative to the ground.

[0067] The working principle of the two-dimensional optical scanning surface shape detection device is as follows: (1) The thin beam emitted by the laser 203 is collimated and expanded into a wide parallel beam by the collimating lens 204 and then irradiated onto the two-dimensional array structure π-phase plate 205. The light intensity distribution of its far-field diffraction is a spot array with a cross-shaped dark line at the center. After this beam passes through the first beam splitter prism 206, one of the beams is irradiated onto the mirror 211 to be measured, that is, the measurement light. After being reflected by the mirror 211 to be measured, the measurement light is deflected by the first beam splitter prism 206 and then reflected by the first mirror 207 and enters the second lens 209 and converges onto the target surface of the first detector 210 to form a measurement spot. (2) The beam emitted by the autocollimator 212 serves as the reference light. After being reflected by the third mirror 208 installed on the guide rail slider 202, it returns to the autocollimator 212, and can be used as the reference light to measure the pitch / yaw angle error in real time when the guide rail slider moves to each measurement position.

[0068] When the guide rail slider 202 scans different positions of the surface to be measured along a straight line, due to the slight height fluctuations on the surface of the mirror 211 to be measured, the measurement light will generate a slight angular change, resulting in a slight displacement of the measurement spot on the target surface of the first detector 210. Measuring this displacement can obtain the surface shape information of the mirror 211 to be measured. Also, the angular error and deflection error during the scanning movement of the guide rail slider 202 will also cause the measurement spot to be displaced on the target surface of the first detector 210, and this displacement must be subtracted to obtain the accurate surface shape of the mirror 211 to be measured. Since the autocollimator 212 is stationary relative to the ground, the detection light emitted by it will be slightly deflected due to the movement angular error of the guide rail slider 202 when it is reflected by the third mirror 208, and the autocollimator 212 measures this deflection to obtain the amount of this movement error.

[0069] Therefore, based on the two-dimensional optical scanning surface shape detection device described above, the realized two-dimensional optical scanning surface shape detection method includes:

[0070] Step S1': Provide the two-dimensional optical scanning surface shape detection device described above, and install the mirror 211 to be measured in place to start the measurement;

[0071] Step S2': When the measurement light moves with the guide rail slider 202 and irradiates each position of the mirror 211 to be measured, use the first detector 210 of the measurement light detection system to record the offset of the measurement spot at this position; use the autocollimator 212 of the reference light measurement system to simultaneously record the deflection angle of the reference light at this position;

[0072] Step S3': Determine the height distribution of the surface to be measured according to the offset of the measurement spot and the deflection angle of the reference light.

[0073] The specific content of step S3' includes:

[0074] Step S31’: Subtract the offset corresponding to the deflection angle of the reference light from the offset of the measurement light spot as the true offset of each position of the mirror 211 to be measured. Convert it according to the true offset of each position of the mirror 211 to be measured multiplied by the slope coefficient, so as to obtain the slope distribution of the mirror 211 to be measured;

[0075] Step S32’: Integrate according to the slope distribution of the mirror 211 to be measured to obtain the height distribution of the measured surface.

[0076] Thus, in the present invention, subtracting the offset corresponding to the deflection angle of the reference light from the offset of the measurement light spot can obtain the true surface undulation of the surface to be measured, and further obtain the slope distribution of the surface to be measured. Then, the height distribution of the surface to be measured can be calculated by integration.

[0077] In the present invention, the reference light measurement system can offset the influence of the tilt error of the guide rail movement on the measurement result. Therefore, in the present invention, the scanning guide rail 101 can adopt a high-precision air-floating guide rail or an ordinary mechanical guide rail.

[0078] The two-dimensional array structure π-phase plate adopts a "one"-shaped, "cross"-shaped or other types of geometric structures. The number of etching units of the two-dimensional array structure π-phase plate is such that the total etching width is greater than the total width of the mirror to be measured.

[0079] In the traditional long-range surface profiler, the size of the scanned light spot is usually <1 mm, that is, the measurement width on the surface to be measured is <1 mm. For the two-dimensional scanning structure of the present invention, as long as the number of etching units of the phase plate is sufficient to make the total etching width greater than the surface to be measured, the array light spots generated by diffraction can cover the entire width of the surface to be measured in one scan measurement. In the application of the present invention, a large-range measurement of a 500 mm × 40 mm surface to be measured has been completed, quickly realizing the two-dimensional high-precision scanning measurement of large-size high-precision optical elements, and obtaining the two-dimensional slope distribution and height distribution information of the surface to be measured.

[0080] In the above first and second embodiments, for the problem that the light spots will diffract and overlap when the lateral resolution of the original symmetric structure array phase plate is ≤1 mm, the two-dimensional array structure π-phase plate adopts Figure 6A The two-dimensional array structure π-phase plate with the shown misaligned structure, which is a misaligned array composed of multiple cross-phase structures, can be characterized by the following formula:

[0081] t(x,y) = (-1) m+n+1 ,

[0082] (x,y) ∈ [(m - 1)*L, m*L] × [(n - 1)*L, n*L]

[0083] Among them, t(x, y) represents the transmission function of the two-dimensional array structure π-phase plate, x and y represent the two-dimensional coordinates on the two-dimensional array structure π-phase plate, L is the side length of the square etching unit of the phase plate in the x direction, m is the serial number of the etching unit in the x direction, and n is the serial number of the etching unit in the y direction.

[0084] Therefore, the light intensity distribution of the far-field diffraction of the two-dimensional array structure π-phase plate 105 is a spot array with a cross-shaped dark line at the center. The Fraunhofer diffraction field of the two-dimensional array structure π-phase plate after propagating through the diffraction distance z is:

[0085] Where: x and y represent the two-dimensional coordinates on the two-dimensional array structure π-phase plate, x′ and y′ are the two-dimensional coordinates in the diffraction field, k represents the wave number, z represents the diffraction distance, λ is the transmission light wavelength, L is the side length of the square etching unit of the phase plate, M is the total number of etching units in the x direction, N is the total number of etching units in the y direction, m is the serial number of the etching unit in the x direction, and n is the serial number of the etching unit in the y direction.

[0086] The intensity distribution corresponding to the two-dimensional array structure π-phase plate is shown in the following formula, and the presented far-field diffraction pattern is Figure 6B the array cross-shaped dark lines in

[0087]

[0088] Each cross-shaped dark line (i.e., the measurement spot) has a unique position coordinate on the detector, which can be obtained through a suitable image processing algorithm; supplemented by a pixel subdivision algorithm, the resolution of the detection device can be further improved. The pixel information of the spot on the detector is obtained through the image processing algorithm, and the device needs to be further calibrated to obtain the slope value corresponding to a single pixel, that is, the calibration coefficient. The number of pixels multiplied by the calibration coefficient gives the slope information of the surface of the optical element to be measured, and further integration of the slope gives the height distribution information of the surface. The processing algorithm for each cross-shaped dark line is the same, and finally, the two-dimensional slope distribution and height distribution information of a surface of an optical element to be measured are obtained. The two-dimensional scale is determined by the scale of the two-dimensional array structure π-phase plate.

[0089] Figure 6A and Figure 6B The two groups of diffraction cross-shaped dark lines formed by the misaligned array phase plate with an etching unit width of 2 mm in

[0090] Figure 7A and Figure 7BThis is the experimental result diagram of the present invention. In this embodiment, a two-dimensional optical scanning surface shape detection device of the first embodiment is built using an array phase plate with an etching width of 44 mm. According to Figure 7A the scanning mode shown, a plane mirror of 500 mm × 40 mm is scanned and measured. After data processing, an image of the height distribution of the mirror to be measured as shown in Figure 7B is finally obtained, where PV (peak-to-valley value) = 168 nm and RMS (root mean square) = 46.4 nm.

[0091] In summary, the two-dimensional optical scanning surface shape detection device of the present invention uses a two-dimensional array structure π-phase plate to generate a far-field cross dark line array, obtains two-dimensional information on the surface of the optical element to be measured, and realizes high-precision two-dimensional scanning measurement; and adopts a reference light measurement system, which can effectively counter the influence of environmental vibrations, etc., can simultaneously obtain high-precision measurement results in the meridional and sagittal directions, is insensitive to environmental vibrations, the measurement accuracy of the system is not greatly affected by environmental vibrations, can suppress the influence of environmental air flow and temperature drift, and does not require high-precision reference optical elements or high-precision reference wavefronts.

[0092] In addition, the two-dimensional optical scanning surface shape detection device of the present invention is not only applicable to the surface quality detection of large-scale mirrors used in synchrotron radiation, but also can be applied to the surface quality detection of other types of mirrors or lenses. Since the emission power of existing semiconductor lasers is relatively high, the number of optical elements used in the system of the present invention is small, and the surfaces of the optical elements are all treated with antireflection coatings. Therefore, the reflected light intensity of the transparent surface will not affect the scanning measurement effect of the device of the present invention.

[0093] Furthermore, the two sets of diffraction cross dark lines formed by the misaligned array phase plate adopted in the present invention are staggered, and the calculated spot coordinate resolution is 1 / 2 of that of a symmetric phase plate with the same etching width. Therefore, the lateral measurement resolution can be improved.

[0094] The above-mentioned are only the preferred embodiments of the present invention and are not used to limit the scope of the present invention. Various changes can be made to the above embodiments of the present invention. All simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of the claims of the present invention patent. The content not described in detail in the present invention is all conventional technical content.

Claims

1. A two-dimensional optical scanning surface shape detection device for measuring the three-dimensional surface shape of a mirror to be measured, characterized in that, Comprising: A measurement light detection system, which includes a laser, a collimating lens, a two-dimensional array structure π-phase plate, and a first beam splitter prism arranged in sequence along the optical path on the first optical axis, and a first reflector, a second lens, and a first detector arranged in sequence on the second optical axis; A reference light measurement system, which includes a slidable positioning part and a fixed positioning part spaced apart, configured to obtain the angular offset information between the slidable positioning part and the fixed positioning part; and A scanning system, which includes a guide rail slide, on which the measurement light detection system and the slidable positioning part are mounted.

2. The two-dimensional optical scanning surface shape detection device according to claim 1, wherein The slidable positioning part of the reference light measurement system includes a second beam splitter prism, a third lens, and a second detector arranged in sequence on the third optical axis, and the fixed positioning part of the reference light measurement system includes a second reflector fixed relative to the ground; Alternatively, the slidable positioning part of the reference light measurement system includes the first reflector, the second lens, and the first detector, and the fixed positioning part of the reference light measurement system includes a second reflector fixed relative to the ground.

3. The two-dimensional optical scanning surface shape detection device according to claim 2, wherein The first reflector is configured to reflect the light from the first beam splitter prism to the second lens; the first beam splitter prism is configured to split the light from the two-dimensional array structure π-phase plate to be respectively propagated to the second reflector and the mirror under test, and is configured to reflect the light from the mirror under test to the first reflector.

4. The two-dimensional optical scanning surface shape detection device according to claim 1, characterized in that, The slidable positioning part of the reference light measurement system includes a third reflector, and the fixed positioning part of the reference light measurement system includes a self-collimator fixed relative to the ground.

5. The two-dimensional optical scanning surface shape detection device according to claim 1, characterized in that The mirror under test is arranged downstream of the first beam splitter prism on the first optical axis and is fixed relative to the ground; the fixed positioning part is fixed relative to the ground; and the shape of the mirror under test includes a plane, a spherical surface, and a cylindrical surface.

6. The two-dimensional optical scanning surface shape detection device according to claim 1, wherein The scanning system further includes a scanning guide rail, which adopts a high-precision air-floating guide rail or a mechanical guide rail, and the guide rail slide is mounted on the scanning guide rail.

7. The two-dimensional optical scanning surface shape detection device according to claim 1, wherein The two-dimensional array structure π-phase plate is in a linear shape or a cross shape, and the number of etching units of the two-dimensional array structure π-phase plate makes the total etching width greater than the total width of the mirror under test.

8. The two-dimensional optical scanning surface shape detection device according to claim 1, wherein The two-dimensional array structure π-phase plate adopts a two-dimensional array structure π-phase plate with a dislocation structure, and the two sets of diffracted cross dark lines formed by it are staggered to improve the lateral measurement resolution.

9. A two-dimensional optical scanning surface shape detection method, characterized in that Comprising: Step S1: Provide the two-dimensional optical scanning surface shape detection device according to any one of claims 1-8, and install the mirror under test in place to start the measurement; Step S2: When the measurement light moves with the guide rail slide and irradiates each position of the mirror under test, use the measurement light detection system to record the offset of the measurement light spot at this position; use the reference light measurement system to simultaneously record the offset of the reference light spot or the deflection angle of the reference light at this position; Step S3: Determine the height distribution of the surface under test according to the offset of the measurement light spot and the offset of the reference light spot.

10. The two-dimensional optical scanning surface shape detection method according to claim 9, characterized in that, The specific content of step S3 includes: Step S31: Subtract the offset of the reference light spot or the offset corresponding to the deflection angle of the reference light from the offset of the measured light spot as the true offset of each position of the mirror under test. According to the true offset of each position of the mirror under test, multiply by the slope coefficient for conversion to obtain the slope distribution of the mirror under test. Step S32: Integrate according to the slope distribution of the mirror under test to obtain the height distribution of the measured surface.

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