Mirror surface shape measurement system and method based on ultrafast high-precision laser scanning

Abstract

The application discloses a mirror surface shape measurement system and method based on superfast high-precision laser scanning, and the system and method solve the problems of low surface shape detection precision, small surface shape detection size, insufficient absolute positioning precision and susceptibility to vibration in the environment in the prior art surface shape detection technology, and specifically comprise a pulse laser, a beam expanding and light splitting module, an interference module, a four-step phase shift module, a detection module, a receiving module and an upper computer; the pulse laser emits pulse laser; the beam expanding and light splitting module divides the pulse laser into 0-order diffraction light and ±1-order diffraction light which are parallel to each other; the interference module receives the 0-order diffraction light and the ±1-order diffraction light to form multi-order diffraction interference light; the four-step phase shift module performs four-step phase shift light splitting on the multi-order diffraction interference light; the detection module receives the phase shift light beams, and performs photoelectric conversion to form 0-order phase shift signals, +1-order phase shift signals and -1-order phase shift signals; the receiving module receives the 0-order phase shift signals, the +1-order phase shift signals and the -1-order phase shift signals; and the upper computer is used for restoring the surface shape information of a mirror to be measured.

Description

Technical Field

[0001] The present invention relates to a mirror surface shape measurement system and method, and in particular to a mirror surface shape measurement system and method based on ultrafast high-precision laser scanning. Background Art

[0002] Surface measurement using pulsed lasers is mainly based on a large-aperture measuring beam composed of a Michelson structure, while the laser scanning interferometer uses a laser beam to scan the measurement substrate, continuously records the surface information of the measured surface, and uses the shape and position of the laser beam interference fringes to feedback the height information of the measured surface to restore the measured surface information. Compared with the large-aperture surface measurement of Zygo interferometers and 4D interferometers, it avoids the need to process ultra-precision standard mirrors, and can further improve the surface aperture of the scanning mirror as the scanning range and accuracy increase. In response to the technical problem that the surface size continues to increase but the measurement accuracy continues to decrease in actual measurement, surface scanning using ultrashort pulse lasers and dual-cavity mirror laser probes is one of the key technologies to solve this problem.

[0003] In surface scanning interferometer research, Michelson, Miller, Linnik, and Fizeau types are the most common. A prominent market device is the UK-based Taylor Luphoscan 850HD interferometer, which boasts a measuring aperture of up to 850mm, a height range of up to 210mm, surface shape error accuracy of up to λ / 20, an RMS better than 5nm, and a maximum surface slope variation of ±8°. With real-time compensation using an active anti-vibration system, temperature sensors, and air pressure sensors, it can achieve high repeatability of 40nm. Other options include the 650mm x 650mm sub-nanometer scanning interferometer from Zygo Corporation in the United States and the high-precision laser interferometer from Zeiss in Germany, with an RMS better than 0.02nm. In scientific research, the INF800-LP-WM laser interferometer from Beijing Institute of Technology and Taike Corporation stands out. It features an effective aperture of 800mm, a PV better than λ / 12, and an RMS repeatability better than 0.63nm. It also utilizes TMC air flotation for real-time vibration compensation. In addition, there are also the National University of Defense Technology's spliced ​​interferometer, the Chengdu Institute of Optoelectronics' processing capabilities below 300mm, and the Institute of Optoelectronics' 600mm aperture 24-inch laser interferometer. Currently, EUV lithography machines have reached 3nm manufacturing precision, even at the PM level. Therefore, multi-cross technology is needed to address a series of challenges, including low surface monitoring accuracy, high surface processing difficulty, difficult surface calibration, and the influence of environmental vibration, temperature, and air pressure interference. Summary of the Invention

[0004] The purpose of the present invention is to provide a mirror surface measurement system and method based on ultrafast high-precision laser scanning to solve the technical problems existing in existing surface detection technology, such as low surface detection accuracy, small surface detection size, insufficient absolute positioning accuracy, and susceptibility to interference from vibration, air pressure and temperature in the environment.

[0005] In the present invention, first, a 500ps ultrashort pulse laser is used for interferometric measurement; second, multiple reflections of a dual-cavity mirror are used to improve measurement accuracy; third, phase coupling of the ±1st-order diffraction light of a one-dimensional transmission grating is used to reduce the influence of environmental errors; fourth, the 0th-order diffraction light of a one-dimensional transmission grating is used for absolute positioning and real-time precise positioning measurement, so as to achieve the purpose of ultra-precision surface measurement.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A mirror surface measurement system based on ultrafast high-precision laser scanning is used to measure the surface shape of the mirror to be measured. Its special features include: a pulsed laser, a beam expansion and splitting module, an interference module, a four-step phase shift module, a detection module, a receiving module and a host computer;

[0008] The pulse laser emits pulse laser;

[0009] The beam expansion and splitting module splits the pulsed laser into parallel 0th order diffraction light and ±1st order diffraction light;

[0010] The interference module receives the 0th order diffraction light and the ±1st order diffraction light, and makes the three enter the measurement optical path and the reference optical path of the interference module respectively for interference, thereby forming multi-order diffraction interference light; the mirror to be measured is arranged on the measurement optical path of the 0th order diffraction light and the ±1st order diffraction light;

[0011] The four-step phase shift module is used to perform four-step phase shift splitting on the multi-order diffraction interference light to form a phase-shifted beam; the phase-shifted beam includes 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 0°, 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 90°, 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 180°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 270°;

[0012] The detection module is used to receive the phase-shifted light beam and perform photoelectric conversion to form a 0-level phase-shifted signal, a +1-level phase-shifted signal, and a -1-level phase-shifted signal;

[0013] The receiving module receives the 0-level phase shift signal, the +1-level phase shift signal and the -1-level phase shift signal respectively, and uploads them to the host computer;

[0014] The host computer is used to perform phase unwrapping calculation on the 0-level phase shift signal, the +1-level phase shift signal and the -1-level phase shift signal, display linear measurement data, and then use the linear measurement data to restore the surface information of the mirror to be measured.

[0015] Furthermore, the pulse laser is an ultrashort pulse laser, which is used to emit 532nm pulse laser with a repetition frequency of 1-1000Hz, a pulse width of 500ps, and a single pulse energy of 1mJ.

[0016] Furthermore, the beam expansion and splitting module includes a first converging lens, a beam expansion device, a one-dimensional transmission grating, a second converging lens and an aperture, all of which are located in the optical path of the pulsed laser and are arranged in sequence along the emission direction thereof;

[0017] The first converging lens is used to make the pulsed laser incident on the beam expanding device in parallel;

[0018] The beam expansion device is used to expand the parallel incident pulse laser beam;

[0019] The one-dimensional transmission grating is used to form 0th order diffraction light and ±1st order diffraction light;

[0020] The second converging lens is used to make the 0th order diffracted light and the ±1st order diffracted light respectively incident on the aperture in parallel;

[0021] The aperture is used to isolate the overlapping part of the 0th order diffraction light and the ±1st order diffraction light beams, while changing the energy thereof and the aperture size of the incident light spot.

[0022] Furthermore, the interference module includes a first polarization beam splitter prism having four sides, wherein the first side is opposite to the third side, and the second side is opposite to the fourth side;

[0023] The first side corresponds to the aperture and is used to receive the 0th order diffraction light and the ±1st order diffraction light;

[0024] The second side corresponds to the four-step phase shift module, and a half-wave plate is provided on the optical path between the second side and the four-step phase shift module for emitting multi-order diffraction interference light;

[0025] The third side is provided with a second quarter wave plate, a second partially transmitting cavity mirror and a high reflective mirror in sequence along a direction away from the third side, forming a reference optical path;

[0026] The fourth side is provided with a first quarter wave plate, a first partially transmissive cavity mirror, and a first focusing lens in sequence along a direction away from the fourth side; a side of the first focusing lens away from the first partially transmissive cavity mirror is used to set the mirror to be measured; the first quarter wave plate, the first partially transmissive cavity mirror, the first focusing lens, and the mirror to be measured constitute a measurement optical path;

[0027] The first partially transmissive cavity mirror and the second partially transmissive cavity mirror are both double cavity mirrors, and the sides of the two mirrors close to the first polarization beam splitter prism are coated with a reflective film and the other sides are coated with an antireflection film, the reflectivity of the reflective film is ≥90%, and the transmittance of the antireflection film is ≥90%;

[0028] The splitting surface of the first polarization beam splitter prism is equidistant from the rear surfaces of the first partially transmissive cavity mirror and the second partially transmissive cavity mirror; the distance from the rear surface of the first partially transmissive cavity mirror to the reflective surface of the mirror to be measured is equal to the distance from the rear surface of the second partially transmissive cavity mirror to the reflective surface of the high-reflection mirror; the rear surface is the surface away from the first polarization beam splitter prism.

[0029] Furthermore, the four-step phase shift module includes a beam splitter prism, a second polarization beam splitter prism, and a third polarization beam splitter prism;

[0030] The beam splitter prism is used to split the energy of the multi-order diffraction interference light emitted by the half-wave plate to form reflected light and transmitted light; the beam splitter prism has a splitting ratio of 5:5;

[0031] The second polarization beam splitter prism is located on the optical path of the transmitted light, and a third quarter-wave plate is provided on the optical path between the second polarization beam splitter prism and the beam splitter prism, for performing polarization beam splitting on the transmitted light to form 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 90°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 270°;

[0032] The third polarization beam splitter prism is located on the optical path of the reflected light, and a fourth quarter-wave plate is provided on the optical path between the third polarization beam splitter prism and the beam splitter prism, for performing polarization beam splitting on the reflected light to form 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 0°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 180°.

[0033] Furthermore, the polarization angles of the first quarter wave plate, the second quarter wave plate, the third quarter wave plate, and the fourth quarter wave plate are all 45°.

[0034] Furthermore, the detection module includes first to twelfth photodetectors;

[0035] The first photodetector is used to receive the 0th order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first 0th order phase shift signal;

[0036] The second photodetector is used to receive the 0th order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second 0th order phase shift signal;

[0037] The third photodetector is used to receive the 0th order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a third 0th order phase shift signal;

[0038] The fourth photodetector is used to receive the 0th order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth 0th order phase shift signal;

[0039] The fifth photodetector is used to receive the +1-order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first +1-order phase shift signal;

[0040] The sixth photodetector is used to receive the +1st order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second +1st order phase shift signal;

[0041] The seventh photodetector is used to receive the +1 order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a third +1 order phase shift signal;

[0042] The eighth photodetector is used to receive the +1-order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth +1-order phase shift signal;

[0043] The ninth photodetector is used to receive the -1 order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first -1 order phase shift signal;

[0044] The tenth photodetector is used to receive the -1st order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second -1st order phase shift signal;

[0045] The eleventh photodetector is used to receive the -1 order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a third -1 order phase shift signal;

[0046] The twelfth photodetector is used to receive the -1 order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth -1 order phase shift signal;

[0047] The first to fourth 0-level phase-shifted signals are the 0-level phase-shifted signals; the first to fourth +1-level phase-shifted signals are the +1-level phase-shifted signals; and the first to fourth -1-level phase-shifted signals are -1-level phase-shifted signals.

[0048] Further, the receiving module includes a first oscilloscope, a second oscilloscope and a third oscilloscope;

[0049] The first oscilloscope is used to receive the 0-level phase shift signal and upload it to the host computer;

[0050] The second oscilloscope is used to receive the +1-level phase shift signal and upload it to the host computer;

[0051] The third oscilloscope is used to receive the -1 level phase shift signal and upload it to the host computer.

[0052] Furthermore, the interference module further includes a second focusing lens;

[0053] The second focusing lens is arranged on the optical path between the second partially transmitting cavity mirror and the high reflective mirror.

[0054] A mirror surface shape measurement method based on ultrafast high-precision laser scanning, using the above-mentioned mirror surface shape measurement system based on ultrafast high-precision laser scanning, is characterized in that it includes the following steps:

[0055] Step 1: Without installing the mirror to be tested and the high reflective mirror, the pulse laser emits pulse laser;

[0056] Step 2: Adjust the pulse laser so that its emitted pulse laser is horizontally incident on the beam expansion and spectrometer module. The beam expansion and spectrometer module divides the pulse laser into mutually parallel 0th order diffraction light and ±1st order diffraction light. Adjust the interference module so that the 0th order diffraction light and the 0th order reflected light of the ±1st order diffraction light can completely enter the center of the detection photosensitive surface of the detection module after passing through the interference module and the four-step phase shift module, completing the preliminary surface positioning;

[0057] Step 3: Install a high-reflection mirror and adjust its spatial position so that the multi-order light of the 0th-order diffraction light and the multi-order light of the ±1st-order diffraction light formed on the reference light path of the interference module can be completely incident on the center of the detection photosensitive surface of the detection module, completing the precise surface positioning of the reference light path;

[0058] Step 4: Install the mirror to be measured and adjust its spatial position so that the multi-order light of the 0th order diffraction light and the multi-order light of the ±1st order diffraction light formed on the measurement optical path of the interference module are parallel to and coincide with the light formed on the reference optical path, and can be completely incident on the center of the detection photosensitive surface of the detection module, thereby completing the precise surface positioning of the measurement optical path;

[0059] Step 5: Repeatedly cross linearly move the mirror to be tested along the horizontal and vertical lines. After each movement, the detection module obtains the 0-level phase shift signal, +1-level phase shift signal, and -1-level phase shift signal of the mirror to be tested, and uploads them to the host computer through the receiving module. The 0-level phase shift signal is used as the control group, and the ±1-level phase shift signal is calibrated in real time for surface interferometry information.

[0060] Step 6: The host computer performs phase unwrapping calculations on all acquired 0-level phase shift signals, +1-level phase shift signals, and -1-level phase shift signals, displays multiple sets of linear measurement data, and then uses the multiple sets of linear measurement data to restore the surface information of the mirror to be measured.

[0061] Beneficial effects of the present invention:

[0062] 1. The mirror surface measurement system and method based on ultrafast high-precision laser scanning provided by the present invention improve the surface detection accuracy, can adapt to larger surface detection sizes, and avoid the influence of phase noise and environmental errors.

[0063] 2. The present invention utilizes an ultrashort pulse laser with a pulse width of 500 ps, ​​which enables the resolution in the time domain to reach the ps level; secondly, the present invention uses a dual-cavity mirror structure and consistent optical path characteristics to achieve multiple reflection measurement. Each reflection can carry surface shape information once, greatly improving the surface shape measurement accuracy; then, the present invention uses a one-dimensional transmission grating, and through phase decoupling of the ±1st order diffraction light, reduces the influence of air pressure, vibration and temperature during the propagation of the light beam, further improving the surface shape measurement accuracy.

[0064] 3. The present invention utilizes multiple reflections of a dual-cavity mirror and intends to use pulse information from 100 reflections to perform 100 surface shape information superpositions. At the same time, by utilizing the cross-linear movement of the measuring mirror, the measurement size can be expanded as the measuring mirror moves. Through multiple continuous scanning measurements, the surface shape information of the entire measuring mirror can be restored, thereby improving the detection size of the measured surface shape.

[0065] 4. In the present invention, firstly, the 0th order light of the 0th order diffraction light and the 0th order light of the ±1st order diffraction light of the partially transmitted cavity mirror of the dual cavity mirror in the laser probe are used to perform preliminary precision surface positioning; secondly, the 0th order diffraction light in the laser probe is used to perform precise surface positioning; thirdly, the 0th order diffraction light is used to perform real-time surface interference information calibration under the state of real-time measurement of multi-order light of the ±1st order diffraction light, so as to achieve the purpose of ultra-precision interferometer surface detection and positioning measurement.

[0066] 5. First, by using ultrashort pulse lasers, each pulse has a width of 500ps, while the width of 100 round-trip pulses is approximately 300ps. Each pulse recognition can form an equal comb-shaped sequence measurement signal, and equal sequence recognition can avoid the influence of phase noise. Second, by utilizing the mutual multiple reflections and interference of ±1-order diffraction light, after phase decoupling, equal phase recognition information of 2Δφ, 4Δφ...2nΔφ is formed within a pulse. Third, a four-step phase shift is adopted, and different diffraction interference information is formed through different channels. The difference in the effective recognition time of the pulse signal and the effective recognition time of stray light is achieved, effectively avoiding the influence of stray light on the detection results. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 1 is a schematic structural diagram of a first embodiment of a mirror surface shape measurement system and method based on ultrafast high-precision laser scanning according to the present invention;

[0068] Figure 2 Schematic diagram of light beam diffraction of a one-dimensional transmission grating in Example 1 of the present invention;

[0069] Figure 3 1 is a schematic diagram of the transmission of the light beam of the second portion of the reference light path through the multi-stage reflected light of the cavity mirror in the first embodiment of the present invention;

[0070] Figure 4 Schematic diagram of the transmission of the light beam of the multi-stage reflected light of the cavity mirror in the first part of the measurement light path in the first embodiment of the present invention;

[0071] Figure 5 It is a structural schematic diagram of embodiment 2 of the mirror surface shape measurement system and method based on ultrafast high-precision laser scanning of the present invention.

[0072] Figure Number:

[0073] 1-Pulse laser, 201-First converging lens, 202-Beam expander, 203-One-dimensional transmission grating, 204-Second converging lens, 205-Aperture, 3-Interference module, 4-Four-step phase shift module, 5-Detection module, 6-Receiving module, 301-First polarization beam splitter prism, 404-Second polarization beam splitter prism, 405-Third polarization beam splitter prism, 305-First quarter wave plate, 302-Second quarter wave plate, 402-Third quarter wave plate, 403-Fourth quarter wave plate, 306-First partial transmission cavity mirror, 303-Second partial transmission cavity mirror, 307-First focusing lens, 309-Second Focusing lens, 304-high reflective mirror, 8-mirror to be measured, 308-half wave plate, 401-beam splitter prism, 501-first photodetector, 502-second photodetector, 503-third photodetector, 504-fourth photodetector, 505-fifth photodetector, 506-sixth photodetector, 507-seventh photodetector, 508-eighth photodetector, 509-ninth photodetector, 510-tenth photodetector, 511-eleventh photodetector, 512-twelfth photodetector, 601-first oscilloscope, 602-second oscilloscope, 603-third oscilloscope, 7-host computer. DETAILED DESCRIPTION

[0074] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0075] Example 1:

[0076] The embodiment of the present invention provides a mirror surface shape measurement system based on ultrafast high-precision laser scanning, which is used for measuring the surface shape of the mirror 8 to be measured. Figure 1 As shown, it includes a pulse laser 1, a beam expansion and splitting module 2, an interference module 3, a four-step phase shift module 4, a detection module 5, a receiving module 6 and a host computer 7;

[0077] The pulse laser 1 is an ultrashort pulse laser, which is used to emit 532nm pulse laser with a repetition frequency of 1-1000Hz, a pulse width of 500ps, and a single pulse energy of 1mJ.

[0078] The beam expansion and spectrometer module 2 includes a first converging lens 201, a beam expansion device 202, a one-dimensional transmission grating 203, a second converging lens 204 and an aperture 205, all of which are located in the optical path of the pulsed laser and are arranged in sequence along its output direction; the first converging lens 201 is used to make the pulsed laser incident on the beam expansion device 202 in parallel; the beam expansion device 202 is used to expand the parallel-incident pulsed laser; the one-dimensional transmission grating 203 is used to form 0th-order diffraction light and ±1st-order diffraction light; the second converging lens 204 is used to make the 0th-order diffraction light and ±1st-order diffraction light respectively incident on the aperture 205 in parallel; the aperture 205 is used to isolate the overlapping part of the beams of the 0th-order diffraction light and the ±1st-order diffraction light, and at the same time change its energy size and the aperture size of the incident light spot.

[0079] The interference module 3 receives the 0th order diffraction light and the ±1st order diffraction light, and makes the three enter the measurement optical path and the reference optical path of the interference module 3 respectively for interference, thereby forming multi-order diffraction interference light; the mirror to be measured 8 is arranged on the measurement optical path of the 0th order diffraction light and the ±1st order diffraction light; the interference module 3 includes a first polarization splitting prism 301 with four sides, the first side of which is opposite to the third side, and the second side is opposite to the fourth side; the first side corresponds to the aperture 205; the second side corresponds to the four-step phase shift module 4, and a half-wave plate 308 is arranged on the optical path between the second side and the four-step phase shift module 4; the third side is provided with a second quarter-wave plate 302, a second partially transmitting cavity mirror 303 and a high reflective mirror 304 in sequence along the direction away from the third side; the fourth side is provided with a first quarter-wave plate 305, a first partially transmitting cavity mirror 303 and a high reflective mirror 304 in sequence along the direction away from the fourth side A partially transmitting cavity mirror 306 and a first focusing lens 307; the side of the first focusing lens 307 away from the first partially transmitting cavity mirror 306 is used to set the mirror to be measured 8; the first partially transmitting cavity mirror 306 and the second partially transmitting cavity mirror 303 are both double-cavity mirrors, and the side of both close to the first polarization beam splitter prism 301 is coated with a reflective film, and the other side is coated with an anti-reflection film, the reflectivity of the reflective film is ≥90%, and the transmittance of the anti-reflection film is ≥90%; the splitting surface of the first polarization beam splitter prism 301 is equidistant from the rear surfaces of the first partially transmitting cavity mirror 306 and the second partially transmitting cavity mirror 303; the distance from the rear surface of the first partially transmitting cavity mirror 306 to the reflective surface of the mirror to be measured 8 is equal to the distance from the rear surface of the second partially transmitting cavity mirror 303 to the reflective surface of the high reflector 304; the rear surface is the surface away from the first polarization beam splitter prism 301.

[0080] The first polarization splitting prism 301 performs orthogonal polarization splitting, transmitting P light and reflecting S light;

[0081] The first quarter wave plate 305 and the second quarter wave plate 302 are used to change the polarization state, and the P light and the S light become circularly polarized light, and the polarization angle is set to 45°;

[0082] The first focusing lens 307 is used to converge the light beam;

[0083] High reflective mirror 304 is coated with high reflective film, with a reflectivity of ≥98%;

[0084] The half wave plate 308 is used to change the energy of the P light and the S light;

[0085] The four-step phase shift module 4 is used to perform four-step phase shifting and splitting on the multi-order diffraction interference light to form a phase-shifted beam; the phase-shifted beam includes the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 0°, the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 90°, the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 180°, and the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 270°; the four-step phase shift module 4 includes a beam splitter prism 401, a second polarization beam splitter prism 404, and a third polarization beam splitter prism 405; the beam splitter prism 401 is used to perform energy splitting on the multi-order diffraction interference light emitted by the half wave plate 308 to form reflected light and transmitted light; the splitting ratio of the beam splitter prism 401 is 5:5; the second polarization beam splitter prism The mirror 404 is located on the optical path of the transmitted light, and a third quarter-wave plate 402 is provided on the optical path between the second polarization beam splitter prism 404 and the beam splitter prism 401, for performing polarization beam splitting on the transmitted light to form 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 90°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 270°; the third polarization beam splitter prism 405 is located on the optical path of the reflected light, and a fourth quarter-wave plate 403 is provided on the optical path between the third polarization beam splitter prism 405 and the beam splitter prism 401, for performing polarization beam splitting on the reflected light to form 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 0°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 180°.

[0086] The second polarization splitting prism 404 and the third polarization splitting prism 405 perform orthogonal polarization splitting, transmitting the P light and reflecting the S light;

[0087] The third quarter wave plate 402 and the fourth quarter wave plate 403 are used to change the polarization state, so that the P light and the S light become circularly polarized light, and the polarization angles are both set to 45°;

[0088] The detection module 5 is used to receive the phase-shifted light beam and perform photoelectric conversion to form a 0-order phase-shift signal, a +1-order phase-shift signal and a -1-order phase-shift signal; the detection module 5 includes first to twelfth photodetectors; the first photodetector 501 is used to receive the 0-order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first 0-order phase-shift signal; the second photodetector 502 is used to receive the 0-order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second 0-order phase-shift signal; the third photodetector 503 is used to receive the 0-order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a second 0-order phase-shift signal. The 0th order diffraction interference light with a phase of 270° is received and photoelectrically converted to form a third 0th order phase shift signal; the fourth photodetector 504 is used to receive the 0th order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth 0th order phase shift signal; the fifth photodetector 505 is used to receive the +1st order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first +1st order phase shift signal; the sixth photodetector 506 is used to receive the +1st order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second +1st order phase shift signal; the seventh photodetector 506 is used to receive the +1st order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second +1st order phase shift signal; The electrical detector 507 is used to receive the +1 order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a third +1 order phase shift signal; the eighth photodetector 508 is used to receive the +1 order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth +1 order phase shift signal; the ninth photodetector 509 is used to receive the -1 order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first -1 order phase shift signal; the tenth photodetector 510 is used to receive the -1 order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a first -1 order phase shift signal. Photoelectric conversion is performed to form a second -1 order phase-shifted signal; the eleventh photodetector 511 is used to receive the -1 order diffraction interference light with a phase of 90°, and perform photoelectric conversion to form a third -1 order phase-shifted signal; the twelfth photodetector 512 is used to receive the -1 order diffraction interference light with a phase of 270°, and perform photoelectric conversion to form a fourth -1 order phase-shifted signal; the first to fourth 0th order phase-shifted signals are 0th order phase-shifted signals; the first to fourth +1th order phase-shifted signals are +1th order phase-shifted signals; and the first to fourth -1st order phase-shifted signals are -1th order phase-shifted signals.

[0089] The receiving module 6 receives the 0-order phase shift signal, the +1-order phase shift signal and the -1-order phase shift signal respectively, and uploads them to the host computer 7; the receiving module 6 includes a first oscilloscope 601, a second oscilloscope 602 and a third oscilloscope 603; the first oscilloscope 601 is used to receive the 0-order phase shift signal, that is, the interference measurement signal of the 0-order diffracted light, and upload it to the host computer 7, and the four-step phase shift information comes from: the first photodetector 501 to the fourth photodetector 504 respectively; the second oscilloscope 602 is used to receive the +1-order phase shift signal, that is, the interference measurement signal of the +1-order diffracted light, and the four-step phase shift information comes from: the fifth photodetector 505 to the eighth photodetector 508 respectively, and uploads it to the host computer 7; the third oscilloscope 603 is used to receive the -1-order phase shift signal, that is, the interference measurement signal of the -1-order diffracted light, and the four-step phase shift information comes from: the ninth photodetector 509 to the twelfth photodetector 512 respectively, and uploads it to the host computer 7.

[0090] The host computer 7 is used to perform phase unwrapping calculation on the interference measurement signal (i.e., the 0-level phase shift signal, the +1-level phase shift signal, and the -1-level phase shift signal), display the linear measurement data, and then use multiple linear measurement data to restore the surface information of the mirror to be measured 8.

[0091] Combine Figure 1-Figure 4 As shown, the pulsed laser light emitted by the pulsed laser 1 is transformed into a horizontal beam by the first converging lens 201, the incident spot size is expanded by the beam expander 202, and then incident on the one-dimensional transmission grating 203 for splitting into 0th order diffraction light and ±1st order diffraction light. The three beams are transformed into parallel beams by the second converging lens 204, filtered by the aperture 205, and split by the first polarization beam splitting prism 301, entering the reference optical path and the measurement optical path respectively.

[0092] The reference optical path includes a second quarter wave plate 302, a second partially transmitting cavity mirror 303 and a high reflective mirror 304;

[0093] The transmitted light P light entering the reference optical path is transmitted through the second quarter wave plate 302, and the polarization state is changed. The P light becomes circularly polarized light, and is split in the second part of the transmission cavity mirror 303 to form reflected light and transmitted light; the reflected light is transmitted through the second quarter wave plate 302, and the polarization state is changed. The circularly polarized light becomes S light, which is reflected by the first polarization splitting prism 301 and transmitted by the half wave plate 308 to form 0-level light incident on the four-step phase shift module 4; the transmitted light is reflected by the high reflector 304, returns to the original path, and is split in the second part The transmission cavity mirror 303 splits the light, forming transmitted light and reflected light again. The transmitted light passes through the second quarter-wave plate 302, where its polarization state is changed, and the circularly polarized light becomes S light. This light is then reflected by the first polarization beam splitter prism 301 and transmitted through the half-wave plate 308, forming level 1 light that is incident on the four-step phase shift module 4. The reflected light is reflected multiple times by the second partial transmission cavity mirror 303 and the high-reflection mirror 304, each time generating a re-emitted signal, and thus sequentially generating level 2 light, level 3 light, level 4 light, and so on, where n is greater than or equal to 6.

[0094] The measuring optical path includes a first quarter wave plate 305, a first partially transmitting cavity mirror 306, a first focusing lens 307 and a mirror to be measured 8;

[0095] The reflected light S entering the measurement optical path is transmitted through the first quarter-wave plate 305, changing its polarization state. The S light becomes circularly polarized light and is split by the first partial transmission cavity mirror 306. The reflected light forms the 0th order light and the transmitted light forms the 1st order light.

[0096] The 0-order light is transmitted through the first quarter-wave plate 305, and its polarization state is changed. The circularly polarized light is converted into P light, which is then transmitted through the first polarization beam splitter prism 301 and the half-wave plate 308, and is incident on the four-step phase shift module 4.

[0097] The first-order light is converged by the first focusing lens 601, reflected by the test mirror 8, and emitted at a reflection angle opposite to the incident angle. It is parallel to the first focusing lens 307 and split by the first partially transmitting cavity mirror 306 to form transmitted light and reflected light. The transmitted light is transmitted by the first quarter-wave plate 401, where its polarization state is changed. The circularly polarized light is converted to P light. It is then transmitted by the first polarization splitting prism 301 and the half-wave plate 308 to form the first-order light that is incident on the four-step phase shift module 4. The reflected light is reflected multiple times by the first partially transmitting cavity mirror 306, the first focusing lens 307, and the test mirror 8, and a retroreflection signal is obtained each time, thereby obtaining the second-order light, the third-order light, the fourth-order light, and so on, the n-order light.

[0098] The multi-level light of the reference light path and the measurement light path is combined and then split by the beam splitter prism 401. The polarization state of the first transmitted light is changed by the third quarter-wave plate 402, and the polarization is split by the second polarization splitter prism 404. The second transmitted light is incident on the fourth photodetector 504, the eighth photodetector 508, and the twelfth photodetector 512. The second reflected light is incident on the third photodetector 503, the seventh photodetector 507, and the eleventh photodetector 511. The polarization state of the first reflected light is changed by the fourth quarter-wave plate 403, and the polarization is split by the third polarization splitter prism 405. The third transmitted light is incident on the first photodetector 501, the fifth photodetector 505, and the ninth photodetector 509. The third reflected light is incident on the second photodetector 502, the sixth photodetector 506, and the tenth photodetector 510.

[0099] The optical paths of the three beams of light passing through the splitting surface of the first polarization beam splitting prism 301 to the rear surface of the first partially transmissive cavity mirror 306 and the rear surface of the second partially transmissive cavity mirror 303 are equal;

[0100] The optical path from the rear surface of the first partially transmissive cavity mirror 301 on the measuring optical path to the front surface of the mirror to be measured 8 is equal to the optical path from the rear surface of the second partially transmissive cavity mirror 303 on the reference optical path to the front surface of the high reflective mirror 304;

[0101] The multi-level reference light on the reference light path are:

[0102] 0th order diffraction light: 0th order light, 1st order light, 2nd order light...nth order light;

[0103] +1st order diffraction light: 0th order light, 1st order light, 2nd order light...nth order light;

[0104] -1st order diffraction light: 0th order light, 1st order light, 2nd order light...nth order light;

[0105] The multi-level reference light on the measurement optical path are:

[0106] 0th order diffraction light: 0th order light, 1st order light, 2nd order light...nth order light;

[0107] Multi-order reflected light on the left: 0th order light of +1st order diffraction light, 1st order light of -1st order diffraction light, 2nd order light of +1st order diffraction light…(-1) n n-order light of the first-order diffracted light;

[0108] Multi-order reflected light on the right: 0th order light of -1st order diffraction light, 1st order light of +1st order diffraction light, 2nd order light of -1st order diffraction light…(-1) n+1 n-order light of the first-order diffracted light;

[0109] When the reflected light is reflected by the measuring mirror 8 once, it carries the mirror phase information Δφ once. After n reflections, the mirror phase information it carries is nΔφ.

[0110] When the structures of the reference optical path and the measurement optical path are inconsistent, the phase measurement information of the second photodetector 502 and the third photodetector 503 of the interference beam of the multi-level reflected light are: nΔφ and -nΔφ respectively. Phase coupling operation is performed on the two beams of interference information to reduce the influence of environmental errors in the measurement system. The phase coupling information is: 2nΔφ.

[0111] The first photodetector 501, the second photodetector 502, the third photodetector 503 and the fourth photodetector 504 respectively receive: 0°, 90°, 180° and 270° phase shifts of the 0th order diffracted light; the 0th order light, 1st order light, 2nd order light, 3rd order light, 4th order light ... nth order light of the 0th order diffracted light on the reference optical path; the 0th order light, 1st order light, 2nd order light, 3rd order light, 4th order light ... nth order light of the 0th order diffracted light on the measurement optical path; interfere with each other, convert the light into photoelectric signals, and transmit them to the first oscilloscope 601, and transmit them to the host computer 7;

[0112] The fifth photodetector 505, the sixth photodetector 506, the seventh photodetector 507, and the eighth photodetector 508 respectively receive: the ±1st order diffracted light with phase shifts of 0°, 90°, 180°, and 270°; the 0th order light, 1st order light, 2nd order light, 3rd order light, 4th order light, ... nth order light of the +1st order diffracted light on the reference optical path; the 0th order light, -1st order light, +1st order diffracted light 2nd order light, ... (-1) on the measurement optical path. n The n-order light of the diffracted light interferes with each other, is photoelectrically converted to the second oscilloscope 602, and is transmitted to the host computer 7;

[0113] The ninth photodetector 509, the tenth photodetector 510, the eleventh photodetector 511, and the twelfth photodetector 512 respectively receive: the phase shifts of ±1st order diffracted light of 0°, 90°, 180°, and 270°; the 0th order light, 1st order light, 2nd order light, 3rd order light, 4th order light, ... nth order light of -1st order diffracted light on the reference optical path; the 0th order light, 1st order light of +1st order diffracted light, 2nd order light of -1st order diffracted light, ... (-1) on the measurement optical path. n+1 The n-order light of the diffracted light interferes with each other, is photoelectrically converted to the third oscilloscope 603, and is transmitted to the host computer 7;

[0114] The reference light path is, from top to bottom, +1-order diffraction light, 0-order diffraction light, and -1-order diffraction light. The three diffraction light beams are split by the second partially transmitting cavity mirror 303, and the first reflected light returns along the original path to form 0-order light of +1-order diffraction light, 0-order diffraction light, and -1-order diffraction light; the first transmitted light is vertically incident on the high-reflection mirror 304, returns along the original path, and is split by the second partially transmitting cavity mirror 303. The second transmitted light forms 1-order light of +1-order diffraction light, 0-order diffraction light, and -1-order diffraction light; the second reflected light is vertically incident on the high-reflection mirror 304, returns along the original path, and is split by the second partially transmitting cavity mirror 303. The third transmitted light forms 2-order light of +1-order diffraction light, 0-order diffraction light, and -1-order diffraction light; and so on, forming n-order light of +1-order diffraction light, 0-order diffraction light, and -1-order diffraction light.

[0115] The measuring optical path is initially incident +1 order diffraction light, 0 order diffraction light, -1 order diffraction light from left to right; the three beams of diffraction light are split by the first partially transmitted cavity mirror 306, and the first reflected light returns along the original path to form +1 order diffraction light, 0 order diffraction light and -1 order diffraction light of 0 order light; the first transmitted light is converged by the first focusing lens 307, the 0 order diffraction light is vertically incident on the measuring mirror 8 for reflection, and returns along the original path, the ±1 order diffraction light is incident on the mirror to be measured 8 at opposite and equal angles for reflection, and returns at equal and opposite angles, and is converged by the first focusing lens 307, and is vertically incident on the first partially transmitted cavity mirror 306 for splitting, and the second transmitted light is sequentially from left to right. On the right, the following are formed: -1 order diffraction light, 0 order diffraction light, +1 order diffraction light; the second reflected light returns along the original path, is converged by the first focusing lens 307, 0 order diffraction light is vertically incident on the test mirror 8 for reflection, and returns along the original path. ±1 order diffraction light is incident on the test mirror 8 at opposite and equal angles for reflection, and returns at equal and opposite angles. It is converged by the first focusing lens 307 and vertically incident on the first partially transmitting cavity mirror 306 for splitting. The third transmitted light is formed from left to right: +1 order diffraction light, 0 order diffraction light, -1 order diffraction light; and so on, from left to right, (-1) n n-order light of the first-order diffraction light, n-order light of the 0th-order diffraction light, (-1) n+1 The nth-order light of the first-order diffracted light.

[0116] The method for surface shape measurement using the above-mentioned mirror surface shape measurement system comprises the following steps:

[0117] Step 1: Without installing the test mirror 8 and the high reflective mirror 304, the pulse laser 1 emits a pulse laser;

[0118] Step 2: Adjust the pulse laser 1 so that its emitted pulse laser is horizontally incident on the beam expansion and spectrometer module 2. The beam expansion and spectrometer module 2 divides the pulse laser into mutually parallel 0th order diffraction light and ±1st order diffraction light. Adjust the interference module 3 so that the 0th order diffraction light and the 0th order reflected light of the ±1st order diffraction light can be completely incident on the center of the detection photosensitive surface of the detection module 5 after passing through the interference module 3 and the four-step phase shift module 4, completing the preliminary surface positioning;

[0119] Step 3: Install the high-reflection mirror 304 and adjust the spatial position of the high-reflection mirror 304 so that the spatial positions of the first partially transmissive cavity mirror 306 and the second partially transmissive cavity mirror 303 in the interference module 3 are such that the multi-order light of the 0th-order diffraction light and the multi-order light of the ±1st-order diffraction light formed on the reference light path can be completely incident on the center of the detection photosensitive surface of the detection module 5, thereby completing the precise surface positioning of the reference light path;

[0120] Step 4: Install the mirror to be measured 8 and adjust the spatial position of the mirror to be measured 8 so that the multi-order light of the 0th order diffraction light and the multi-order light of the ±1st order diffraction light formed on the measurement optical path of the interference module 3 are parallel to and coincide with the light formed on the reference optical path, and can be completely incident on the center of the detection photosensitive surface of the detection module 5, thereby completing the precise surface positioning of the measurement optical path;

[0121] Step 5: Repeatedly cross linearly move the mirror 8 to be tested along the horizontal and vertical lines. After each movement, the detection module 5 obtains the 0-level phase shift signal, +1-level phase shift signal and -1-level phase shift signal of the mirror 8 to be tested, and uploads them to the host computer 7 through the receiving module 6. The 0-level phase shift signal is used as a control group, and the ±1-level phase shift signals are calibrated in real time for surface interferometry information.

[0122] The number of movements and the number of movement steps are positively correlated with the size of the mirror 8 to be measured. The larger the mirror size, the more movements are required if the number of movement steps is constant. If the number of movements is constant, the number of movement steps is greater. First, a horizontal linear movement is performed to obtain horizontal linear curve 1. Then, starting from the end point of the horizontal linear movement, a vertical linear nanometer step movement is performed. Then, a horizontal linear movement is performed again to obtain horizontal linear curve 2. This reciprocating cross movement is repeated to obtain multiple horizontal linear curves for the entire surface shape of the mirror 8 according to its size. If the mirror size of the mirror 8 to be measured is 100mm and the number of movement steps is 0.1mm, 1000 movements are required.

[0123] Step 6: The host computer 7 performs phase unwrapping calculation on all acquired 0-level phase shift signals, +1-level phase shift signals, and -1-level phase shift signals, displays multiple sets of linear measurement data, and then uses the multiple sets of linear measurement data to restore the surface information of the mirror to be measured 8.

[0124] Example 2:

[0125] The structure of the mirror surface shape measurement system based on ultrafast high-precision laser scanning of this embodiment is basically the same as that of the mirror surface shape measurement system based on ultrafast high-precision laser scanning of the first embodiment, except that:

[0126] like Figure 5 As shown, the interference module 3 further includes a second focusing lens 309 ; the second focusing lens 309 is arranged on the optical path between the second partially transmitting cavity mirror 303 and the high reflective mirror 304 .

[0127] When the reference optical path includes the second focusing lens 309, the direction of the reference optical path light beam changes, and the direction of the light beam is completely consistent with the measurement optical path. The outgoing pulse lasers from top to bottom are: 0th order light of +1st order diffraction light, 1st order light of -1st order diffraction light, 2nd order light of +1st order diffraction light, 3rd order light of -1st order diffraction light... (-1) n n-order light of the first-order diffraction light; 0-order light of the 0-order diffraction light, 1-order light of the 0-order diffraction light, 2-order light of the 0-order diffraction light, 3-order light of the 0-order diffraction light… n-order light of the 0-order diffraction light; 0-order light of the -1-order diffraction light, 1-order light of the +1-order diffraction light, 2-order light of the -1-order diffraction light, 3-order light of the +1-order diffraction light… (-1) n+1 The nth-order light of the first-order diffracted light.

[0128] The present invention proposes to use ultrashort pulse laser and dual-cavity mirror to perform multiple reflection oscillations to increase the accuracy of surface measurement, and at the same time use the 0th order diffraction light and ±1st order diffraction light of the one-dimensional transmission grating to construct phase decoupling and absolute positioning to realize real-time surface positioning measurement and phase information sequence recognition, thereby realizing ultra-precision mirror surface scanning detection.

[0129] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A mirror surface shape measurement system based on ultrafast high-precision laser scanning, used for measuring the surface shape of a mirror to be measured (8), characterized in that: It comprises a pulse laser (1), a beam expansion and splitting module (2), an interference module (3), a four-step phase shift module (4), a detection module (5), a receiving module (6) and a host computer (7); The pulse laser (1) emits pulse laser; The beam expansion and splitting module (2) splits the pulsed laser into mutually parallel 0th-order diffraction light and ±1st-order diffraction light; The interference module (3) receives the 0th order diffraction light and the ±1st order diffraction light, and causes the three to enter the measurement light path and the reference light path of the interference module (3) respectively for interference, thereby forming multi-order diffraction interference light; the measured mirror (8) is arranged on the measurement light path of the 0th order diffraction light and the ±1st order diffraction light; The four-step phase shift module (4) is used to perform four-step phase shift splitting on the multi-order diffraction interference light to form a phase-shifted light beam; the phase-shifted light beam includes the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 0°, the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 90°, the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 180°, and the 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 270°; The detection module (5) is used to receive the phase-shifted light beam and perform photoelectric conversion to form a 0-level phase-shifted signal, a +1-level phase-shifted signal, and a -1-level phase-shifted signal; The receiving module (6) receives the 0-level phase shift signal, the +1-level phase shift signal and the -1-level phase shift signal respectively, and uploads them to the host computer (7); The host computer (7) is used to perform phase unwrapping calculation on the 0-level phase shift signal, the +1-level phase shift signal and the -1-level phase shift signal, display linear measurement data, and then use the linear measurement data to restore the surface shape information of the mirror to be measured (8).

2. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 1, characterized in that: The pulse laser (1) is an ultrashort pulse laser, which is used to emit 532nm pulse laser with a repetition frequency of 1-1000Hz, a pulse width of 500ps, and a single pulse energy of 1mJ.

3. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 2, characterized in that: The beam expansion and splitting module (2) comprises a first converging lens (201), a beam expansion device (202), a one-dimensional transmission grating (203), a second converging lens (204), and an aperture (205), all of which are located in the optical path of the pulsed laser and are sequentially arranged along the emission direction thereof; The first converging lens (201) is used to make the pulsed laser incident in parallel on the beam expanding device (202); The beam expansion device (202) is used to expand the beam of parallel incident pulsed laser light; The one-dimensional transmission grating (203) is used to form 0th order diffraction light and ±1st order diffraction light; The second converging lens (204) is used to make the 0th order diffracted light and the ±1st order diffracted light respectively incident on the aperture (205) in parallel; The aperture (205) is used to isolate the overlapping portion of the 0th order diffraction light and the ±1st order diffraction light beams, while changing the energy level and the aperture size of the incident light spot.

4. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 1, 2 or 3, characterized in that: The interference module (3) comprises a first polarization beam splitting prism (301) provided with four sides, wherein the first side is opposite to the third side, and the second side is opposite to the fourth side; The first side corresponds to the aperture (205) and is used to receive the 0th order diffraction light and the ±1st order diffraction light; The second side corresponds to the four-step phase shift module (4), and a half-wave plate (308) is provided on the optical path between the second side and the four-step phase shift module (4) for emitting multi-order diffraction interference light; The third side is provided with a second quarter-wave plate (302), a second partially transmitting cavity mirror (303), and a high-reflection mirror (304) in sequence along a direction away from the third side, forming a reference optical path; The fourth side is provided with a first quarter-wave plate (305), a first partially transmissive cavity mirror (306), and a first focusing lens (307) in sequence along a direction away from the fourth side; a side of the first focusing lens (307) away from the first partially transmissive cavity mirror (306) is used to provide a mirror to be measured (8); the first quarter-wave plate (305), the first partially transmissive cavity mirror (306), the first focusing lens (307), and the mirror to be measured (8) constitute a measurement optical path; The first partially transmissive cavity mirror (306) and the second partially transmissive cavity mirror (303) are both double cavity mirrors, and the sides of the two mirrors close to the first polarization beam splitting prism (301) are coated with a reflective film and the other sides are coated with an anti-reflection film, the reflectivity of the reflective film is ≥90%, and the transmittance of the anti-reflection film is ≥90%. The beam splitting surface of the first polarization beam splitting prism (301) is equidistant from the rear surfaces of the first partially transmissive cavity mirror (306) and the second partially transmissive cavity mirror (303); the distance from the rear surface of the first partially transmissive cavity mirror (306) to the reflective surface of the test mirror (8) is equidistant from the distance from the rear surface of the second partially transmissive cavity mirror (303) to the reflective surface of the high reflective mirror (304); and the rear surface is a surface away from the first polarization beam splitting prism (301).

5. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 4, characterized in that: The four-step phase shift module (4) comprises a beam splitter prism (401), a second polarization beam splitter prism (404), and a third polarization beam splitter prism (405); The beam splitter prism (401) is used to perform energy splitting on the multi-order diffraction interference light emitted by the half-wave plate (308) to form reflected light and transmitted light; the beam splitter prism (401) has a splitting ratio of 5:5; The second polarization beam splitter prism (404) is located on the optical path of the transmitted light, and a third quarter-wave plate (402) is provided on the optical path between the second polarization beam splitter prism (404) and the beam splitter prism (401) for performing polarization beam splitting on the transmitted light to form 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 90°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 270°; The third polarization beam splitter prism (405) is located on the optical path of the reflected light, and a fourth quarter-wave plate (403) is provided on the optical path between the third polarization beam splitter prism (405) and the beam splitter prism (401) for performing polarization beam splitting on the reflected light to form 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 0°, and 0th order diffraction interference light and ±1st order diffraction interference light with a phase of 180°.

6. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 5, characterized in that: The polarization angles of the first quarter wave plate (305), the second quarter wave plate (302), the third quarter wave plate (402), and the fourth quarter wave plate (403) are all 45°.

7. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 6, characterized in that: The detection module (5) includes first to twelfth photodetectors; The first photodetector (501) is used to receive the 0th order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first 0th order phase shift signal; The second photodetector (502) is used to receive the 0th order diffraction interference light with a phase of 180 degrees and perform photoelectric conversion to form a second 0th order phase shift signal; The third photodetector (503) is used to receive the 0th order diffraction interference light with a phase of 90 degrees and perform photoelectric conversion to form a third 0th order phase shift signal; The fourth photodetector (504) is used to receive the 0th order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth 0th order phase shift signal; The fifth photodetector (505) is used to receive the +1st order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first +1st order phase shift signal; The sixth photodetector (506) is used to receive the +1st order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second +1st order phase shift signal; The seventh photodetector (507) is used to receive the +1st order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a third +1st order phase shift signal; The eighth photodetector (508) is used to receive the +1st order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth +1st order phase shift signal; The ninth photodetector (509) is used to receive the -1st order diffraction interference light with a phase of 0° and perform photoelectric conversion to form a first -1st order phase shift signal; The tenth photodetector (510) is used to receive the -1st order diffraction interference light with a phase of 180° and perform photoelectric conversion to form a second -1st order phase shift signal; The eleventh photodetector (511) is used to receive the -1st order diffraction interference light with a phase of 90° and perform photoelectric conversion to form a third -1st order phase shift signal; The twelfth photodetector (512) is used to receive the -1st order diffraction interference light with a phase of 270° and perform photoelectric conversion to form a fourth -1st order phase shift signal; The first to fourth 0-level phase-shifted signals are the 0-level phase-shifted signals; the first to fourth +1-level phase-shifted signals are the +1-level phase-shifted signals; and the first to fourth -1-level phase-shifted signals are -1-level phase-shifted signals.

8. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 7, characterized in that: The receiving module (6) includes a first oscilloscope (601), a second oscilloscope (602) and a third oscilloscope (603); The first oscilloscope (601) is used to receive a level 0 phase shift signal and upload it to a host computer (7); The second oscilloscope (602) is used to receive the +1-level phase shift signal and upload it to the host computer (7); The third oscilloscope (603) is used to receive the -1 level phase shift signal and upload it to the host computer (7).

9. The mirror surface measurement system based on ultrafast high-precision laser scanning according to claim 7, characterized in that: The interference module (3) further includes a second focusing lens (309); The second focusing lens (309) is arranged on the optical path between the second partially transmitting cavity mirror (303) and the high reflective mirror (304).

10. A mirror surface shape measurement method based on ultrafast high-precision laser scanning, using the mirror surface shape measurement system based on ultrafast high-precision laser scanning according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Without installing the test mirror (8) and the high reflective mirror (304), the pulse laser (1) emits pulse laser light; Step 2: Adjust the pulse laser (1) so that the pulse laser emitted by it is horizontally incident on the beam expansion and splitting module (2). The beam expansion and splitting module (2) splits the pulse laser into mutually parallel 0th order diffraction light and ±1st order diffraction light. Adjust the interference module (3) so that the 0th order diffraction light and the 0th order reflected light of the ±1st order diffraction light can be completely incident on the center of the detection photosensitive surface of the detection module (5) after passing through the interference module (3) and the four-step phase shift module (4), thereby completing the preliminary surface positioning. Step 3: Install the high reflective mirror (304), and adjust the spatial position of the high reflective mirror (304) so ​​that the multi-order light of the 0th order diffraction light and the multi-order light of the ±1st order diffraction light formed on the reference light path of the interference module (3) can be completely incident on the center of the detection photosensitive surface of the detection module (5), thereby completing the precise surface positioning of the reference light path; Step 4: Install the mirror to be measured (8), and adjust the spatial position of the mirror to be measured (8) so that the multi-order light of the 0th order diffraction light and the multi-order light of the ±1st order diffraction light formed on the measurement light path of the interference module (3) are parallel to and overlap with the light formed on the reference light path, and can be completely incident on the center of the detection photosensitive surface of the detection module (5), thereby completing the precise surface positioning of the measurement light path; Step 5, repeatedly cross-linearly moving the mirror to be measured (8) along the horizontal line and the vertical line, after each movement, the detection module (5) obtains the 0-level phase shift signal, the +1-level phase shift signal and the -1-level phase shift signal of the mirror to be measured (8), and uploads them to the host computer (7) through the receiving module (6), wherein the 0-level phase shift signal is used as a control group, and the ±1-level phase shift signals are calibrated in real time for surface interferometry information; Step 6: The host computer (7) performs phase unwrapping calculation on all acquired 0-level phase shift signals, +1-level phase shift signals and -1-level phase shift signals, displays multiple sets of linear measurement data, and then uses the multiple sets of linear measurement data to restore the surface information of the mirror to be measured (8).

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