Optical element angle measuring device

Abstract

The application relates to an optical element angle measuring device, which comprises a laser light source, a first light splitter, a second light splitter, a folding mirror, a first differential measurement component, an environment compensation component, a second differential measurement component and a data processing device, the laser light source is used for emitting laser light, the laser light is divided into three paths by the first light splitter, the second light splitter and the folding mirror, two of the three paths are reflected back to the first differential measurement component and the second differential measurement component after passing through the first differential measurement component and the second differential measurement component respectively, the first differential measurement component and the second differential measurement component obtain a first differential measurement signal and a second differential measurement signal according to the reflected light, the remaining one of the three paths is received by the environment compensation component, the environment compensation component obtains an environment compensation signal according to the remaining one, and the data processing device calculates an angle change value of the optical element according to the first differential measurement signal, the second differential measurement signal and the environment compensation signal.

Description

Technical Field

[0001] This invention relates to the field of optical precision measurement technology, and more specifically to an optical element angle measuring device. Background Technology

[0002] Synchrotron radiation is electromagnetic waves emitted tangentially when charged particles (such as electrons) moving at near-light speed change direction in a magnetic field. It is characterized by high brightness, a wide spectrum (covering infrared to hard X-rays), high collimation, and a specific pulse time structure. Hard X-ray free-electron lasers, on the other hand, utilize high-energy electron beams passed through an undulator to generate coherent X-rays. Their brightness is billions of times higher than synchrotron radiation, and they possess ultrashort pulses (femtosecond levels) and ultra-high peak power (10²). 0 With their respective advantages (W / cm²), both have irreplaceable application value in cutting-edge scientific research, advanced manufacturing, and other fields.

[0003] The beamline is a crucial core component in synchrotron radiation sources and free-electron laser devices, used for transmitting, controlling, and focusing the beam. It mainly consists of optical elements such as monochromators, collimating mirrors, focusing mirrors, and deflecting mirrors. During actual operation of the beamline, various factors, including ground vibration, liquid nitrogen turbulence, thermal imbalance of the mirror body or crystal, and micro-vibrations of the motion adjustment mechanism, can significantly interfere with the stability of the angles (pitch angle, roll angle, yaw angle) of the key optical elements of the beamline. This, in turn, affects the positional stability of the focused spot and the stability of the output energy and luminous flux during energy scanning.

[0004] With the continuous development of synchrotron radiation and free-electron laser technologies, the requirements for the angular accuracy of optical components in beamline equipment are becoming increasingly stringent. In X-ray diffraction experiments, the angular stability of optical components needs to reach the sub-microradian (μrad) level to ensure accurate resolution of crystal structures. In hard X-ray free-electron laser beamlines, the attitude angular resolution requirement for key optical components has reached 20 nrad, and the angular stability requirement is 50 nrad / 10 min. Therefore, developing high-precision and high-stability optical component angle measurement technology has become a key technical problem that urgently needs to be solved in the field of synchrotron radiation and free-electron lasers. Summary of the Invention

[0005] The purpose of this invention is to provide an optical element angle measuring device to achieve high-precision and high-stability optical element angle measurement.

[0006] To achieve the above objectives, the present invention provides an optical element angle measuring device, comprising a laser source, a first beam splitter, a second beam splitter, a folding mirror, a first differential measurement component, an environmental compensation component, a second differential measurement component, and a data processing device. The laser source, the first beam splitter, the second beam splitter, and the folding mirror are sequentially arranged along a first optical path. The laser source emits laser light, which is incident on the first beam splitter along the first optical path and split into a first beam propagating along the first optical path and a second beam propagating along a second optical path. The first beam is incident on the second beam splitter and split into a third beam propagating along the first optical path and a fourth beam propagating along the third optical path. The third beam is reflected by the folding mirror to form a fifth beam propagating along the fourth optical path. The optical axes of the second, third, and fourth optical paths are parallel to each other and perpendicular to the reflecting surface of the optical element.

[0007] The first differential measurement component is located in the second optical path. After the second beam passes through the first differential measurement component, it is reflected back to the first differential measurement component by the reflective surface of the optical element. The first differential measurement component obtains a first differential measurement signal based on the second beam and its reflected light. The second differential measurement component is located in the fourth optical path. After the fifth beam passes through the second differential measurement component, it is reflected back to the second differential measurement component by the reflective surface of the optical element. The second differential measurement component obtains a second differential measurement signal based on the fifth beam and its reflected light. The environmental compensation component is located in the third optical path. The environmental compensation component is used to receive the fourth beam and obtain an environmental compensation signal based on the fourth beam. The data processing device is connected to the first differential measurement component, the second differential measurement component, and the environmental compensation component, respectively, and is used to calculate the angle change value of the optical element based on the first differential measurement signal, the second differential measurement signal, and the environmental compensation signal.

[0008] Optionally, the ratio of transmittance to reflectance of the first beam splitter is 2:1, and the ratio of transmittance to reflectance of the second beam splitter is 1:1.

[0009] Optionally, the laser source is a dual-frequency laser source.

[0010] Optionally, the first differential measurement component includes a first differential interferometer, a first reference mirror, a first fiber optic receiver, and a first signal processor. The second beam is incident on the first differential interferometer and split into two reference beams and two measurement beams. The two reference beams are transmitted to the first reference mirror and then reflected back to the first differential interferometer. The two measurement beams pass through the through-hole on the first reference mirror and then illuminate the reflective surface of the optical element and are reflected back to the first differential interferometer. The two reference beams and two measurement beams that are reflected back interfere with each other at the first differential interferometer, generating an interference signal. The first fiber optic receiver is used to couple the interference signal into the optical fiber and transmit it to the first signal processor. The first signal processor is used to convert the interference signal into an electrical signal and analyze the electrical signal to obtain the first differential measurement signal.

[0011] The second differential measurement component includes a second differential interferometer, a second reference mirror, a second fiber optic receiver, and a second signal processor. The fifth beam is incident on the second differential interferometer and split into two reference beams and two measurement beams. The two reference beams are transmitted to the second reference mirror and reflected back to the second differential interferometer. The two measurement beams pass through the through-hole on the second reference mirror and illuminate the reflective surface of the optical element and are reflected back to the second differential interferometer. The two reference beams and two measurement beams that are reflected back interfere with each other at the second differential interferometer, generating an interference signal. The second fiber optic receiver is used to couple the interference signal into the optical fiber and transmit it to the second signal processor. The second signal processor is used to convert the interference signal into an electrical signal and analyze the electrical signal to obtain the second differential measurement signal.

[0012] Optionally, the environmental compensation component includes a third differential interferometer, a zero-expansion cavity, a third fiber optic receiver, and a third signal processor. The zero-expansion cavity has a front surface and a rear surface. After the fourth beam is incident on the third differential interferometer, it is split into two reference beams and two measurement beams. The two reference beams are reflected back to the third differential interferometer by the front surface. The two measurement beams pass through a preset hole on the front surface and then illuminate the rear surface, and are reflected back to the third differential interferometer by the rear surface. The two reflected reference beams and two measurement beams interfere with each other in the third differential interferometer to generate interference signals. The third fiber optic receiver is used to couple the interference signals into an optical fiber and transmit them to the third signal processor. The third signal processor is used to convert the interference signals into electrical signals and resolve them into environmental compensation signals.

[0013] Optionally, calculating the angle change value of the optical element based on the first differential measurement signal, the second differential measurement signal, and the environmental compensation signal specifically includes:

[0014] The first differential measurement signal is corrected using the environmental compensation signal to obtain the corrected first differential measurement signal;

[0015] The second differential measurement signal is corrected using the environmental compensation signal to obtain the corrected second differential measurement signal;

[0016] The angle change value of the optical element is calculated based on the corrected first differential measurement signal and the corrected second differential measurement signal.

[0017] Optionally, the corrected first differential measurement signal satisfies the following relationship:

[0018] ΔL1=L1+ΔL1',

[0019] ΔL1'=ΔL-k×H1×ΔL,

[0020] Wherein, ΔL1 is the corrected first measurement signal, L1 is the first differential measurement signal, ΔL1' is the first correction amount, ΔL is the environmental compensation signal, k is the pre-calibrated environmental refractive index gradient coefficient, and H1 is the distance between the optical axes of the second and third optical paths.

[0021] The corrected second differential measurement signal satisfies the following relationship:

[0022] ΔL2=L2+ΔL2',

[0023] ΔL2'=ΔL+k×H2×ΔL,

[0024] Wherein, ΔL2 is the corrected second differential measurement signal, L2 is the second differential measurement signal, ΔL2' is the second correction amount, and H2 is the distance between the optical axes of the third and fourth optical paths;

[0025] The angular change value of the optical element satisfies the following relationship:

[0026] θ = |ΔL1 - ΔL2| / H

[0027] Wherein, θ is the angular change value of the optical element, and H is the distance between the optical axes of the second optical path and the fourth optical path.

[0028] Optionally, it also includes an active vibration isolation base, wherein the laser light source, the first beam splitter, the second beam splitter, the folding mirror, the first differential measurement component, the environmental compensation component, and the second differential measurement component are all disposed on the active vibration isolation base.

[0029] Optionally, the system also includes a first sliding platform, a second sliding platform, a third sliding platform, and a guide rail, to adapt to the size of the optical component under test and maintain the optical path's beam splitting and collimation characteristics unchanged, thereby improving its versatility and convenience. The guide rail is mounted on the active vibration isolation base. The first, second, and third sliding platforms are all slidably mounted on the guide rail. The first beam splitter and the first differential measurement component are mounted on the first sliding platform, the second beam splitter and the environmental compensation component are mounted on the second sliding platform, and the folding mirror and the second differential measurement component are mounted on the third sliding platform.

[0030] Optionally, the system further includes a rotating mechanism, which comprises a first fixed seat and a second fixed seat. The first fixed seat and the second fixed seat are spaced apart on the active vibration isolation base. One end of the guide rail is rotatably connected to the first fixed seat, and the other end of the guide rail is slidably disposed on the second fixed seat. The second fixed seat is provided with a first push rod and a second push rod, which are arranged opposite to each other and located on both sides of the guide rail, respectively. These push rods are used to push the guide rail to rotate in a direction away from or close to the optical element, so that it can follow the angular movement of the optical element, expand the angle measurement range, break through the angle tolerance limit of interference angle measurement, and minimize the cosine error. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of an optical element angle measuring device according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of the first differential measurement component of the optical element angle measuring device according to an embodiment of the present invention. Detailed Implementation

[0033] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0034] like Figure 1As shown, this embodiment of the invention provides an optical element angle measuring device, which includes a laser source 100, a first beam splitter 200, a second beam splitter 300, a folding mirror 400, a first differential measurement component 500, an environmental compensation component 600, a second differential measurement component 700, and a data processing device 800. The laser source 100, the first beam splitter 200, and the second beam splitter 300 are arranged sequentially along a first optical path. The laser source 100 is used to emit laser light, which is incident on the first beam splitter 200 along the first optical path and passes through the second beam splitter 300. A beam splitter 200 splits a first beam propagating along a first optical path and a second beam propagating along a second optical path. The first beam is incident on a second beam splitter 300 and splits into a third beam propagating along the first optical path and a fourth beam propagating along the third optical path. The third beam is incident on a folding mirror 400 and folded by the folding mirror 400 to form a fifth beam propagating along the fourth optical path. The optical axes of the second, third, and fourth optical paths are parallel to each other and all perpendicular to the reflecting surface of the optical element 900. The first differential measurement assembly 5... A second beam is positioned on the second optical path. After passing through the first differential measurement component 500, the second beam illuminates the reflective surface of the optical element 900 and is reflected back to the first differential measurement component 500. The first differential measurement component 500 obtains a first differential measurement signal based on the second beam and the reflected light of the second beam. An environmental compensation component 600 is positioned on the third optical path. The fourth beam is received by the environmental compensation component 600, and the environmental compensation component 600 obtains an environmental compensation signal based on the fourth beam. A second differential measurement component 700 is positioned on the fourth optical path. After passing through the second differential measurement component 700, the fifth beam illuminates the reflective surface of the optical element 900 and is reflected back to the second differential measurement component 700. The second differential measurement component 700 obtains a second differential measurement signal based on the fifth beam and the reflected light of the fifth beam. A data processing device 800 receives the first differential measurement signal, the second differential measurement signal, and the environmental compensation signal, and calculates the angle change value of the optical element 900 based on these three signals.

[0035] The laser source 100 can be a dual-frequency laser source, which can output a wavelength-stable monochromatic laser to provide the first differential measurement component 500, the environmental compensation component 600 and the second differential measurement component 700 with the same source of incident light.

[0036] The first beam splitter 200 can be a 33% beam splitter with a transmittance to reflectance ratio of approximately 2:1. Thus, the intensity ratio of the first beam to the second beam is 2:1, with the intensity of the first beam being approximately 2 / 3 of that of the laser beam and the intensity of the second beam approximately 1 / 3 of the laser beam. The second beam splitter 300 can be a 50% beam splitter with a transmittance to reflectance ratio of 1:1. Thus, the intensity of the third and fourth beams is both 1 / 2 of the intensity of the first beam, which is 1 / 3 of the laser beam. The fifth beam is the reflected light from the third beam, and its intensity is approximately equal to that of the third beam; therefore, the intensity of the fifth beam is approximately 1 / 3 of that of the laser beam. In other words, the intensity of the second, fourth, and fifth beams obtained through the first beam splitter 200, the second beam splitter 300, and the folding mirror 400 is essentially the same.

[0037] The first differential measurement component 500 and the second differential measurement component 700 have the same structure, thus forming two completely symmetrical measurement optical paths. For example... Figure 2As shown, the first differential measurement assembly 500 includes a first differential interferometer 510, a first reference mirror 520, a first fiber optic receiver 530, and a first signal processor 540. The second beam, split by the first beam splitter 200, is incident on the first differential interferometer 510 and split into two reference beams and two measurement beams. The two reference beams are transmitted to the first reference mirror 520, reflected by the first reference mirror 520, and return to the first differential interferometer 510. The two measurement beams pass through the first reference mirror 520 and illuminate the reflective surface of the optical element 900, and are then reflected by the optical element 900. The reflected light returns to the first differential interferometer 510. The first reference mirror 520 may have two through holes 521 for the two measurement beams to pass through. The two reference beams and two measurement beams that are reflected back interfere at the first differential interferometer 510, generating interference signals. The first fiber optic receiver 530 couples the interference signals into the optical fiber and transmits them to the first signal processor 540. The first signal processor 540 converts the interference signals into electrical signals and resolves them into displacement signals of the optical element 900 relative to the first differential interferometer 510 (i.e., the first differential measurement signal). Similar to the first differential measurement assembly 500, the second differential measurement assembly 700 includes a second differential interferometer 710, a second reference mirror 720, a second fiber optic receiver 730, and a second signal processor 740. A fifth beam is incident on the second differential interferometer 710 and split into two reference beams and two measurement beams. The two reference beams are transmitted to the second reference mirror 720 and reflected back to the second differential interferometer 710. The two measurement beams pass through the second reference mirror 720 and illuminate the reflecting surface of the optical element 900, and are reflected by the reflecting surface of the optical element 900. After the beams are reflected back to the second differential interferometer 710, the second reference mirror 720 may be provided with two through holes for the two measurement beams to pass through. The two reference beams and the two measurement beams that are reflected back interfere at the second differential interferometer 710 respectively, generating interference signals. The second fiber optic receiver 730 couples the interference signals into the fiber and transmits them to the second signal processor 740. The second signal processor 740 is used to convert the interference signals into electrical signals and resolve them into displacement signals of the optical element 900 relative to the second differential interferometer 710 (i.e., the second differential measurement signal).

[0038] The environmental compensation component 600 may include a third differential interferometer 610, a zero-expansion cavity 620, a third fiber optic receiver 630, and a third signal processor 640. A fourth beam is incident on the third differential interferometer 610 and split into two reference beams and two measurement beams. The zero-expansion cavity 620 has a front surface and a rear surface. An aperture is provided on the front surface for the two measurement beams to pass through. The two reference beams are reflected back to the third differential interferometer 610 by the front surface, while the two measurement beams pass through the aperture, are reflected back to the third differential interferometer 610 by the rear surface. The two reference beams and two measurement beams reflected back to the third differential interferometer 610 interfere with each other, generating interference signals. The third fiber optic receiver 630 couples the interference signals into an optical fiber and transmits them to the third signal processor 640. The third signal processor 640 converts the interference signals into electrical signals and resolves them into reference signals (i.e., environmental compensation signals). The environmental compensation signals reflect changes in the environmental refractive index and can be used for real-time compensation of the two measurement signals.

[0039] The first differential interferometer 510, the second differential interferometer 710, and the third differential interferometer 610 are a group of mirrors used to realize differential interferometry. They are usually composed of multiple mirrors, and their structure is well known in the art and will not be described in detail here.

[0040] The data processing device 800 is connected to the first signal processor 540, the second signal processor 740 and the third signal processor 640 respectively to receive the first differential measurement signal, the second differential measurement signal and the environmental compensation signal.

[0041] The data processing device 800 calculates the angle change value of the optical element 900 based on the first differential measurement signal, the second differential measurement signal, and the environmental compensation signal as follows:

[0042] Assuming the environmental compensation signal is ΔL, the first differential measurement signal is L1, the second differential measurement signal is L2, H is the distance between the optical axes of the second and fourth optical paths, H1 is the distance between the optical axes of the second and third optical paths, and H2 is the distance between the optical axes of the third and fourth optical paths, the data processing device 800 first compares the first and second differential measurement signals with the environmental compensation signal to correct the error caused by the fluctuation of the environmental refractive index. The corrected first differential measurement signal is ΔL1, ΔL1=L1+ΔL1', and the corrected second differential measurement signal is ΔL2, ΔL2=L2+ΔL2', where the first correction amount ΔL1'=ΔL-k×H1×ΔL, and the second correction amount ΔL2'=ΔL+k×H2×ΔL, where k is the pre-calibrated environmental refractive index gradient coefficient. Then, based on the corrected first and second differential measurement signals and H, the angle change value θ of the optical element 900 is calculated, θ=|ΔL1-ΔL2| / H.

[0043] The calibration method for the environmental refractive index gradient coefficient is as follows:

[0044] Keeping the first sliding platform fixed, the value of H1 is changed by moving the third sliding platform, thereby obtaining multiple values ​​of H1. Under each H1, the environmental compensation signal ΔL under that H1 is obtained. Then, the curve ΔL-H1 is obtained by linear fitting of each H1 and the corresponding ΔL, and its slope is k.

[0045] When actually measuring an angle, the value of H is related to the size of the optical element 900. Based on the specific size of the optical element 900, the corresponding H can be determined to achieve the optimal measurement resolution. For example, H can be obtained by subtracting the measurement spot diameter from the total length of the optical element 900, and then subtracting the edge chamfers and other parts of the optical element 900.

[0046] The optical element angle measurement device may further include an active vibration isolation base 1000, a laser light source 100, a first beam splitter 200, a second beam splitter 300, a folding mirror 400, a first differential measurement component 500, an environmental compensation component 600, and a second differential measurement component 700, all mounted on the active vibration isolation base 1000 to effectively reduce the impact of vibration on the measurement results. With the active vibration isolation base 1000 applied, the measurement error caused by vibration can be largely ignored, enabling absolute angle measurement.

[0047] The optical element angle measuring device may further include a first sliding platform 1100, a second sliding platform 1200, a third sliding platform 1300, and a guide rail 1400. The guide rail 1400 is mounted on the active vibration isolation base 1000. The first sliding platform 1100, the second sliding platform 1200, and the third sliding platform 1300 are all slidably mounted on the guide rail 1400, and are arranged alternately in sequence. All three can slide on the guide rail 1400. The first beam splitter 200 and the first differential measurement component 500 are mounted on the first sliding platform 1100. The second beam splitter 300 and the environmental compensation component 600 are mounted on the second sliding platform 1200. The folding mirror 400 and the second differential measurement component 700 are mounted on the third sliding platform 1300. By sliding each sliding platform on the guide rail 1400, the distance between the optical axes of any two of the second, third, and fourth optical paths can be adjusted.

[0048] In some embodiments, the first signal processor 540, the second signal processor 740, and the third signal processor 640 may not be disposed on each sliding platform, but rather all may be disposed on the active vibration isolation base 1000, such as... Figure 1 As shown. Alternatively, each signal processor can be located outside the active vibration isolation base 1000.

[0049] The optical element angle measuring device may further include a rotating mechanism, on which a guide rail 1400 is mounted. The rotating mechanism is used to rotate the guide rail 1400, thereby adjusting the angles between the second, third, and fourth optical paths and the reflecting surface of the optical element 900, so that the optical axes of the second, third, and fourth optical paths are perpendicularly aligned with the reflecting surface of the optical element 900. Specifically, as shown... Figure 1 As shown, the rotating mechanism may include a first fixed base 1500 and a second fixed base 1600, which are spaced apart on the active vibration isolation base 1000. One end of the guide rail 1400 is rotatably connected to the first fixed base 1500, for example, the two can be connected by means of a guide rail along the guide rail 1400. Figure 1 A rotating shaft extending perpendicular to the plane of the paper is rotatably connected to the guide rail 1400, and the other end of the guide rail 1400 is slidably mounted on the second fixed base 1600. The second fixed base 1600 is provided with a first push rod 1610 and a second push rod 1620. The first push rod 1610 and the second push rod 1620 are arranged opposite each other and are located on both sides of the guide rail 1400. Both the first push rod 1610 and the second push rod 1620 can move relative to the second fixed base 1600 to approach or move away from the guide rail 1400. When the first push rod 1610 moves toward the guide rail 1400, the first push rod 1610 can gradually approach the guide rail 1400 and push the guide rail 1400 to rotate around the rotating shaft toward the direction away from the optical element 900. When the second push rod 1620 moves toward the guide rail 1400, the second push rod 1620 can gradually approach the guide rail 1400 and push the guide rail 1400 to rotate around the rotating shaft toward the direction closer to the optical element 900. This allows for the vertical alignment of the optical axes of the second, third, and fourth optical paths with the optical element 900. During adjustment, the pinhole aperture method can be used to determine if the alignment is perpendicular.

[0050] The optical element angle measuring device of this invention has a working spacing (i.e., the distance between the measuring component and the reflecting surface of the optical element 900) that can reach the working limit of a dual-frequency laser interferometer (typically 40 meters), fully covering the measurement needs of beamline equipment and thus having a wider range of applications. Both the first differential measuring component 500 and the second differential measuring component 700 employ differential interferometry, providing two interference signals. Since environmental vibrations, temperature fluctuations, and other noises have similar effects on the two interference signals, the noise is canceled out after differential processing, greatly improving the resistance to environmental disturbances. The theoretical angle resolution of this invention can reach 0.2 nrad, meeting the requirements for high-precision and high-stability angle measurement. Requirements: By sliding each sliding platform along the guide rail 1400, the distance between the optical axes of the second and fourth optical paths can be adjusted, thus adapting to the angle measurement of optical elements 900 of different sizes, while maintaining the spectral splitting and collimation characteristics of the two optical paths unchanged. This eliminates the need to readjust the collimation of the optical paths when applying to different measurement objects, improving the versatility and convenience of use. Furthermore, by rotating the mechanism, the angle between the optical axes of the second to fourth optical paths and the reflecting surface of the optical element 900 can be adjusted, adapting to the angular position of the optical element 900. This expands the angle measurement range to accommodate any optical element 900, breaking through the angle tolerance limitations of interference angle measurement and minimizing cosine errors.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. An optical element angle measuring device, characterized in that, The system includes a laser source, a first beam splitter, a second beam splitter, a folding mirror, a first differential measurement component, an environmental compensation component, a second differential measurement component, and a data processing device. The laser source, the first beam splitter, the second beam splitter, and the folding mirror are arranged sequentially along a first optical path. The laser source emits laser light. The laser light is incident on the first beam splitter along the first optical path and split into a first beam traveling along the first optical path and a second beam traveling along a second optical path. The first beam is incident on the second beam splitter and split into a third beam traveling along the first optical path and a fourth beam traveling along the third optical path. The third beam is reflected by the folding mirror to form a fifth beam traveling along the fourth optical path. The optical axes of the second, third, and fourth optical paths are parallel to each other and perpendicular to the reflecting surface of the optical element. The first differential measurement component is located in the second optical path. After the second beam passes through the first differential measurement component, it is reflected back to the first differential measurement component by the reflective surface of the optical element. The first differential measurement component obtains a first differential measurement signal based on the second beam and its reflected light. The second differential measurement component is located in the fourth optical path. After the fifth beam passes through the second differential measurement component, it is reflected back to the second differential measurement component by the reflective surface of the optical element. The second differential measurement component obtains a second differential measurement signal based on the fifth beam and its reflected light. The environmental compensation component is located in the third optical path. The environmental compensation component is used to receive the fourth beam and obtain an environmental compensation signal based on the fourth beam. The data processing device is connected to the first differential measurement component, the second differential measurement component, and the environmental compensation component, respectively, and is used to calculate the angle change value of the optical element based on the first differential measurement signal, the second differential measurement signal, and the environmental compensation signal.

2. The optical element angle measuring device according to claim 1, characterized in that, The ratio of transmittance to reflectance of the first beam splitter is 2:1, and the ratio of transmittance to reflectance of the second beam splitter is 1:

1.

3. The optical element angle measuring device according to claim 1, characterized in that, The laser source is a dual-frequency laser source.

4. The optical element angle measuring device according to claim 1, characterized in that, The first differential measurement component includes a first differential interferometer, a first reference mirror, a first fiber optic receiver, and a first signal processor. The second beam is incident on the first differential interferometer and split into two reference beams and two measurement beams. The two reference beams are transmitted to the first reference mirror and then reflected back to the first differential interferometer. The two measurement beams pass through the through-hole on the first reference mirror and then illuminate the reflective surface of the optical element and are reflected back to the first differential interferometer. The two reference beams and two measurement beams that are reflected back interfere with each other at the first differential interferometer, generating an interference signal. The first fiber optic receiver is used to couple the interference signal into the optical fiber and transmit it to the first signal processor. The first signal processor is used to convert the interference signal into an electrical signal and analyze the electrical signal to obtain the first differential measurement signal. The second differential measurement component includes a second differential interferometer, a second reference mirror, a second fiber optic receiver, and a second signal processor. The fifth beam is incident on the second differential interferometer and split into two reference beams and two measurement beams. The two reference beams are transmitted to the second reference mirror and reflected back to the second differential interferometer. The two measurement beams pass through the through-hole on the second reference mirror and illuminate the reflective surface of the optical element and are reflected back to the second differential interferometer. The two reference beams and two measurement beams that are reflected back interfere with each other at the second differential interferometer, generating an interference signal. The second fiber optic receiver is used to couple the interference signal into the optical fiber and transmit it to the second signal processor. The second signal processor is used to convert the interference signal into an electrical signal and analyze the electrical signal to obtain the second differential measurement signal.

5. The optical element angle measuring device according to claim 1, characterized in that, The environmental compensation component includes a third differential interferometer, a zero-expansion cavity, a third fiber optic receiver, and a third signal processor. The zero-expansion cavity has a front surface and a rear surface. After the fourth beam is incident on the third differential interferometer, it is split into two reference beams and two measurement beams. The two reference beams are reflected back to the third differential interferometer by the front surface. The two measurement beams pass through a preset hole on the front surface and then illuminate the rear surface, where they are reflected back to the third differential interferometer. The reflected reference beams and two measurement beams interfere with each other in the third differential interferometer, generating interference signals. The third fiber optic receiver couples the interference signals into an optical fiber and transmits them to the third signal processor. The third signal processor converts the interference signals into electrical signals and resolves them into environmental compensation signals.

6. The optical element angle measuring device according to claim 1, characterized in that, The angle change value of the optical element is calculated based on the first differential measurement signal, the second differential measurement signal, and the environmental compensation signal, specifically including: The first differential measurement signal is corrected using the environmental compensation signal to obtain the corrected first differential measurement signal; The second differential measurement signal is corrected using the environmental compensation signal to obtain the corrected second differential measurement signal; The angle change value of the optical element is calculated based on the corrected first differential measurement signal and the corrected second differential measurement signal.

7. The optical element angle measuring device according to claim 6, characterized in that, The corrected first differential measurement signal satisfies the following relationship: ΔL1=L1+ΔL1', ΔL1'=ΔL-k×H1×ΔL, Wherein, ΔL1 is the corrected first measurement signal, L1 is the first differential measurement signal, ΔL1' is the first correction amount, ΔL is the environmental compensation signal, k is the pre-calibrated environmental refractive index gradient coefficient, and H1 is the distance between the optical axes of the second and third optical paths. The corrected second differential measurement signal satisfies the following relationship: ΔL2=L2+ΔL2', ΔL2'=ΔL+k×H2×ΔL, Wherein, ΔL2 is the corrected second differential measurement signal, L2 is the second differential measurement signal, ΔL2' is the second correction amount, and H2 is the distance between the optical axes of the third and fourth optical paths; The angular change value of the optical element satisfies the following relationship: θ = |ΔL1 - ΔL2| / H Wherein, θ is the angular change value of the optical element, and H is the distance between the optical axes of the second optical path and the fourth optical path.

8. The optical element angle measuring device according to claim 1, characterized in that, It also includes an active vibration isolation base, on which the laser light source, the first beam splitter, the second beam splitter, the folding mirror, the first differential measurement component, the environmental compensation component, and the second differential measurement component are all mounted.

9. The optical element angle measuring device according to claim 8, characterized in that, It also includes a first sliding platform, a second sliding platform, a third sliding platform, and a guide rail. The guide rail is mounted on the active vibration isolation base. The first sliding platform, the second sliding platform, and the third sliding platform are all slidably mounted on the guide rail. The first beam splitter and the first differential measurement component are mounted on the first sliding platform. The second beam splitter and the environmental compensation component are mounted on the second sliding platform. The folding mirror and the second differential measurement component are mounted on the third sliding platform.

10. The optical element angle measuring device according to claim 9, characterized in that, It also includes a rotating mechanism, which includes a first fixed seat and a second fixed seat. The first fixed seat and the second fixed seat are spaced apart on the active vibration isolation base. One end of the guide rail is rotatably connected to the first fixed seat, and the other end of the guide rail is slidably disposed on the second fixed seat. The second fixed seat is provided with a first push rod and a second push rod. The first push rod and the second push rod are arranged opposite to each other and are respectively located on both sides of the guide rail, for pushing the guide rail to rotate in a direction away from or closer to the optical element.

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