A heterodyne interferometer for two-dimensional angular displacement measurement and a method of measurement

Abstract

The present application relates to the technical field of ultra-precision measurement, and particularly relates to a heterodyne interferometer for two-dimensional angular displacement measurement and a measurement method, wherein the heterodyne interferometer comprises a dual-frequency laser source for providing a dual-frequency laser beam with orthogonal polarizations, and is characterized in that a depolarization beam splitter prism is arranged on an output light path of the dual-frequency laser source, the dual-frequency laser beam is split into a first dual-frequency beam and a second dual-frequency beam after being incident on the depolarization beam splitter prism, and the two dual-frequency beams enter a plane interference measurement group and a vertical plane interference measurement group respectively; in the present application, the interference light path of each dimension is two axes, thereby avoiding the situation that measurement errors are caused by the decrease in parallelism due to the increase in the number of axes in the multi-axis measurement mode. Meanwhile, the two beams of light of each dimension are measurement light, thereby improving the resolution while suppressing common-mode noise and enhancing the anti-interference ability of the system.

Description

Technical Field

[0001] The present invention relates to the field of ultra-precision measurement technology, and in particular to a heterodyne interferometer and a measurement method for two-dimensional angular displacement measurement. Background Art

[0002] Lasers have many advantages, such as strong directionality, small beam angle, concentrated energy, high brightness, good monochromaticity and good coherence. Therefore, compared with microwave measurement equipment, ranging equipment using laser as a light source has obvious advantages in measurement directionality and accuracy, and is widely used in non-contact, high-precision measurement fields.

[0003] Since the invention of the first laser interferometer in 1967, it has been widely used in high-precision instrument calibration and verification, precision motion testing, and high-end equipment integration due to its wide range, high precision, traceability, and non-contact characteristics. Its operating principle is coherent detection, which is divided into two detection methods: heterodyne detection and homodyne detection. The essence of the heterodyne laser interferometer system is to use phase difference to demodulate displacement measurement information. The resulting photoelectric signal has a high signal-to-noise ratio, strong anti-interference ability, and is easy to achieve high-resolution measurement. It has attracted great attention and in-depth research in the fields of measurement research and industrial applications, and has achieved considerable development. Today, it is widely used in the field of geometric measurement and has long been popular.

[0004] At present, the mature products in the world mainly include the XL series single-frequency laser interferometers of Renishaw Company in the UK and the XD series of API Company in the United States. The heterodyne laser interferometer products mainly include the 5530 series of Keysight (formerly Agilent) Company in the United States and the ZMI series of ZYGO Company in the United States.

[0005] Domestically, many research institutions and universities have gradually begun researching laser interferometers, a development that spans two decades. Mature products include the S1500 from Harbin Ultra-Precision Engineering Technology Center Co., Ltd. (Harbin Ultra-Precision) and the MJS6A from Chengdu Tool Research Institute (CDI). Heterodyne laser interferometers include the HUE series from Harbin Ultra-Precision Engineering Technology Center Co., Ltd. and the MJS5 series from CDI. Furthermore, universities such as Tsinghua University and Harbin Institute of Technology have conducted targeted research on the core components and key performance indicators of homodyne and heterodyne interferometers, achieving breakthroughs in numerous areas.

[0006] After the heterodyne interferometer and the homodyne interferometer have been developed, in order to meet the measurement requirements in more fields, the multi-axis measurement interferometer is designed and developed to simultaneously detect the measured object in multiple directions. At present, the multi-axis measurement is generally achieved by using the traditional prism group to gradually split light, and the design and processing difficulty is extremely great, and the parallelism error in the light splitting process will be accumulated with the increase of the number of incident light beams. The enterprises such as Keysight and ZYGO realize high-precision parallel light splitting by using the prism group to gradually split light, and develop the multi-axis interferometer on this basis.

[0007] The parallelism between the optical axes of the three-axis interferometer group of the Keysight company is as high as 25 urad, but the parallelism of the optical axes of the five-axis interferometer group is reduced to 100 mrad. The reduction of parallelism greatly increases the linear error of measurement, and in addition, when the measurement distance is large, the turbulence in the air will also cause different degrees of disturbance to each axis measurement light beam, affecting the measurement stability of displacement and angle. SUMMARY

[0008] The purpose of the present application is to overcome the shortcomings of the existing heterodyne laser interferometric measurement method, and a two-dimensional angular displacement measurement heterodyne interferometer and a measurement method are provided. The device has the advantages of easy processing of components, more convenient light path adjustment, two axes in each dimension, which can avoid errors caused by reduced parallelism, two light paths in each axis, which can improve the anti-interference ability of the system, highly symmetrical design of the light path, which can avoid temperature drift, and finally realize high-precision two-dimensional angular displacement measurement.

[0009] In order to achieve the above purpose, the following technical solutions are adopted in the present application:

[0010] A two-dimensional angular displacement measurement heterodyne interferometer comprises a dual-frequency laser light source for providing a beam of orthogonally polarized dual-frequency laser light, a depolarization light splitting prism is arranged on the output light path of the dual-frequency laser light source, the dual-frequency laser light beam is split into a first dual-frequency light beam and a second dual-frequency light beam after being incident on the depolarization light splitting prism, and the two dual-frequency light beams enter a plane interference measurement group and a vertical plane interference measurement group respectively.

[0011] The plane interferometry measurement group includes a first half-wave plate, a first right-angle prism, and a first polarization beam splitter prism, the first half-wave plate is arranged on one side of the depolarization beam splitter prism, the first dual-frequency light beam passes through the first half-wave plate and the first right-angle prism in sequence and then enters the first polarization beam splitter prism, and is respectively formed into a first beam of measuring light and a second beam of measuring light after being transmitted and reflected by the first polarization beam splitter prism, a first target retroreflector is arranged on the outgoing optical path of the first beam of measuring light, a second right-angle prism and a second target retroreflector are arranged on the outgoing optical path of the second beam of measuring light, a first polarizer is attached to the rear end surface of the first polarization beam splitter prism, a first photodetector is arranged on the outgoing optical path of the first polarizer, a second half-wave plate is arranged on one side of the first polarization beam splitter prism, and a laser length measuring instrument is arranged after the second half-wave plate;

[0012] The vertical interferometry measurement group includes a third half-wave plate and a second polarization beam splitter prism, the third half-wave plate is arranged on one side of the depolarization beam splitter prism, the second dual-frequency light beam enters the second polarization beam splitter prism after passing through the third half-wave plate, and forms a third beam of measuring light and a fourth beam of measuring light after being transmitted and reflected by the second polarization beam splitter prism, respectively, a third right-angle prism and a third target retroreflector are arranged in sequence on the outgoing optical path of the fourth beam of measuring light, a fourth right-angle prism, a fifth right-angle prism, and a fourth target retroreflector are arranged in sequence on the outgoing optical path of the third beam of measuring light, a second polarizer is attached to the rear end face of the second polarization beam splitter prism, and a second photodetector is arranged on the outgoing optical path of the second polarizer;

[0013] The first target retroreflective mirror, the second target retroreflective mirror, the third target retroreflective mirror and the fourth target retroreflective mirror are all arranged on a rotating table, and horizontal rotating shafts are arranged on both sides of the rotating table, and the horizontal rotating shaft is rotatably connected to the intermediate turntable. Vertical rotating shafts are arranged on the upper and lower sides of the intermediate turntable, and the vertical rotating shaft is rotatably connected to the fixed table. The vertical rotating shaft provides vertical rotation power for the intermediate turntable through an external servo motor, and the horizontal rotating shaft provides horizontal rotation power for the rotating table through an external servo motor. The first target retroreflective mirror and the second target retroreflective mirror are distributed at positions close to the vertical rotating shaft, and the third target retroreflective mirror and the fourth target retroreflective mirror are distributed at positions close to the horizontal rotating shaft. Through the cooperation of the vertical rotating shaft and the horizontal rotating shaft, the angle adjustment of the first target retroreflective mirror, the second target retroreflective mirror, the third target retroreflective mirror and the fourth target retroreflective mirror in three-dimensional space is realized.

[0014] Furthermore, the polarization axes of the first polarizer and the second polarizer are both at an angle of 45° to the horizontal direction.

[0015] Furthermore, the first half-wave plate, the second half-wave plate and the third half-wave plate are all installed in a rotationally connected manner.

[0016] A two-dimensional angular displacement measurement method comprises the following steps:

[0017] S1, after the dual-frequency laser beam is incident on the depolarization beam splitter prism, the transmitted beam forms the second dual-frequency beam, and the reflected beam forms the first dual-frequency beam;

[0018] S2: The first dual-frequency light beam passes through the first half-wave plate and the first right-angle prism in sequence and is incident on the first polarization beam splitter prism. The transmitted light beam forms the first measurement beam, and the reflected light beam forms the second measurement beam. The second dual-frequency light beam passes through the third half-wave plate and is incident on the second polarization beam splitter prism. The transmitted light beam forms the third measurement beam, and the reflected light beam forms the fourth measurement beam.

[0019] S3, the first beam of measuring light contacts the first target retroreflector mirror, carries the Doppler frequency shift, and is transmitted through the first polarization splitting prism and output; the second beam of measuring light is reflected by the second right-angle prism and contacts the second target retroreflector mirror, then reflects by the second right-angle prism and reflects through the first polarization splitting prism and output; the third beam of measuring light contacts the third target retroreflector mirror after being reflected by the fourth right-angle prism and the fifth right-angle prism, then reflects by the fifth right-angle prism and the fourth right-angle prism, then transmits through the second polarization splitting prism and output; the fourth beam of measuring light contacts the third target retroreflector mirror after being reflected by the third right-angle prism, then reflects by the third right-angle prism and reflects through the second polarization splitting prism and output;

[0020] S4: After passing through the first polarization beam splitter prism, the paths of the first and second measuring beams overlap, and then pass through the first polarizer for beat frequency interference to form a first measurement signal Im1. After passing through the second polarization beam splitter prism, the paths of the third and fourth measuring beams overlap, and then pass through the second polarizer for beat frequency interference to form a second measurement signal Im2.

[0021] S5, the first photodetector receives a first measurement signal Im1, and the second photodetector receives a second measurement signal Im2. After signal processing of the first measurement signal Im1 and the second measurement signal Im2, the angular displacement of the object to be measured on two axes can be obtained.

[0022] Furthermore, the dual-frequency laser beam is generated by a dual-acousto-optic modulation method.

[0023] Furthermore, the interference light path in each dimension consists of two axes, avoiding the measurement error caused by the decrease in parallelism as the number of axes increases in multi-axis measurement methods; at the same time, the two beams of light in each dimension are measurement light, which improves the resolution while suppressing common-mode noise and enhancing the system's anti-interference ability.

[0024] Furthermore, the angular displacement of the object to be measured on two axes can be calibrated to its initial position and final position in three-dimensional space in a spherical coordinate system, thereby achieving high-precision measurement of two-dimensional angular displacement.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The present invention only includes two-dimensional interference light paths. On the one hand, the volume is smaller than the current multi-axis interferometer. On the other hand, the component processing is more convenient and the optical path adjustment is simpler.

[0027] 2. The present invention uses two interferometric optical paths in each dimension, avoiding the measurement errors caused by the loss of parallelism as the number of axes increases in multi-axis measurement. Furthermore, both beams in each dimension serve as measurement light, improving resolution while suppressing common-mode noise and enhancing the system's anti-interference capabilities.

[0028] 3. The vertical interferometry measurement group in the present invention is highly symmetrically designed, which avoids the idle path error caused by the different initial optical path lengths of the two arms. For the plane interferometry measurement group, a laser length measuring instrument is introduced to measure the optical path lengths of the two arms, and the initial optical path difference is calculated, which can be compensated in data processing to eliminate the idle path error. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention;

[0030] Figure 2 This is the optical path diagram of the plane interferometry measurement group in the present invention;

[0031] Figure 3 This is the optical path diagram of the neutral plane interferometry measurement group of the present invention;

[0032] Figure 4 Schematic diagram of the installation structure of the rotating table in the present invention;

[0033] Figure 5 This is a diagram showing the measurement results of the horizontal dimension zero point of the present invention;

[0034] Figure 6 This is a diagram showing the measurement results of the vertical dimension zero point of the present invention;

[0035] Figure 7 This is a diagram showing the verification measurement results of the horizontal dimension angular displacement of the present invention;

[0036] Figure 8 This is a diagram showing the verification measurement results of the vertical dimension angular displacement of the present invention;

[0037] Figure 9 It is a two-dimensional angular displacement geometric space representation diagram of the present invention;

[0038] In the figure: dual-frequency laser light source 1, depolarizing beam splitter prism 2, plane interferometry group 3, vertical interferometry group 4, rotating stage 5, vertical rotation axis 6, horizontal rotation axis 7, intermediate rotating stage 8, fixed stage 9, first half-wave plate 301, first right-angle prism 302, first polarizing beam splitter prism 303, first target retroreflective mirror 304, second right-angle prism 305, second target retroreflective mirror 306, first polarizer 307, first photodetector 308, second half-wave plate 309, laser length measuring instrument 310, third half-wave plate 401, second polarizing beam splitter prism 402, third right-angle prism 403, third target retroreflective mirror 404, fourth right-angle prism 405, fifth right-angle prism 406, fourth target retroreflective mirror 407, second polarizer 408, second photodetector 409. DETAILED DESCRIPTION

[0039] In order to further illustrate the technical solution of the present invention, the present invention is further described below through examples.

[0040] like Figures 1 to 4 As shown, a heterodyne interferometer for two-dimensional angular displacement measurement includes a dual-frequency laser light source 1 for providing a dual-frequency laser beam with orthogonal polarizations. A depolarizing beam splitter prism 2 is provided on the output optical path of the dual-frequency laser light source 1. After the dual-frequency laser beam is incident on the depolarizing beam splitter prism 2, it is split into a first dual-frequency beam and a second dual-frequency beam. The two dual-frequency beams enter a plane interferometry group 3 and a vertical interferometry group 4, respectively.

[0041] The plane interferometry measurement group 3 includes a first half-wave plate 301, a first right-angle prism 302 and a first polarization beam splitter prism 303. The first half-wave plate 301 is arranged on one side of the depolarization beam splitter prism 2. The first dual-frequency light beam passes through the first half-wave plate 301 and the first right-angle prism 302 in sequence and then enters the first polarization beam splitter prism 303. After being transmitted and reflected by the first polarization beam splitter prism 303, the first measurement light beam and the second measurement light beam are formed respectively. The outgoing optical path of the first measurement light beam is A first target retroreflector 304 is provided on the upper surface, a second right-angle prism 305 and a second target retroreflector 306 are provided on the outgoing optical path of the second measuring light beam, a first polarizer 307 is attached to the rear end surface of the first polarizer 307, a first photodetector 308 is provided on the outgoing optical path of the first polarizer 307, a second half-wave plate 309 is provided on one side of the first polarizer 303, and a laser length measuring instrument 310 is provided behind the second half-wave plate 309;

[0042] The facade interferometry group 4 comprises a third half-wave plate 401 and a second polarization beam splitter prism 402, the third half-wave plate 401 is arranged on one side of the depolarization beam splitter prism 2, the second dual-frequency light beam passes through the third half-wave plate 401 and then enters the second polarization beam splitter prism 402, and after transmission and reflection of the second polarization beam splitter prism 402, a third measurement light beam and a fourth measurement light beam are formed, respectively, a third right-angle prism 403 and a third target retroreflector 404 are arranged in sequence on the exit light path of the fourth measurement light beam, a fourth right-angle prism 405, a fifth right-angle prism 406 and a fourth target retroreflector 407 are arranged in sequence on the exit light path of the third measurement light beam, a second polaroid 408 is attached to the rear end face of the second polarization beam splitter prism 402, and a second photodetector 409 is arranged on the exit light path of the second polaroid 408.

[0043] The polarization axis directions of the first polaroid 307 and the second polaroid 408 are both 45° with the horizontal direction. The first half-wave plate 301, the second half-wave plate 309 and the third half-wave plate 401 are all installed in a rotating connection mode.

[0044] The first target retroreflector 304, the second target retroreflector 306, the third target retroreflector 404 and the fourth target retroreflector 407 are all arranged on the rotating table 5, horizontal rotation shafts 7 are arranged on both sides of the rotating table 5, the horizontal rotation shafts 7 are rotationally connected with an intermediate rotating table 8, vertical rotation shafts 6 are arranged on the upper and lower sides of the intermediate rotating table 8, the vertical rotation shafts 6 are rotationally connected with a fixed table 9, the vertical rotation shafts 6 provide vertical rotation power for the intermediate rotating table 8 through an external servo motor, the horizontal rotation shafts 7 provide horizontal rotation power for the rotating table 5 through an external servo motor, the first target retroreflector 304 and the second target retroreflector 306 are distributed close to the vertical rotation shaft 6, the third target retroreflector 404 and the fourth target retroreflector 407 are distributed close to the horizontal rotation shaft 7, and through cooperation of the vertical rotation shaft 6 and the horizontal rotation shaft 7, angle adjustment of the first target retroreflector 304, the second target retroreflector 306, the third target retroreflector 404 and the fourth target retroreflector 407 in a three-dimensional space is realized.

[0045] A two-dimensional angle displacement measurement method, comprising the following steps:

[0046] S1, after a dual-frequency laser beam is incident to the depolarization beam splitter prism 2, a transmitted beam forms a second dual-frequency light beam, and a reflected beam forms a first dual-frequency light beam, the dual-frequency laser beam is generated by a dual-acoustic-optic modulation method;

[0047] S2, the first dual-frequency light beam sequentially passes through the first half-wave plate 301, the first right-angle prism 302, and then is incident to the first polarization beam splitter prism 303, the transmitted light beam of which forms the first measurement light, and the reflected light beam forms the second measurement light; the second dual-frequency light beam passes through the third half-wave plate 401 and is incident to the second polarization beam splitter prism 402, the transmitted light beam of which forms the third measurement light, and the reflected light beam forms the fourth measurement light;

[0048] S3, the first measurement light carries the Doppler frequency shift after contacting the first target retroreflector 304 and is transmitted out of the first polarization beam splitter prism 303, the second measurement light is reflected by the second right-angle prism 305, contacts the second target retroreflector 306, and then carries the Doppler frequency shift and is reflected by the second right-angle prism 305 and is reflected out of the first polarization beam splitter prism 303; the third measurement light contacts the third target retroreflector 404 after being reflected by the fourth right-angle prism 405 and the fifth right-angle prism 406, then carries the Doppler frequency shift and is reflected by the fifth right-angle prism 406 and the fourth right-angle prism 405 and is transmitted out of the second polarization beam splitter prism 402, and the fourth measurement light contacts the third target retroreflector 404 after being reflected by the third right-angle prism 403, then carries the Doppler frequency shift and is reflected by the third right-angle prism 403 and is reflected out of the second polarization beam splitter prism 402;

[0049] S4, the first measurement light and the second measurement light have the same path after passing through the first polarization beam splitter prism 303, then pass through the first polarizer 307 and form the first measurement signal Im1 through beat interference; the third measurement light and the fourth measurement light have the same path after passing through the second polarization beam splitter prism 402, then pass through the second polarizer 408 and form the second measurement signal Im2 through beat interference;

[0050] S5, the first photoelectric detector 308 receives the first measurement signal Im1, the second photoelectric detector 409 receives the second measurement signal Im2, and the angular displacement of the measured object on the two axes can be obtained after the first measurement signal Im1 and the second measurement signal Im2 are processed.

[0051] The interference light path of each dimension is two axes, which avoids the case that the parallelism is reduced and the measurement error is caused with the increase of the number of axes in the multi-axis measurement mode; meanwhile, the two light beams of each dimension are measurement light, which improves the resolution while suppressing common-mode noise and enhances the anti-interference ability of the system. The angular displacement of the measured object on the two axes can be used to calibrate the initial position and the final position of the measured object in the three-dimensional space under the spherical coordinate system, so as to realize high-precision measurement of two-dimensional angular displacement.

[0052] As shown in Figure 5 , Figure 6 It can be known from the figure that the standard deviation of the original angular displacement information obtained by the application is about 3 mas, which can represent the stability of the whole system;

[0053] Figure 7 The figure is the verification measurement result of the horizontal dimension angular displacement of the application; the angular displacement range of the turntable is 0-3.5°, the red part is the standard deviation of the selected data at the static moment, the unit is second; Figure 8 The figure is the verification measurement result of the vertical dimension angular displacement of the application; the angular displacement range of the turntable is 0-3.5°, the standard deviation of each static moment is one order of magnitude different from the horizontal direction measurement result, because the vertical direction system stability is poor. Figure 7 、 Figure 8 It can be seen that the application can realize the measurement of two-dimensional angular displacement.

[0054] As shown in Figure 9 , the initial and ending states of the measured object in the application when producing angular displacement, using the normal line of the measured object to represent its direction, the angular displacement state of the measured object can be described under the spherical coordinate system, assuming that the initial measured object position is located in the XOZ plane, then its normal line can be represented as (1, π, π), the measured object produces φ angular displacement around the Z axis, and produces θ angular displacement around the X axis, then the final position can be represented as (1, π+θ, π+φ) under the spherical coordinate system. Through this representation method, the initial position and final position of the measured object in the three-dimensional space can be calibrated, and the accurate description of two-dimensional angular displacement can be realized.

[0055] Figure 9 The figure is the geometric space representation of two-dimensional angular displacement of the application; the main features and advantages of the application are shown and described above, for those skilled in the art, it is obvious that the specific embodiments of the application are not limited to the details of the above exemplary embodiments, and the inventive idea and design idea of the application can be realized in other specific forms without departing from the spirit or basic characteristics of the application, which should be equivalent to the protection scope disclosed in the technical scheme of the application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the application is defined by the appended claims rather than the above description, therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the application.

[0056] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, the description manner of the specification is only for the sake of clarity, those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be properly combined to form other embodiments that those skilled in the art can understand.

Claims

1. A heterodyne interferometer for two-dimensional angular displacement measurement, comprising a dual-frequency laser light source (1) for providing a dual-frequency laser beam with orthogonal polarizations, characterized in that: A depolarizing beam splitter prism (2) is provided on the output optical path of the dual-frequency laser light source (1); the dual-frequency laser beam is incident on the depolarizing beam splitter prism (2) and is split into a first dual-frequency beam and a second dual-frequency beam; the two dual-frequency beams enter the plane interferometry group (3) and the elevation interferometry group (4), respectively; The plane interference measurement group (3) comprises a first half-wave plate (301), a first right-angle prism (302) and a first polarization beam splitter prism (303). The first half-wave plate (301) is arranged on one side of the depolarization beam splitter prism (2). The first dual-frequency light beam passes through the first half-wave plate (301) and the first right-angle prism (302) in sequence and then enters the first polarization beam splitter prism (303). After being transmitted and reflected by the first polarization beam splitter prism (303), the first beam of measurement light and the second beam of measurement light are respectively formed. On the outgoing optical path of the first beam of measurement light, the first dual-frequency light beam passes through the first half-wave plate (301) and the first right-angle prism (302). A first target retroreflector (304) is provided, a second right-angle prism (305) and a second target retroreflector (306) are provided on the outgoing light path of the second beam of measuring light, a first polarizing plate (307) is attached to the rear end surface of the first polarizing beam splitter prism (303), a first photodetector (308) is provided on the outgoing light path of the first polarizing plate (307), a second half-wave plate (309) is provided on one side of the first polarizing beam splitter prism (303), and a laser length measuring instrument (310) is provided behind the second half-wave plate (309); The vertical interferometry measurement group (4) includes a third half-wave plate (401) and a second polarization beam splitter prism (402), the third half-wave plate (401) is arranged on one side of the depolarization beam splitter prism (2), the second dual-frequency light beam passes through the third half-wave plate (401) and enters the second polarization beam splitter prism (402), and forms a third beam of measurement light and a fourth beam of measurement light respectively after being transmitted and reflected by the second polarization beam splitter prism (402), a third right-angle prism (403) and a third target retroreflector (404) are sequentially arranged on the outgoing light path of the fourth beam of measurement light, a fourth right-angle prism (405), a fifth right-angle prism (406), and a fourth target retroreflector (407) are sequentially arranged on the outgoing light path of the third beam of measurement light, a second polarizer (408) is attached to the rear end face of the second polarization beam splitter prism (402), and a second photodetector (409) is arranged on the outgoing light path of the second polarizer (408); The first target retroreflective mirror (304), the second target retroreflective mirror (306), the third target retroreflective mirror (404) and the fourth target retroreflective mirror (407) are all arranged on a rotating platform (5). Horizontal rotating shafts (7) are arranged on both sides of the rotating platform (5). The horizontal rotating shafts (7) are rotatably connected to the intermediate rotating platform (8). Vertical rotating shafts (6) are arranged on the upper and lower sides of the intermediate rotating platform (8). The vertical rotating shafts (6) are rotatably connected to the fixed platform (9). The vertical rotating shafts (6) provide vertical rotation power to the intermediate rotating platform (8) through an external servo motor. The horizontal rotating shafts (7) are rotatably connected to the fixed platform (9). ) provides horizontal rotation power for the rotating table (5) through an external servo motor, the first target retroreflective mirror (304) and the second target retroreflective mirror (306) are distributed at positions close to the vertical rotation axis (6), and the third target retroreflective mirror (404) and the fourth target retroreflective mirror (407) are distributed at positions close to the horizontal rotation axis (7). Through the cooperation of the vertical rotation axis (6) and the horizontal rotation axis (7), the angle adjustment of the first target retroreflective mirror (304), the second target retroreflective mirror (306), the third target retroreflective mirror (404) and the fourth target retroreflective mirror (407) in three-dimensional space is achieved.

2. The heterodyne interferometer for two-dimensional angular displacement measurement according to claim 1, characterized in that: The polarization axis directions of the first polarizer (307) and the second polarizer (408) are both 45 degrees to the horizontal direction.

3. The heterodyne interferometer for two-dimensional angular displacement measurement according to claim 1, characterized in that: The first half-wave plate (301), the second half-wave plate (309), and the third half-wave plate (401) are all installed in a rotationally connected manner.

4. A two-dimensional angular displacement measurement method using the heterodyne interferometer according to claim 1, characterized in that: The following steps are involved: S1, after the dual-frequency laser beam is incident on the depolarization beam splitter prism (2), the transmitted beam forms a second dual-frequency beam, and the reflected beam forms a first dual-frequency beam; S2, the first dual-frequency light beam passes through the first half-wave plate (301) and the first right-angle prism (302) in sequence and is incident on the first polarization beam splitter prism (303), wherein the transmitted light beam forms the first beam of measurement light, and the reflected light beam forms the second beam of measurement light; the second dual-frequency light beam passes through the third half-wave plate (401) and is incident on the second polarization beam splitter prism (402), wherein the transmitted light beam forms the third beam of measurement light, and the reflected light beam forms the fourth beam of measurement light; S3, the first beam of measuring light contacts the first target retroreflector (304) with a Doppler frequency shift and is transmitted and outputted from the first polarization splitting prism (303); the second beam of measuring light is reflected by the second right-angle prism (305) and contacts the second target retroreflector (306); thereafter, it is reflected by the second right-angle prism (305) with a Doppler frequency shift and is reflected and outputted from the first polarization splitting prism (303); the third beam of measuring light is reflected by the fourth right-angle prism (405) and the fifth right-angle prism (406) and contacts the third target retroreflector (404); thereafter, it is reflected by the fifth right-angle prism (406) and the fourth right-angle prism (405) with a Doppler frequency shift and is transmitted and outputted from the second polarization splitting prism (402); the fourth beam of measuring light is reflected by the third right-angle prism (403) and contacts the third target retroreflector (404); thereafter, it is reflected by the third right-angle prism (403) with a Doppler frequency shift and is reflected and outputted from the second polarization splitting prism (402); S4, the paths of the first beam of measuring light and the second beam of measuring light coincide after passing through the first polarization beam splitter prism (303), and then pass through the first polarizer (307) to generate beat frequency interference to form a first measurement signal Im1; the paths of the third beam of measuring light and the fourth beam of measuring light coincide after passing through the second polarization beam splitter prism (402), and then pass through the second polarizer (408) to generate beat frequency interference to form a second measurement signal Im2; S5, the first photodetector (308) receives a first measurement signal Im1, and the second photodetector (409) receives a second measurement signal Im2. After signal processing, the first measurement signal Im1 and the second measurement signal Im2 can be used to obtain the angular displacement of the object being measured on two axes.

5. A two-dimensional angular displacement measurement method according to claim 4, characterized in that: The dual-frequency laser beam is generated by a dual-acousto-optic modulation method.

6. A two-dimensional angular displacement measurement method according to claim 4, characterized in that: The interference optical path in each dimension consists of two axes, avoiding the measurement errors caused by the decrease in parallelism as the number of axes increases in multi-axis measurement methods. At the same time, both beams of light in each dimension are measurement light, which improves resolution while suppressing common-mode noise and enhances the system's anti-interference ability.

7. A two-dimensional angular displacement measurement method according to claim 4, characterized in that: The angular displacement of the measured object on two axes can be used to calibrate its initial position and final position in three-dimensional space in a spherical coordinate system, thereby achieving high-precision measurement of two-dimensional angular displacement.

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