Device and method for testing pm-level displacement resolution of laser interferometer

Abstract

The invention discloses a device and a method for testing pm-level displacement resolution of a laser interferometer, and belongs to the technical field of optical measurement. The problem that the pm-level displacement resolution of a laser interferometer cannot be measured and cannot be accurately measured is solved. The device comprises a fixed reflecting mirror, an optical glass plate, a connecting shaft, a motion generating device and a standard device, the fixed reflector is used for reflecting the laser transmitted through the optical glass plate in the measuring light path, so that the reflected laser returns to the laser interferometer along the same path; the optical glass plate is installed on a connecting shaft of the motion generating device and located on a measuring light path between the laser interferometer and the fixed reflecting mirror, the geometric center of the optical glass plate is located on an extension line of the connecting shaft of the motion generating device, and one face of the optical glass plate is perpendicular to the connecting shaft. By controlling the movement of the optical glass plate, the equivalent phase shift generated by the displacement from the nm level to the pm level in the laser interferometer is realized, the pm level displacement resolution test of the laser interferometer is more sufficient, and the test precision is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to a laser interferometer pm-level displacement resolution testing device and a method thereof. Background Art

[0002] Laser interferometry displacement measurement technology is widely used in ultra-precision machining, microelectronics manufacturing, precision equipment installation and calibration, and large scientific facilities due to its advantages of high resolution, non-contact, strong anti-interference ability, and traceability, becoming one of the important technologies in the field of ultra-precision displacement measurement. The minimum displacement that an interferometer can measure, that is, the resolution of the interferometer, is one of the important indicators for evaluating the performance of the interferometer, and directly determines whether it can be used in ultra-high precision measurement and metrology scenarios. Therefore, a complete, reliable, and accurate resolution test of the laser interferometer is of great significance to the evaluation of the interferometer performance.

[0003] With the advancement of technology, various application scenarios such as ultra-precision machining, microelectronics manufacturing, and precision equipment installation have put forward nm-level, sub-nm-level, and even pm-level measurement resolution requirements for laser interferometers. Direct evaluation is performed using a displacement generator standard. The only generator standard can only evaluate laser interferometers with a lower resolution accuracy than itself. For example, PI's P-753 piezoelectric displacement stage has a resolution of 0.1nm and can only evaluate laser interferometers with a displacement resolution accuracy lower than 0.1nm. In addition, the evaluation process requires high installation accuracy of the laser interferometer. However, there is currently a lack of standard tools that can accurately generate pm-level displacements for laser interferometer measurement resolution testing.

[0004] Pengcheng Hu from Harbin Institute of Technology proposed a scheme based on changing the beat frequency phase by spatial movement (D.Chang, J.Wang, P.Hu et al. “Zoom into picometer: a picoscale equivalent phase-difference-generating method for testing heterodyne interferometers without ultraprecision stages[J].” Optical Engineering 58(2019):064101-064101). Without generating Doppler frequency shift, the sub-nanometer displacement is converted into the interference signal phase, and then converted into mm-level spatial displacement for testing. This scheme can test the light source and signal processing links, avoiding the influence of environmental fluctuations, Abbe errors, vibrations and other factors. However, the interference mirror group is missing in the measurement process, and it does not constitute an interference optical path, so the test of the overall resolution of the interferometer is insufficient.

[0005] Perform a complete uncertainty analysis on the laser interferometer or compare it with laser interferometers of the same accuracy level. For example, (S. Rene. "Accurate extraction of thermal expansion coefficients and their uncertainties from high precision interferometric length measurements [C]." SPIE Optics Photonics (2005)) evaluates the uncertainty of each measurement process and then evaluates the measurement accuracy and resolution of the laser interferometer. However, this method is difficult to determine all uncertainties. Although it can accurately evaluate the resolution of the interferometer with a certain accuracy, it still has some shortcomings. Summary of the invention

[0006] The problem to be solved by the present invention is to improve the measurement accuracy of the pm level displacement resolution of a laser interferometer, and a device and method for testing the pm level displacement resolution of a laser interferometer are proposed.

[0007] To achieve the above object, the present invention is implemented through the following technical solutions:

[0008] A laser interferometer pm level displacement resolution test device, comprising a fixed reflector, an optical glass plate, a connecting shaft, a motion generating device, and a standard device;

[0009] The fixed reflector is used to reflect the laser light transmitted through the optical glass plate in the measuring light path, so that the reflected laser light returns to the laser interferometer along the original path;

[0010] The optical glass plate is mounted on the connecting shaft of the motion generating device, the optical glass plate is located on the measuring optical path between the laser interferometer and the fixed reflector, the geometric center of the optical glass plate is located on the extension line of the connecting shaft of the motion generating device, and one side of the optical glass plate is perpendicular to the connecting shaft;

[0011] The motion generating device is used to control the connecting shaft to drive the optical glass plate to rotate a specified angle or move a specified displacement;

[0012] The standard device is placed opposite to the motion generating device, and the standard device is used to measure the true value of the angle or displacement generated by the motion generating device;

[0013] The laser emitted by the laser interferometer passes through the optical glass plate, then is incident on the fixed reflector and reflected back to the laser interferometer along the original path. The reflected laser interferes with the reference light inside the laser interferometer.

[0014] Set the direction of the measuring optical path to the Y axis, the X axis and the Y axis form a horizontal plane, and the Z axis is perpendicular to the horizontal plane;

[0015] The initial position of the optical glass plate is that the emitted laser of the laser interferometer is perpendicular to the incident surface of the optical glass plate, or the point where the emitted laser of the laser interferometer is perpendicular to the incident surface of the optical glass plate is rotated clockwise or counterclockwise around the Z axis or the X axis by an initial angle γ.

[0016] Furthermore, the range of the initial angle γ is 0°≤γ<90°, and 0° is the position when the laser is vertically incident on the optical glass plate.

[0017] Furthermore, the motion generating device drives the optical glass plate to rotate clockwise or counterclockwise around the Z axis or the X axis from the initial position by a specified angle β or to move a certain displacement along the X axis from the initial position.

[0018] Furthermore, the value of the specified angle β or displacement is calculated by substituting the value of the resolution of the laser interferometer to be tested into the formula of the geometric optical path change ΔL generated by the optical glass plate.

[0019] A method for testing a pm-level displacement resolution of a laser interferometer is implemented based on the pm-level displacement resolution testing device of a laser interferometer, and comprises the following steps:

[0020] Insert an optical glass plate into the measuring optical path, set the initial position of the optical glass plate to be the point where the laser interferometer emits laser light perpendicular to the incident surface of the optical glass plate, or rotate the point where the laser interferometer emits laser light perpendicular to the incident surface of the optical glass plate clockwise or counterclockwise around the Z axis or X axis by an initial angle γ;

[0021] Start the laser interferometer light source, and the laser interferometer emits laser to the measuring optical path;

[0022] The laser beam in the measuring optical path is transmitted through the optical glass plate, hits the fixed reflector and returns to the interferometer along the original path after being reflected, and interferes with the reference light inside the interferometer.

[0023] Control the motion generating device to drive the optical glass plate to rotate a specified angle or move a specified displacement and monitor whether the rotation angle or motion displacement of the motion generating device is correct through a standard device, and the value of the specified angle β or displacement is based on the value detected by the standard device;

[0024] Observe the displacement change information output by the laser interferometer, and compare it with the geometric optical path change ΔL caused by rotating or moving the optical glass plate. If the displacement change information output by the laser interferometer and ΔL are the same step signal, it indicates that the displacement resolution of the laser interferometer reaches ΔL.

[0025] Furthermore, when the optical glass plate is a parallel optical glass plate, assuming that the thickness of the parallel optical glass plate is d, the length is r, the parallelism is α, and the initial position of the parallel optical glass plate is such that the laser is vertically incident on the parallel optical glass plate, the expression for measuring the optical path L of the laser is:

[0026] L=2n1L1+2n2d

[0027] Where n1 is the refractive index of the measuring environment, n2 is the refractive index of the parallel optical glass plate, and L1 is the geometric length of the optical path of the laser except the optical path in the parallel optical glass plate;

[0028] When the parallel optical glass plate is rotated by a specified angle β, the expression of the optical path L′ of the laser light after the rotation is:

[0029] L′=2n1(L1-δ)+2n2(d+δ)

[0030] Wherein, δ is the optical path length of the laser beam in the parallel optical glass plate increased by the rotation of the parallel optical glass plate;

[0031] Therefore, the expression of the optical path ΔL' increased by the rotating parallel optical glass plate in the measuring optical path laser is:

[0032] ΔL'=2(n2-n1)δ

[0033] The expression of δ is:

[0034]

[0035] Where x0 is the distance from the center of the laser beam to one side of the parallel optical glass plate, 0<x0<r;

[0036] Substituting the formula of δ into the optical path increase of the laser in the measuring optical path caused by rotating the parallel optical glass plate, we get:

[0037]

[0038] Then the geometric optical path change ΔL caused by rotating the parallel optical glass plate is:

[0039]

[0040] Furthermore, when the initial position of the parallel optical glass plate is a point where the emitted laser of the laser interferometer is perpendicular to the incident surface of the optical glass plate and rotates clockwise or counterclockwise around the Z axis or X axis at an initial angle γ, the expression for measuring the optical path laser L is:

[0041] L=2n1L1+2n2d

[0042] Where n1 is the refractive index of the measuring environment, n2 is the refractive index of the parallel optical glass plate, and L1 is the geometric length of the optical path of the laser except the optical path in the parallel optical glass plate;

[0043] When the parallel optical glass plate is rotated by a specified angle β, the expression of the optical path L′ of the laser light after the rotation is:

[0044] L′=2n1(L1-δ)+2n2(d+δ)

[0045] Where δ is the optical path length of the laser beam in the parallel optical glass plate increased by the rotation of the glass plate;

[0046] Therefore, the expression of the optical path ΔL' increased by the rotating parallel optical glass plate in the measuring optical path laser is:

[0047] ΔL'=2(n2-n1)δ

[0048] The expression of δ is:

[0049]

[0050] Substituting the formula of δ into the optical path increase of the laser in the measuring optical path caused by rotating the parallel optical glass plate, we get:

[0051]

[0052] Then the geometric optical path change ΔL caused by rotating the parallel optical glass plate is:

[0053]

[0054] Furthermore, when the optical glass plate is a wedge-shaped optical glass plate, θ is the wedge angle of the wedge-shaped optical glass plate, and the initial position of the wedge-shaped optical glass plate is such that the laser is vertically incident on the surface of the wedge-shaped optical glass plate that is perpendicular to the Y axis, the geometric optical path change ΔL″ generated by moving the wedge-shaped optical glass plate is:

[0055]

[0056] Where n1 is the refractive index of the measurement environment and n'2 is the refractive index of the wedge-shaped optical glass plate.

[0057] Beneficial effects of the present invention:

[0058] The pm level displacement resolution test device of the laser interferometer described in the present invention can test all laser interferometer mechanisms including the interferometer lens group, so that the pm level displacement resolution of the laser interferometer can be more effectively evaluated. The motion generating device changes the optical path of the light beam on the measuring arm, and the phase shift introduced by the angle change from arc seconds to hundreds of arc seconds is equivalent to the phase shift introduced by the nm to pm level displacement in the laser interferometer, thereby enhancing the anti-interference ability of the test device and improving the test accuracy of the resolution.

[0059] The laser interferometer pm level displacement resolution test device described in the present invention uses a fixed reflector to reflect the outgoing light, and utilizes a motion generating device in combination with an optical glass plate to change the laser optical path, thereby avoiding the interference of Abbe error on the resolution test during the movement of the guide rail; the test device has the characteristics of simple structure and simple operation, and can be directly used for the laser interferometer pm level displacement resolution test without additional adjustment, and is more suitable for the application of the laser interferometer pm level displacement resolution test. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a structural schematic diagram of a laser interferometer pm-level displacement resolution testing device according to the present invention;

[0061] Figure 2 Schematic diagram of the size and light beam position of the parallel optical glass plate described in Examples 2, 3, 4, and 5 of the present invention;

[0062] Figure 3 It is a schematic diagram of an implementation method of a laser interferometer pm-level displacement resolution testing device according to Example 2 of the present invention;

[0063] Figure 4 It is a schematic diagram of an implementation method of a laser interferometer pm level displacement resolution testing device as described in Example 3 of the present invention;

[0064] Figure 5 It is a schematic diagram of an implementation method of a laser interferometer pm-level displacement resolution testing device according to Example 4 of the present invention;

[0065] Figure 6 It is a schematic diagram of an implementation method of a laser interferometer pm-level displacement resolution testing device according to Example 5 of the present invention;

[0066] Figure 7 Graph showing the effect of the change in the center position of the light beam on the change in the optical path achieved by rotation in Example 2;

[0067] Figure 8 This is a simulation result diagram of a test method of a laser interferometer pm-level displacement resolution test device described in Example 2;

[0068] Fig. 9 A top view of a schematic diagram of an implementation method of a laser interferometer pm-level displacement resolution testing device according to Example 6 of the present invention;

[0069] Fig.10 This is a front view of a schematic diagram of an implementation method of a laser interferometer pm-level displacement resolution testing device as described in Example 6 of the present invention.

[0070] Fig.11 Schematic diagram of the size and light beam position of the wedge-shaped optical glass plate described in Example 6 of the present invention. DETAILED DESCRIPTION

[0071] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0072] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected specific embodiments of the present invention. Based on the specific embodiments of the present invention, all other specific embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0073] In order to further understand the content, features and effects of the present invention, the following specific implementation methods are given as examples, and the attached Figure 1 -Attached Fig.11 The detailed instructions are as follows:

[0074] Embodiment 1:

[0075] A laser interferometer pm level displacement resolution test device comprises a fixed reflector 1, an optical glass plate 2, a connecting shaft 3, a motion generating device 4, and a standard device 6;

[0076] The fixed reflector 1 is used to reflect the laser light transmitted through the optical glass plate 2 in the measuring light path, so that the reflected laser light returns to the laser interferometer 5 along the original path;

[0077] The optical glass plate 2 is mounted on the connecting shaft 3 of the motion generating device 4, the optical glass plate 2 is located on the measuring optical path between the laser interferometer 5 and the fixed reflector 1, the geometric center of the optical glass plate 2 is located on the extension line of the connecting shaft 3 of the motion generating device 4, and one side of the optical glass plate 2 is perpendicular to the connecting shaft 3;

[0078] The motion generating device 4 is used to control the connecting shaft 3 to drive the optical glass plate 2 to rotate a specified angle or move a specified displacement;

[0079] The standard device 6 is placed opposite to the motion generating device 4, and the standard device 6 is used to measure the true value of the angle or displacement generated by the motion generating device 4;

[0080] The emitted laser of the laser interferometer 5 is transmitted through the optical glass plate 2, then incident on the fixed reflector 1 and reflected back to the laser interferometer 5 along the original path, and the reflected laser interferes with the reference light inside the laser interferometer 5;

[0081] Set the direction of the measuring optical path to the Y axis, the X axis and the Y axis form a horizontal plane, and the Z axis is perpendicular to the horizontal plane;

[0082] The initial position of the optical glass plate 2 is that the laser emitted by the laser interferometer 5 is perpendicular to the incident surface of the optical glass plate 2, or the point where the laser emitted by the laser interferometer 5 is perpendicular to the incident surface of the optical glass plate 2 is rotated clockwise or counterclockwise around the Z axis or the X axis by an initial angle γ.

[0083] Furthermore, the range of the initial angle γ is 0°≤γ<90°, and 0° is the position when the laser is vertically incident on the optical glass plate.

[0084] Furthermore, the motion generating device 4 drives the optical glass plate 2 to rotate clockwise or counterclockwise around the Z axis or the X axis from the initial position by a specified angle β or to move along the X axis from the initial position by a certain displacement.

[0085] Furthermore, the value of the specified angle β or displacement is calculated by substituting the value of the resolution of the laser interferometer to be tested into the formula of the geometric optical path change ΔL generated by the optical glass plate.

[0086] Embodiment 2:

[0087] A method for testing a pm-level displacement resolution of a laser interferometer is implemented based on the pm-level displacement resolution testing device of a laser interferometer described in Example 1, and includes the following steps:

[0088] Insert an optical glass plate into the measuring optical path, set the initial position of the optical glass plate to be the point where the laser interferometer emits laser light perpendicular to the incident surface of the optical glass plate, or rotate the point where the laser interferometer emits laser light perpendicular to the incident surface of the optical glass plate clockwise or counterclockwise around the Z axis or X axis by an initial angle γ;

[0089] Start the laser interferometer light source, and the laser interferometer emits laser to the measuring optical path;

[0090] The laser beam in the measuring optical path is transmitted through the optical glass plate, hits the fixed reflector and returns to the interferometer along the original path after being reflected, and interferes with the reference light inside the interferometer.

[0091] Control the motion generating device to drive the optical glass plate to rotate a specified angle or move a specified displacement and monitor whether the rotation angle or motion displacement of the motion generating device is correct through a standard device, and the value of the specified angle β or displacement is based on the value detected by the standard device;

[0092] Observe the displacement change information output by the laser interferometer, and compare it with the geometric optical path change ΔL caused by rotating or moving the optical glass plate. If the displacement change information output by the laser interferometer and ΔL are the same step signal, it indicates that the displacement resolution of the laser interferometer reaches ΔL.

[0093] Furthermore, when the optical glass plate is a parallel optical glass plate, assuming that the thickness of the parallel optical glass plate is d, the length is r, the parallelism is α, and the initial position of the parallel optical glass plate is such that the laser is vertically incident on the parallel optical glass plate, the expression for measuring the optical path L of the laser is:

[0094] L=2n1L1+2n2d

[0095] Where n1 is the refractive index of the measuring environment, n2 is the refractive index of the parallel optical glass plate, and L1 is the geometric length of the optical path of the laser except the optical path in the parallel optical glass plate;

[0096] When the parallel optical glass plate is rotated by a specified angle β, the expression of the optical path L′ of the laser light after the rotation is:

[0097] L′=2n1(L1-δ)+2n2(d+δ)

[0098] Wherein, δ is the optical path length of the laser beam in the parallel optical glass plate increased by the rotation of the parallel optical glass plate;

[0099] Therefore, the expression of the optical path ΔL' increased by the rotating parallel optical glass plate in the measuring optical path laser is:

[0100] ΔL'=2(n2-n1)δ

[0101] The expression of δ is:

[0102]

[0103] Where x0 is the distance from the center of the laser beam to one side of the parallel optical glass plate, 0<x0<r;

[0104] Substituting the formula of δ into the optical path increase of the laser in the measuring optical path caused by rotating the parallel optical glass plate, we get:

[0105]

[0106] Then the geometric optical path change ΔL caused by rotating the parallel optical glass plate is:

[0107]

[0108] The parallel optical glass plate is set to K9 glass, the environment is the standard laboratory environment, the glass plate thickness is 10mm, the length is 50mm, the parallelism is 5 arc seconds, and the rotation angle is 100 arc seconds. In this case, the effect of the change in the center position of the beam on the change in the optical path achieved by rotation is as follows Figure 7 As shown by Figure 7 It can be seen that the change of the center position of the beam in the range of 0-50 mm has only an effect of 10 -13 m level, which can meet the resolution test requirements of all ultra-high precision laser interferometers currently on the market.

[0109] The beam position is taken as the center position of the parallel optical glass plate, the optical glass plate is K9 glass, the environment is the standard laboratory environment, the glass plate thickness is 10 mm, the length is 50 mm, the parallelism is 5 arc seconds, and the rotation angle is 100 arc seconds. The influence of the parallelism (0-20 arc seconds) and the rotation angle (0-100 arc seconds) of the parallel optical glass plate on the change of the optical path achieved by rotation is shown in the figure. Figure 8 As shown by Figure 8 It can be seen that it is possible to achieve tiny optical path changes from pm level to nm level, which can meet the pm level displacement resolution test requirements of ultra-high precision laser interferometers.

[0110] Embodiment 3:

[0111] The difference between this embodiment and embodiment 2 is that the rotation method of the motion generating device in this embodiment is changed to rotation around the X axis, and the other operations and calculations are unchanged. Figure 4 shown.

[0112] Embodiment 4:

[0113] The difference between this embodiment and embodiment 2 is that, in this embodiment, the point where the emitted laser of the laser interferometer is perpendicular to the incident surface of the optical glass plate is used as the circle point to rotate clockwise or counterclockwise around the Z axis by an initial angle γ.

[0114] Furthermore, when the initial position of the parallel optical glass plate is a point where the emitted laser of the laser interferometer is perpendicular to the incident surface of the optical glass plate and rotates clockwise or counterclockwise around the Z axis or X axis at an initial angle γ, the expression for measuring the optical path laser L is:

[0115] L=2n1L1+2n2d

[0116] Where n1 is the refractive index of the measuring environment, n2 is the refractive index of the parallel optical glass plate, and L1 is the geometric length of the optical path of the laser except the optical path in the parallel optical glass plate;

[0117] When the parallel optical glass plate is rotated by a specified angle β, the expression of the optical path L′ of the laser light after the rotation is:

[0118] L′=2n1(L1-δ)+2n2(d+δ)

[0119] Wherein, δ is the optical path length of the laser beam in the parallel optical glass plate increased by the rotation of the parallel optical glass plate;

[0120] Therefore, the expression of the optical path ΔL' increased by the rotating parallel optical glass plate in the measuring optical path laser is:

[0121] ΔL'=2(n2-n1)δ

[0122] The expression of δ is:

[0123]

[0124] Substituting the formula of δ into the optical path increase of the laser in the measuring optical path caused by rotating the parallel optical glass plate, we get:

[0125]

[0126] Then the geometric optical path change ΔL caused by rotating the parallel optical glass plate is:

[0127]

[0128] Embodiment 5:

[0129] The difference between this embodiment and embodiment 4 is that the rotation method of the motion generating device in embodiment 4 is changed to rotation around the X-axis, and the other operations and calculations remain unchanged;

[0130] Embodiment 6:

[0131] The difference between this embodiment and embodiment 2 is that when the optical glass plate is a wedge-shaped optical glass plate, θ is the wedge angle of the wedge-shaped optical glass plate, and the initial position of the wedge-shaped optical glass plate is such that the laser is vertically incident on the surface of the wedge-shaped optical glass plate that is perpendicular to the Y axis, the geometric optical path change ΔL″ generated by moving the wedge-shaped optical glass plate is:

[0132]

[0133] Wherein, n1 is the refractive index of the measuring environment, n'2 is the refractive index of the wedge-shaped optical glass plate, and s is the displacement of the wedge-shaped optical glass plate.

[0134] In summary, the present invention provides a laser interferometer pm level displacement resolution test device and measurement method, the test object includes all laser interferometer mechanisms including the interferometer mirror group, and changes the optical path of the light beam on the measuring arm through a motion generating device, so that the phase shift introduced by the angle change from arc seconds to hundreds of arc seconds is equivalent to the phase shift introduced by the nm to pm level displacement in the laser interferometer. The device has a simple structure and is easy to operate, and the interference of Abbe error on the resolution test during the movement is avoided, the test accuracy of the resolution is improved, and the pm level displacement resolution of the laser interferometer can be more effectively evaluated.

[0135] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0136] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0137] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A laser interferometer pm level displacement resolution test device, characterized in that: It comprises a fixed reflector (1), an optical glass plate (2), a connecting shaft (3), a motion generating device (4), and a standard device (6); The fixed reflector (1) is used to reflect the laser light transmitted through the optical glass plate (2) in the measuring light path, so that the reflected laser light returns to the laser interferometer (5) along the original path; The optical glass plate (2) is mounted on the connecting shaft (3) of the motion generating device (4); the optical glass plate (2) is located on the measuring optical path between the laser interferometer (5) and the fixed reflector (1); the geometric center of the optical glass plate (2) is located on the extension line of the connecting shaft of the motion generating device (4); and one side of the optical glass plate (2) is perpendicular to the connecting shaft (3); The motion generating device (4) is used to control the connecting shaft (3) to drive the optical glass plate (2) to rotate a specified angle or move a specified displacement; The standard device (6) is placed opposite to the motion generating device (4), and the standard device (6) is used to measure the true value of the angle or displacement generated by the motion generating device (4); The emitted laser light of the laser interferometer (5) is transmitted through the optical glass plate (2), then incident on the fixed reflector (1) and reflected back to the laser interferometer (5) along the original path, and the reflected laser light interferes with the reference light inside the laser interferometer (5); Set the direction of the measuring optical path to the Y axis, the X axis and the Y axis form a horizontal plane, and the Z axis is perpendicular to the horizontal plane; The initial position of the optical glass plate (2) is when the laser emitted by the laser interferometer (5) is perpendicular to the incident surface of the optical glass plate (2), or the point where the laser emitted by the laser interferometer (5) is perpendicular to the incident surface of the optical glass plate (2) is rotated clockwise or counterclockwise around the Z axis or the X axis by an initial angle γ.

2. The laser interferometer pm level displacement resolution test device according to claim 1, characterized in that: The range of the initial angle γ is 0°≤γ<90°, and 0° is the position when the laser is vertically incident on the optical glass plate (2).

3. The laser interferometer pm level displacement resolution test device according to claim 2, characterized in that: The motion generating device (4) drives the optical glass plate (2) to rotate clockwise or counterclockwise around the Z axis or the X axis from the initial position by a specified angle β or to move along the X axis from the initial position by a certain displacement.

4. The laser interferometer pm level displacement resolution test device according to claim 3, characterized in that: The value of the specified angle β or displacement is calculated by substituting the value of the resolution of the laser interferometer to be tested into the formula of the geometric optical path change ΔL generated by the optical glass plate.

5. A method for testing a pm-level displacement resolution of a laser interferometer, implemented by a pm-level displacement resolution testing device of a laser interferometer according to any one of claims 1 to 4, characterized in that: The steps include: Insert an optical glass plate into the measuring optical path, set the initial position of the optical glass plate to be the point where the laser interferometer emits laser light perpendicular to the incident surface of the optical glass plate, or rotate the point where the laser interferometer emits laser light perpendicular to the incident surface of the optical glass plate clockwise or counterclockwise around the Z axis or X axis by an initial angle γ; Start the laser interferometer light source, and the laser interferometer emits laser to the measuring optical path; The laser beam in the measuring optical path passes through the optical glass plate, hits the fixed reflector, and then returns to the interferometer along the original path after being reflected, interfering with the reference light inside the interferometer. Control the motion generating device to drive the optical glass plate to rotate a specified angle or move a specified displacement and monitor whether the rotation angle or motion displacement of the motion generating device is correct through a standard device, and the value of the specified angle β or displacement is based on the value detected by the standard device; Observe the displacement change information output by the laser interferometer, and compare it with the geometric optical path change ΔL caused by rotating or moving the optical glass plate. If the displacement change information output by the laser interferometer and ΔL are the same step signal, it indicates that the displacement resolution of the laser interferometer reaches ΔL.

6. The method for testing the pm-level displacement resolution of a laser interferometer according to claim 5, characterized in that: When the optical glass plate is a parallel optical glass plate, assuming that the thickness of the parallel optical glass plate is d, the length is r, the parallelism is α, and the initial position of the parallel optical glass plate is such that the laser is incident vertically on the parallel optical glass plate, the expression for measuring the optical path L of the laser is: L=2n1L1+2n2d Where n1 is the refractive index of the measuring environment, n2 is the refractive index of the parallel optical glass plate, and L1 is the geometric length of the optical path of the laser except the optical path in the parallel optical glass plate; When the parallel optical glass plate is rotated by a specified angle β, the expression of the optical path L′ of the laser light after the rotation is: L′=2n1(L1-δ)+2n2(d+δ) Wherein, δ is the optical path length of the laser beam in the parallel optical glass plate increased by the rotation of the parallel optical glass plate; Therefore, the expression of the optical path ΔL' increased by the rotating parallel optical glass plate in the measuring optical path laser is: ΔL'=2(n2-n1)δ The expression of δ is: Where x0 is the distance from the center of the laser beam to one side of the parallel optical glass plate, 0<x0<r; Substituting the formula of δ into the optical path increase of the laser in the measuring optical path caused by rotating the parallel optical glass plate, we get: Then the geometric optical path change ΔL caused by rotating the parallel optical glass plate is:

7. The method for testing the pm-level displacement resolution of a laser interferometer according to claim 6, characterized in that: When the initial position of the parallel optical glass plate is the point where the laser interferometer's emitted laser is perpendicular to the incident surface of the optical glass plate and rotates clockwise or counterclockwise around the Z axis or X axis at an initial angle γ, the expression for measuring the optical path laser's optical path L is: L=2n1L1+2n2d Where n1 is the refractive index of the measuring environment, n2 is the refractive index of the parallel optical glass plate, and L1 is the geometric length of the optical path of the laser except the optical path in the parallel optical glass plate; When the parallel optical glass plate is rotated by a specified angle β, the expression of the optical path L′ of the laser light after the rotation is: L′=2n1(L1-δ)+2n2(d+δ) Where δ is the optical path length of the laser beam in the parallel optical glass plate increased by the rotation of the glass plate; Therefore, the expression of the optical path ΔL' increased by the rotating parallel optical glass plate in the measuring optical path laser is: ΔL'=2(n2-n1)δ The expression of δ is: Substituting the formula of δ into the optical path increase of the laser in the measuring optical path caused by rotating the parallel optical glass plate, we get: Then the geometric optical path change ΔL caused by rotating the parallel optical glass plate is:

8. The method for testing the pm-level displacement resolution of a laser interferometer according to claim 5, characterized in that: When the optical glass plate is a wedge-shaped optical glass plate, θ is the wedge angle of the wedge-shaped optical glass plate, and the initial position of the wedge-shaped optical glass plate is such that the laser is incident vertically on the surface of the wedge-shaped optical glass plate perpendicular to the Y axis, the geometric optical path change ΔL″ caused by moving the wedge-shaped optical glass plate is: Wherein, n1 is the refractive index of the measuring environment, n'2 is the refractive index of the wedge-shaped optical glass plate, and s is the displacement of the wedge-shaped optical glass plate.

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