A pm-level displacement resolution test device and method for a laser interferometer

Abstract

A pm-level displacement resolution test device and method for a laser interferometer, belonging to the field of optical measurement technology. It solves the problems that the pm-level displacement resolution of the laser interferometer cannot be measured and is inaccurate. The present invention includes a fixed mirror, an optical glass plate, a connecting shaft, a motion generating device, and a standard. The fixed mirror is used to reflect the laser transmitted through the optical glass plate in the measurement optical path, so that the reflected laser returns along the original path to the laser interferometer. The optical glass plate is installed on the connecting shaft of the motion generating device. The optical glass plate is located on the measurement optical path between the laser interferometer and the fixed mirror. 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. The present invention realizes the equivalent phase shift generated by the nm-to-pm-level displacement in the laser interferometer by controlling the movement of the optical glass plate, making the pm-level displacement resolution test of the laser interferometer more sufficient and improving the test accuracy.

Description

Technical Field

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

[0002] Laser interference displacement measurement technology, with its advantages such as high resolution, non-contact, strong anti-interference ability and traceability, is widely used in fields such as ultra-precision machining, microelectronics manufacturing, precision equipment installation and calibration, and large scientific installations, 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 applied in ultra-high-precision measurement and metrology scenarios. Therefore, it is of great significance to conduct a complete, reliable and accurate resolution test on the laser interferometer for the evaluation of the interferometer performance.

[0003] With the progress of technology, various application scenarios such as ultra-precision machining, microelectronics manufacturing, and precision equipment installation have put forward requirements for the measurement resolution of laser interferometers at the nm level, sub-nm level or even pm level. Using a displacement generating device standard to directly evaluate, the unique displacement generating device standard can only evaluate a laser interferometer with a resolution accuracy lower than itself. For example, the P-753 piezoelectric displacement stage of PI company, whose resolution is 0.1 nm, can only evaluate a laser interferometer with a displacement resolution accuracy lower than 0.1 nm, and the installation accuracy requirements for the laser interferometer are relatively high during the evaluation process. Currently, there is a lack of a standard tool that can accurately generate pm-level displacements for the measurement resolution test of laser interferometers.

[0004] Hu Pengcheng of 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-nm level displacement is converted into the phase of the interference signal and then into a mm-level spatial displacement for testing. This scheme can test the light source and signal processing links, avoiding the influence of factors such as environmental fluctuations, Abbe error, and vibration. However, there is no interferometer mirror group during the measurement process, and no interference optical path is formed, so the test of the overall resolution of the interferometer is not sufficient.

[0005] Perform a complete uncertainty analysis of the laser interferometer or compare it with a laser interferometer of the same precision level. For example, in (S. Rene. "Accurate extraction of thermal expansion coefficients and their uncertainties from high precision interferometric length measurements [C]." SPIE Optics Photonics (2005)), the measurement precision and resolution of the laser interferometer are evaluated by assessing various uncertainties during the measurement process. However, it is difficult to determine all uncertain factors with this method. Although the resolution of the interferometer can be accurately evaluated to a certain precision, there are still some deficiencies. Summary of the Invention

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

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

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

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

[0010] The optical glass plate is installed on the connecting shaft of the motion generating device. The optical glass plate is located on the measurement optical path between the laser interferometer and the fixed mirror. 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 values of the angles or displacements 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 mirror and reflected back along the original path to the laser interferometer. The reflected laser interferes with the internal reference light of the laser interferometer;

[0014] Set the direction of the measurement optical path as 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 laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate, or rotates the initial angle γ clockwise or counterclockwise around the Z-axis or X-axis with the point where the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate as the center point.

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

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

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

[0019] A method for testing the pm-level displacement resolution of a laser interferometer is realized relying on the described laser interferometer pm-level displacement resolution testing device, and includes the following steps:

[0020] Insert an optical glass plate into the measurement optical path, and set the initial position of the optical glass plate so that the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate or rotates the initial angle γ clockwise or counterclockwise around the Z-axis or X-axis with the point where the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate as the center point;

[0021] Start the light source of the laser interferometer, and the laser interferometer emits laser light into the measurement optical path;

[0022] The laser light in the measurement optical path passes through the optical glass plate, hits the fixed mirror and is reflected, and then returns to the interferometer along the original path to interfere 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 the motion displacement of the motion generating device is correct through a standard device. The value of the specified angle β or the displacement is based on the value detected by the standard device;

[0024] Observe the displacement change information output by the laser interferometer, and compare the displacement change information output by the laser interferometer with the geometric optical path change ΔL generated 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] Further, when the optical glass plate is a parallel optical glass plate, assuming the thickness of the parallel optical glass plate is d, the length is r, and the parallelism is α, when the initial position of the parallel optical glass plate is such that the laser is perpendicularly incident on the parallel optical glass plate, the expression for the optical path L of the laser in the measurement optical path is:

[0026] L = 2n1L1 + 2n2d

[0027] Where n1 is the refractive index of the measurement 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 for the optical path inside the parallel optical glass plate;

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

[0029] L' = 2n1(L1 - δ) + 2n2(d + δ)

[0030] Where δ is the optical path of the laser beam increased in the parallel optical glass plate after the rotation of the parallel optical glass plate;

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

[0032] ΔL' = 2(n2 - n1)δ

[0033] The expression for 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] After substituting the formula for δ into the increased optical path of the laser in the measurement optical path caused by rotating the parallel optical glass plate, we get:

[0037]

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

[0039]

[0040] Further, when the initial position of the parallel optical glass plate is to rotate an initial angle γ clockwise or counterclockwise around the Z-axis or X-axis with the point where the laser emitted by the laser interferometer is perpendicularly incident on the incident surface of the optical glass plate as the origin, the expression for the optical path L of the laser in the measurement optical path is:

[0041] L = 2n1L1 + 2n2d

[0042] Among them, n1 is the refractive index of the measurement 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 for the optical path length in the parallel optical glass plate;

[0043] When the parallel optical glass plate rotates by a specified angle β, the expression for the optical path L' of the laser in the measurement optical path after rotation is:

[0044] L' = 2n1(L1 - δ) + 2n2(d + δ)

[0045] Among them, δ is the optical path of the laser beam increased in the parallel optical glass plate after the glass plate rotates;

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

[0047] ΔL' = 2(n2 - n1)δ

[0048] The expression for δ is:

[0049]

[0050] After substituting the formula for δ into the increased optical path of the laser in the measurement optical path caused by rotating the parallel optical glass plate, we get:

[0051]

[0052] Then the geometric optical path change ΔL generated 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. When the initial position of the wedge-shaped optical glass plate is such that the laser is perpendicular to the surface of the wedge-shaped optical glass plate perpendicular to the Y-axis, the geometric optical path change ΔL″ generated by moving the wedge-shaped optical glass plate is:

[0055]

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

[0057] Advantages of the present invention:

[0058] A pm-level displacement resolution test device for a laser interferometer according to the present invention. The object of the test device includes all laser interferometer mechanisms including an interferometer mirror group, so that the pm-level displacement resolution of the laser interferometer can be more effectively evaluated. By changing the optical path of the light beam on the measurement arm through a motion generating device, the phase shift introduced by an angular change from arcseconds to hundreds of arcseconds is equivalent to the phase shift introduced by a displacement from nm to pm levels in the laser interferometer. While enhancing the anti-interference ability of the test device, the test accuracy of the resolution is improved.

[0059] A pm-level displacement resolution test device for a laser interferometer according to the present invention reflects the outgoing light using a fixed mirror, and combines a motion generating device with an optical glass plate to change the laser optical path, thereby avoiding the interference caused by Abbe error during the movement of the guide rail to the resolution test; the test device has the characteristics of simple structure and simple operation, and can be directly used for the pm-level displacement resolution test of the laser interferometer without additional adjustment, and is more suitable for the application of the pm-level displacement resolution test of the laser interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0061] Figure 2 is a schematic diagram of the size and beam position of a parallel optical glass plate according to Embodiments 2, 3, 4, and 5 of the present invention;

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

[0063] Figure 4 is a schematic diagram of an implementation manner of a method for a pm-level displacement resolution test device for a laser interferometer according to Embodiment 3 of the present invention;

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

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

[0066] Figure 7 is a diagram showing the influence of the change in the beam center position on the rotation to achieve the change in the optical path in Embodiment 2;

[0067] Figure 8 is a simulation result diagram of a test method for a pm-level displacement resolution test device for a laser interferometer according to Embodiment 2;

[0068] Figure 9 It is a top view of the schematic diagram of the implementation mode of a method for a pm-level displacement resolution test device of a laser interferometer described in Embodiment 6 of the present invention;

[0069] Figure 10 It is a front view of the schematic diagram of the implementation mode of a method for a pm-level displacement resolution test device of a laser interferometer described in Embodiment 6 of the present invention.

[0070] Figure 11 It is a schematic diagram of the size of the wedge-shaped optical glass plate and the beam position described in Embodiment 6 of the present invention. Specific implementation mode

[0071] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation modes. It should be understood that the specific implementation modes described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific implementation modes described are only a part of the implementation modes of the present invention, rather than all of the specific implementation modes. The components of the specific implementation mode of the present invention usually described and shown in the accompanying drawings here can be arranged and designed in various different configurations, and the present invention can also have other implementation modes.

[0072] Therefore, the detailed description of the specific implementation mode of the present invention provided in the accompanying drawings below is not intended to limit the scope of the present invention to be protected, but only represents the selected specific implementation mode of the present invention. All other specific implementation modes obtained by those skilled in the art based on the specific implementation mode of the present invention without creative efforts belong to the scope of protection of the present invention.

[0073] To further understand the content, features and effects of the present invention, the following specific implementation modes are exemplified and are accompanied by the attached Figure 1 - Attached Figure 11 The details are as follows:

[0074] Embodiment 1:

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

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

[0077] The optical glass plate 2 is installed on the connecting shaft 3 of the motion generating device 4. The optical glass plate 2 is located on the measurement optical path between the laser interferometer 5 and the fixed mirror 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 by a specified angle or move by a specified displacement;

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

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

[0081] Set the direction of the measurement optical path as 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 rotates an initial angle γ clockwise or counterclockwise around the Z-axis or the X-axis with the point where the laser emitted by the laser interferometer 5 is perpendicular to the incident surface of the optical glass plate 2 as the center.

[0083] Further, the range of the initial angle γ is 0° ≤ γ < 90°. When it is 0°, it is the position when the laser is perpendicularly incident on the optical glass plate.

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

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

[0086] Embodiment 2:

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

[0088] Insert an optical glass plate into the measurement optical path, set the initial position of the optical glass plate so that the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate, or use the point where the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate as the origin, and rotate the initial angle γ clockwise or counterclockwise around the Z-axis or X-axis;

[0089] Start the laser interferometer light source, and the laser interferometer emits laser light into the measurement optical path;

[0090] The laser in the measurement optical path passes through the optical glass plate and hits the fixed mirror, and after reflection, it returns to the interferometer along the original path 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 use the standard device to monitor whether the rotation angle or motion displacement of the motion generating device is correct. The value of the specified angle β or displacement amount is based on the value detected by the standard device;

[0092] Observe the displacement change information output by the laser interferometer, compare the displacement change information output by the laser interferometer with the geometric optical path change ΔL generated 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, assume 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 when the laser is perpendicularly incident on the parallel optical glass plate, the expression for the optical path L of the laser in the measurement optical path is:

[0094] L = 2n1L1 + 2n2d

[0095] Where, n1 is the refractive index of the measurement 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 for the optical path inside the parallel optical glass plate;

[0096] When the parallel optical glass plate rotates a specified angle β, the expression for the optical path L' of the laser in the measurement optical path after rotation is:

[0097] L' = 2n1(L1 - δ) + 2n2(d + δ)

[0098] Where, δ is the optical path of the laser beam in the parallel optical glass plate increased after the rotation of the parallel optical glass plate;

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

[0100] ΔL' = 2(n2 - n1)δ

[0101] The expression for δ is:

[0102]

[0103] Among them, \(x_0\) is the distance from the center of the laser beam to one side of the parallel optical glass plate, and \(0 \lt x_0 \lt r\);

[0104] After substituting the formula of \(\delta\) into the optical path increase of the measurement optical path caused by rotating the parallel optical glass plate, we get:

[0105]

[0106] Then the geometric optical path change \(\Delta L\) generated by rotating the parallel optical glass plate is:

[0107]

[0108] Set the parallel optical glass plate as K9 glass, the environment is the laboratory standard environment, the thickness of the glass plate is 10 mm, the length is 50 mm, the parallelism is 5 arcseconds, and the rotation angle is 100 arcseconds. In this case, the influence of the change in the beam center position on the optical path change realized by rotation is as Figure 7 shown. From Figure 7 it can be seen that when the beam center position changes within the range of 0 - 50 mm, the influence on the optical path change realized by rotating the parallel optical glass plate is only at the order of 10 -13 magnitude, which can meet the resolution test requirements of all ultra-high-precision laser interferometers on the market currently.

[0109] Take the beam position as the center position of the parallel optical glass plate, the optical glass plate is K9 glass, the environment is the laboratory standard environment, the thickness of the glass plate is 10 mm, the length is 50 mm, the parallelism is 5 arcseconds, and the rotation angle is 100 arcseconds. The influence of the parallelism (0 - 20 arcseconds) and rotation angle (0 - 100 arcseconds) of the parallel optical glass plate on the optical path change realized by rotation is as Figure 8 shown. From Figure 8 it can be seen that it can achieve a small optical path change from pm level to nm level, which can meet the pm-level displacement resolution test requirements of ultra-high-precision laser interferometers.

[0110] Example 3:

[0111] The difference between this example and Example 2 is that the rotation method of the motion generating device in this example is changed to rotate around the X-axis, and the rest of the operations and calculations remain unchanged, as Figure 4 shown.

[0112] Example 4:

[0113] The difference between this example and Example 2 is that in this example, the initial angle \(\gamma\) is rotated clockwise or counterclockwise around the Z-axis with the point where the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate as the origin.

[0114] Further, when the initial position of the parallel optical glass plate is rotated clockwise or counterclockwise by an initial angle γ around the Z-axis or X-axis with the point where the laser emitted by the laser interferometer is perpendicular to the incident surface of the optical glass plate as the origin, the expression for the optical path L of the measurement optical path laser is:

[0115] L = 2n1L1 + 2n2d

[0116] where n1 is the refractive index of the measurement 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 for the optical path inside the parallel optical glass plate;

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

[0118] L' = 2n1(L1 - δ) + 2n2(d + δ)

[0119] where δ is the optical path of the laser beam in the parallel optical glass plate increased after the rotation of the parallel optical glass plate;

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

[0121] ΔL' = 2(n2 - n1)δ

[0122] The expression for δ is:

[0123]

[0124] After substituting the formula for δ into the increased optical path of the measurement optical path laser caused by rotating the parallel optical glass plate, we get:

[0125]

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

[0127]

[0128] Example 5:

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

[0130] Example 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. When the initial position of the wedge-shaped optical glass plate is such that the laser is perpendicularly incident on the surface of the wedge-shaped optical glass plate perpendicular to the Y-axis, the geometric optical path change ΔL″ generated by moving the wedge-shaped optical glass plate is:

[0132]

[0133] where n1 is the refractive index of the measurement 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, a laser interferometer pm-level displacement resolution test device and measurement method provided by the present invention have test objects including all laser interferometer mechanisms such as the interferometer mirror group. By changing the optical path of the light beam on the measurement arm through the motion generating device, the phase shift introduced by the angular second to hundred angular second-level angle change is equivalent to the phase shift introduced by the nm to pm-level displacement in the laser interferometer. It has a simple structure and is easy to operate, avoiding the interference of Abbe error on the resolution test during the motion process, improving the test accuracy of the resolution, and being able to more effectively evaluate the pm-level displacement resolution of the laser interferometer.

[0135] Although the present application has been described above with reference to specific embodiments, various improvements can be made to it and components therein can 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 can be combined with each other in any way. The exhaustive description of these combinations is not given in this specification only for the sake of saving space and 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 only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0137] Although the present application has been described above with reference to specific embodiments, various modifications thereof may be made and components 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 features in the specific embodiments disclosed in the present application can be combined with each other in any way, and the exhaustive description of these combinations is not given in this specification only for the sake of saving space and 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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