Michelson interferometer based on reflector angle self-adjustment

Abstract

The invention relates to the technical field of interferometers, in particular to a Michelson interferometer based on reflector angle self-adjustment and a reflector angle compensation adjustment method. The reflector angle compensation adjustment method comprises the following steps: acquiring an interference fringe image of a measured surface in real time; analyzing characteristic parameters of the interference fringe image in real time; the characteristic parameters comprise the number, the phase, the density, the angle or the aberration of the fringes; calculating a difference value between the characteristic parameter and a preset standard characteristic parameter; generating a corresponding first adjusting instruction according to the difference value; executing a corresponding adjusting action according to the first adjusting instruction; the adjustment action comprises adjustment of the position or angle of the reflector. The scheme provided by the invention can be used for solving the problems of low reflector angle adjustment precision, low adjustment efficiency and weak instrument anti-interference capability in the use process of the existing Michelson interferometer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of interferometer, in particular to a Michelson interferometer based on mirror angle self-adjustment and a mirror angle compensation adjustment method. BACKGROUND

[0002] The Michelson interferometer is a classic optical interferometer, which has been widely used in science, engineering and teaching. Its structure is simple, but the principle is clear, which is the basis of many modern interferometers (such as Fourier transform infrared spectrometer), and the measured object has no mechanical contact, which is suitable for the detection of precision optical elements or fragile samples.

[0003] In the field of precision optical detection, such as semiconductor wafer flatness detection and optical lens surface error measurement, the optical axis alignment accuracy is required to reach microns. When the mirror angle is adjusted manually, the experience difference of the operator easily leads to an angle error of more than ±0.01°, which further causes the stripe to shift more than 1 μm, affecting the reliability (precision and reliability) of the detection data, and it is difficult to meet the detection requirements of high efficiency and high precision. SUMMARY

[0004] The purpose of the embodiments of the present application is to provide a Michelson interferometer based on mirror angle self-adjustment and a mirror angle compensation adjustment method, so as to solve the problems of low adjustment accuracy, low adjustment efficiency and weak anti-interference ability of the existing Michelson interferometer in use.

[0005] To achieve the above objectives, this application discloses a Michelson interferometer based on self-adjusting mirror angle. The Michelson interferometer includes: a laser source for providing coherent light; a beam splitter for splitting the coherent light emitted from the laser source into a first beam and a second beam, respectively directing the first beam and the second beam to a mirror and the measured surface of a target workpiece; wherein the first beam and the second beam have similar intensities; a mirror facing the beam splitter for reflecting the first beam back to the beam splitter; and a fixture facing the beam splitter for fixing the target workpiece so that the measured surface of the target workpiece faces the beam splitter. Ideally, the second beam, after illuminating the measured surface, will be reflected back into the beam splitter and merge with the first beam reflected back to the beam splitter. The system generates interference and forms interference light; an adjustment component, connected to the reflector, is used to execute corresponding adjustment actions according to a first adjustment command sent by the intelligent control unit; the adjustment actions include adjusting the angle of the reflector; a detector, facing the beam splitter, is used to acquire interference fringe images of the interference light in real time; the intelligent control unit, connected to both the detector and the adjustment component, is used to acquire the interference fringe images acquired by the detector in real time and analyze the feature parameters of the interference fringe images in real time; and to calculate the difference between the feature parameters and preset standard feature parameters; and to generate a corresponding first adjustment command based on the difference and send the first adjustment command to the adjustment component; the feature parameters include the number, phase, density, angle, or aberration of the fringes.

[0006] Based on the first aspect, in the embodiments of this application, the Michelson interferometer further includes a compensation plate, which is disposed between the beam splitter and the reflector. The compensation plate is made of the same material and has the same thickness as the beam splitter, except that it is not coated with a semi-reflective film.

[0007] Based on the first aspect, in this embodiment of the application, the adjusting component includes: a precision adjusting push rod with built-in stacked PZT piezoelectric ceramics; an adjusting frame, the adjusting frame including a fixed frame and a movable plate; the movable plate is used to fix the reflector, the fixed frame is used to fix the precision adjusting push rod; the telescopic end of the precision adjusting push rod is disposed facing the surface of the movable plate, and the telescopic end of the precision adjusting push rod abuts against the movable plate; the movable plate is rotatably connected to the fixed frame.

[0008] Based on the first aspect, in the embodiments of this application, the detector includes a CCD camera, which is wired or wirelessly connected to the intelligent control unit.

[0009] Based on the first aspect, in this embodiment of the application, the Michelson interferometer further includes a temperature sensor connected to an intelligent control unit. The temperature sensor is used to acquire the real-time temperature of the environment where the beam splitter is located. The intelligent control unit is also used to generate a corresponding second adjustment command based on the real-time temperature and its change, and send the second adjustment command to the adjustment component. The adjustment component is also used to perform a corresponding adjustment action based on the second adjustment command sent by the intelligent control unit. The adjustment action includes adjusting the angle of the reflector.

[0010] Secondly, this application provides a mirror angle compensation adjustment method applicable to the aforementioned Michelson interferometer. The mirror angle compensation adjustment method includes: acquiring an interference fringe image of the measured surface in real time; analyzing the feature parameters of the interference fringe image in real time; the feature parameters include the number, phase, density, angle, or aberration of the fringes; calculating the difference between the feature parameters and preset standard feature parameters; generating a corresponding first adjustment command based on the difference; and executing a corresponding adjustment action based on the first adjustment command; the adjustment action includes adjusting the position or angle of the mirror.

[0011] Based on the second aspect, in the embodiments of this application, the method for obtaining the standard feature parameters includes: using a high-precision standard mirror to replace the measured surface of the target workpiece, obtaining a standard interference fringe image, and analyzing the standard feature parameters of the standard interference fringe image; the fringes in the standard interference fringe image are parallel equally spaced fringes or the standard interference fringe image contains zero-order bright and dark fringes.

[0012] Based on the second aspect, in this embodiment of the application, the first adjustment command includes the direction to be compensated for by the reflector and the angle to be compensated for by the reflector; the step of generating the corresponding adjustment command based on the difference includes: obtaining the fringe offset direction and fringe offset amount of the interference fringe image compared to the standard interference fringe image, and determining the direction to be compensated for by the reflector and the angle to be compensated for by the reflector based on the fringe offset direction, fringe offset amount and known optical path parameters; wherein, the calculation formula for the angle compensation amount of the reflector is as follows: θ=ΔS*λ / 2L; in the above formula, θ represents the angle to be compensated for by the reflector; ΔS represents the fringe offset amount; λ represents the laser wavelength; L represents the distance from the reflector to the beam splitter.

[0013] Based on the second aspect, in the embodiments of this application, the method for adjusting the angle of the reflector further includes: acquiring the real-time temperature of the environment where the beam splitter is located; generating a corresponding second adjustment command based on the real-time temperature and its change; and executing a corresponding adjustment action based on the second adjustment command; the adjustment action includes adjusting the angle of the reflector.

[0014] Based on the second aspect, in the embodiments of this application, the second adjustment command includes the direction to be compensated for by the reflector and the angle to be compensated for by the reflector; the step of generating the corresponding second adjustment command according to the real-time temperature and the temperature change includes: obtaining the fringe offset direction of the interference fringe image compared to the standard interference fringe image, determining the direction of the angle to be compensated for by the reflector according to the fringe offset direction; and adjusting the angle of the reflector according to the preset size when the temperature change reaches a preset value within a preset temperature range.

[0015] The solution provided in this application has at least the following beneficial effects: The Michelson interferometer based on self-adjusting mirror angle provided in this application requires no manual intervention in the mirror angle adjustment process, reducing interference from the human body (such as air disturbances and body temperature). Simultaneously, based on a high-precision adjustment component structure (with a built-in stacked PZT piezoelectric ceramic precision adjustment push rod) and a high-precision closed-loop control algorithm (PID), the mirror can respond quickly and accurately (the Michelson interferometer provided in this application can control the mirror angle error within ±0.005°, adaptable to micro-nano level detection requirements). The detector can acquire accurate interference fringe images in a timely manner, effectively improving the detection efficiency and accuracy of the Michelson interferometer, saving time and effort.

[0016] The mirror angle compensation adjustment method provided in this application uses different characteristic parameters of standard interference fringe images as target references according to different detection objects and detection contents, providing the necessary conditions for realizing closed-loop control. In addition, to cope with temperature interference, whether the change in ambient temperature exceeds a preset value is used as the trigger condition for the action of the adjustment component, which has the effect of advance correction, effectively reducing or eliminating temperature-induced delay interference and ensuring the accuracy of real-time interference fringe data.

[0017] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings: Figure 1 The schematic diagram illustrates the layout of the core components of the Michelson interferometer in the embodiment; Figure 2 The schematic diagram illustrates the structure of the adjusting element in the embodiment; Figure 3 The schematic diagram illustrates the connection points of the precision adjustment push rod, the fixed frame, and the moving plate in the embodiment.

[0019] Explanation of reference numerals in the attached figures 1. Laser source; 2. Beam splitter; 3. Reflector; 4. Adjustment component; 41. Precision adjustment push rod; 42. Fixing frame; 43. Moving plate; 5. Detector; 6. Intelligent control unit; 7. Compensation plate; 100. Target workpiece. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0023] Example 1

[0024] This embodiment provides a Michelson interferometer based on self-adjusting mirror angle. The Michelson interferometer includes a laser source 1, a beam splitter 2, a mirror 3, a fixing component, an adjusting component 4, a detector 5, and an intelligent control unit 6. Figure 1 As shown.

[0025] Laser source 1 can provide light waves with good coherence (i.e., coherent light). In addition to laser source 1, sodium lamps, mercury lamps, etc. can also be used as substitutes.

[0026] Beam splitter 2 is used to split the coherent light emitted by laser source 1 into a first beam and a second beam, and send the first beam and the second beam to the reflector 3 and the measured surface of the target workpiece 100, respectively; wherein the intensity of the first beam and the second beam are similar. Specifically, beam splitter 2 is a semi-transparent and semi-reflective mirror, which allows part of the light to be transmitted and the other part to be reflected, forming two independent optical paths (reference optical path and measurement optical path).

[0027] Reflector 3, facing beam splitter 2, is used to reflect the first beam (reference optical path) back to beam splitter 2. Mounted on a precision guide rail, its movement changes the optical path; the moving distance is directly related to the number of interference fringe changes, and it can be used to measure physical quantities such as length, wavelength, or refractive index.

[0028] The fixing component, facing the beam splitter 2, is used to fix the target workpiece 100, so that the measured surface of the target workpiece 100 faces the beam splitter 2. Ideally, after the second beam (measuring optical path) shines on the measured surface, it will be reflected back into the beam splitter 2, and will merge with the first beam reflected back into the beam splitter 2 to interfere and form interference light.

[0029] Adjustment component 4, connected to the reflector 3, is used to execute corresponding adjustment actions according to the first adjustment command sent by the intelligent control unit 6; the adjustment actions include adjusting the angle of the reflector 3. Specifically, as shown... Figure 2 As shown, the adjusting component 4 includes an adjusting frame and a precision adjusting push rod 41 with built-in stacked PZT piezoelectric ceramics. The precision adjusting push rod 41 has a built-in four-layer stacked PZT piezoelectric ceramic structure and achieves the deflection of the moving mirror around the horizontal / vertical axis through differential voltage driving (driving voltage 0-150V). The adjustment range is ±2°, the angular resolution is 0.001°, and the response time is 0.8ms. There can be one or more precision adjusting push rods 41. The adjusting frame includes a fixed frame 42 and a movable plate 43; the movable plate 43 is used to fix the reflector 3, and the fixed frame 42 is used to fix the precision adjusting push rod 41; the telescopic end of the precision adjusting push rod 41 is positioned facing the surface of the movable plate 43 and abuts against it. When there is only one precision adjusting push rod 41 (i.e., it can only rotate around one axis), the movable plate 43 and the fixed frame 42 can be rotatably connected by a torsion spring or other connecting component; if there are multiple precision adjusting push rods 41, for example, ... Figure 2 As shown, if the reflector 3 is required to rotate simultaneously around the x-axis and y-axis, at least two precision adjustment push rods 41 are needed, and the moving plate 43 and the fixed frame 42 need to meet the requirements of multiple rotational degrees of freedom. In this case, the moving plate 43 and the fixed frame 42 can be connected by a ball joint and elastic element, so that the moving plate 43 can rotate simultaneously around the x-axis and y-axis (as shown in the figure) and automatically reset when not subjected to the pushing force of the precision adjustment push rods 41.

[0030] Specifically, the positional connection relationship between the two precision adjusting push rods 41, the moving plate 43, and the fixing component can be referred to Figure 2 and Figure 3 As shown, the movable plate 43 is provided with fixing holes for accommodating and fixing the reflector 3 (ensuring the stability of the fixing). The radius of the fixing holes is R. The telescopic ends of the two precision adjusting push rods 41 respectively abut against points A1 and A2 of the movable plate 43 (e.g., Figure 3 As shown in the figure, points A1 and A2 are close to two mutually perpendicular adjacent sides of the movable plate 43, and the distances between points A1 and A2 and the center O of the fixing hole are d1 and d2, respectively; the position point where the movable plate 43 is connected to the fixing part is the position of point B in the figure (the position of the ball or ball head pin), and the distances between points A1 and A2 and point B are d3 and d4, respectively; points C1 and C2 are the connection points between two elastic elements (such as springs) and the movable plate 43, respectively. The elastic elements are used to connect the movable plate 43 and the fixing part, and the elastic elements are always in a stretched state, so that the movable plate 43 is always in contact with the telescopic end of the precision adjustment push rod 41. The distances between points C1 and C2 and point B are d5 and d6 respectively; the distance between point B and point O is L; where d1=d2, d3=d4>L, d5=d6, and d3=d4>2R. Based on these positional relationships, the reflector 3 can maintain a high degree of stability and will not vibrate when the moving plate 43 is pushed by one of the precision adjustment push rods 41. Since the distances from the force application points of the two precision adjustment push rods 41 to the center of the fixed hole are the same, and the distances from the force application points of the two precision adjustment push rods 41 to the rotation point (point B) are the same, and the moving plate 43 itself is also an axisymmetric structure (with the line connecting points OB as the axis), it is easier to design control parameters and improve control accuracy when controlling the output force. For example, the precision adjustment push rod 41 corresponding to point A1 is the first precision adjustment push rod, and the precision adjustment push rod 41 corresponding to point A2 is the second precision adjustment push rod. After installation according to the above structure, a voltage P is applied to the first precision adjustment push rod for a duration T, the output end of the first precision adjustment push rod advances by S1, and the moving plate 43 rotates around the x-axis by an angle α1; a voltage P is applied to the second precision adjustment push rod for a duration T, the output end of the first precision adjustment push rod advances by S2, and the moving plate 43 rotates around the y-axis by an angle α2; ideally, S1=S2, α1=α2. If α1≠α2, or the difference between α1 and α2 exceeds the allowable range, then control parameters need to be designed for the first and second precision adjustment push rods respectively according to the correspondence between the applied voltage, duration, and rotation angle, which undoubtedly increases the difficulty of control. Therefore, the adjustment component 4 structure provided in this embodiment can lay a good foundation for realizing the above-mentioned desired situation.

[0031] Detector 5, facing beam splitter 2, is used to acquire interference fringe images of interference light in real time. Specifically, detector 5 includes a CCD camera (pixel size 3.75μm, resolution 1920×1080), installed at the output end of beam splitter 2, and connected to intelligent control unit 6 by wire or wireless means. It is used to transmit the acquired interference fringe images to intelligent control unit 6 in real time, or the CCD camera is connected to the cloud, and the image preprocessing algorithm is used to extract feature parameters such as fringe X / Y axis offset and contrast features (recognition accuracy ±0.1 pixels), and then the feature parameters are transmitted to intelligent control unit 6.

[0032] The intelligent control unit 6 is connected to the detector 5 and the adjustment component 4 respectively. It is used to acquire the interference fringe image collected by the detector 5 in real time and analyze the feature parameters of the interference fringe image in real time; to calculate the difference between the feature parameters and the preset standard feature parameters; and to generate a corresponding first adjustment command based on the difference and send the first adjustment command to the adjustment component 4. The feature parameters include the number, phase, density, angle, or aberration of the fringes. For example, the intelligent control unit 6 can use an ARM Cortex-M7 processor (1.2GHz), integrating three major functional modules: a data acquisition module: synchronously receiving interference fringe images (transmission rate 1Gbps) and environmental sensor data (including temperature, etc.), with a buffer period of 10ms; an algorithm calculation module: built-in image preprocessing algorithm (extracting feature parameters), a fringe-angle conversion model (inputting fringe offset can directly output angle deviation value), a PID angle closed-loop control algorithm, and a scene parameter library (storing angle thresholds and adjustment step sizes for 5 typical measurement scenarios); and a drive output module: outputting a high-precision analog voltage signal to drive the precision adjustment push rod 41, with a voltage resolution of 0.1V, matching the high-precision angle adjustment requirements.

[0033] Furthermore, such as Figure 1 As shown, the Michelson interferometer also includes a compensation plate 7, which is disposed between the beam splitter 2 and the reflector 3. The compensation plate 7 is made of the same material and has the same thickness as the beam splitter 2, except that it is not coated with a semi-reflective film, and its surface is parallel to the beam splitter 2. The compensation plate 7 is mainly used to compensate for the wavefront aberration caused by the different incident angles of the two beams (referring to the two beams that ultimately return to the beam splitter 2 and interfere) passing through the glass of the beam splitter 2, so that the optical path of the tilted light rays is consistent with that of the central light ray. It matches the optical path of the beam on the measured surface in the glass by allowing the beam returning from the reflector 3 to pass through the glass once more, thereby obtaining a high-quality interference fringe pattern.

[0034] Furthermore, the Michelson interferometer also includes an angle sensor connected to the intelligent control unit 6. This angle sensor is used to detect the rotation angle of the moving plate 43 (in multiple directions) in real time and provide real-time feedback to the intelligent control unit 6. Based on the angle sensor, real-time monitoring and feedback of the rotation angle of the moving plate 43 can be achieved. By comparing the feedback value from the angle sensor with the target value (first adjustment command or second adjustment command) issued by the intelligent control unit 6, the working status and execution effect of the precision adjustment push rod 41 can be reflected in real time.

[0035] Furthermore, the Michelson interferometer also includes a temperature sensor connected to the intelligent control unit 6. The temperature sensor is used to acquire the real-time temperature of the environment where the beam splitter 2 is located. The intelligent control unit 6 is also used to generate a corresponding second adjustment command based on the real-time temperature and its change, and send the second adjustment command to the adjustment component 4. The adjustment component 4 is also used to execute a corresponding adjustment action based on the second adjustment command sent by the intelligent control unit 6. The adjustment action includes adjusting the angle of the reflector 3. For example, within the temperature range of -20℃ to 60℃, when the ambient temperature rises from 25℃ to 30℃ (a temperature increase of 5℃), the corresponding precision adjustment push rod 41 is controlled to pre-adjust the angle of the moving plate 43 by 0.015°. The adjustment direction can be determined based on the fringe offset direction of the real-time acquired interference fringe image compared to the standard interference fringe image (if the fringes are offset along the positive X-axis, it means that the adjustable moving mirror needs to be deflected around the negative X-axis (the compensation direction is opposite to the fringe offset direction); the same applies to the Y-axis).

[0036] Example 2

[0037] This embodiment proposes a method for adjusting the angle of a reflector based on Embodiment 1. Specifically, the method for adjusting the angle of a reflector includes the following steps: S1. Real-time acquisition of interference fringe images of the surface under test; S2. Real-time analysis of the feature parameters of the interference fringe image; the feature parameters include the number, phase, density, angle, or aberration of the fringes; S3. Calculate the difference between the feature parameters and the preset standard feature parameters; S4. Generate a corresponding first adjustment command based on the difference; S5. Execute the corresponding adjustment action according to the first adjustment command; the adjustment action includes adjusting the position or angle of the reflector 3.

[0038] The above steps S1 can be completed by the detector 5 (CCD camera) in Embodiment 1, steps S2 to S4 can be completed by the intelligent control unit 6 in Embodiment 1, and S5 can be completed by the adjustment component 4 in Embodiment 1.

[0039] Specifically, the standard feature parameters in step S3 above need to be obtained in advance, and the methods for obtaining them include: A high-precision standard mirror is used to replace the measured surface of the target workpiece 100 to obtain a standard interference fringe image, and the standard feature parameters of the standard interference fringe image are analyzed; the fringes in the standard interference fringe image are parallel equally spaced fringes or the standard interference fringe image contains zero-order bright and dark fringes.

[0040] Because the measurement core differs for different objects being measured (wafers, thin films, components), the core features (standard feature parameters) of the standard interference fringe image will also vary (e.g., surface shape measurement requires "parallel equidistant fringes," while length measurement requires "zero-order bright and dark fringes"). For example: 1) When the characteristic parameter includes phase, the zero-point phase needs to be defined first. The determination process is as follows: Use a high-precision standard mirror to replace the measured surface of the target workpiece 100; drive the PZT to move the reflector 3, passing through at least one wavelength (2π phase), and obtain the corresponding interferogram; for each pixel in the obtained interferogram, its light intensity changes with the PZT position in a sinusoidal curve, and the initial phase of this curve is fitted by an algorithm; finally, define the average (initial) phase of the entire field of view or the (initial) phase of a specified point as zero (or a fixed value), and record the corresponding PZT voltage. In all subsequent measurements, efforts should be made to maintain the phase of this point unchanged, and any fluctuations in the measured object are deviations relative to this "zero surface (point)".

[0041] 2) When characteristic parameters include fringe density / angle, they can be manually set according to the measurement task. For example, based on experience or the estimated degree of fluctuation of the measured object, the number of fringes needed to cover the entire field of view can be determined (e.g., 3 fringes provide moderate sensitivity, while 10 fringes are more sensitive to small changes). By fine-tuning the tilt of mirror 3 until fringes with the desired density and direction appear in the real-time interference fringe image, the current interference fringe image is analyzed to calculate its spatial frequency (X, Y directions) and angle, and these values ​​are set as set points (standard characteristic parameters). That is, the measurement's "sensitivity" and "observation direction" are set, and the closed-loop system will maintain this sensitivity unchanged.

[0042] 3) When characteristic parameters include aberrations, it is necessary to determine the Zernike coefficients. The acquisition process is as follows: A high-precision standard mirror is fixed to a fixture as the "object under test"; a series of independent and complete measurements are performed within a short period (usually 5-20 times or more); the results of multiple measurements are averaged to obtain a set of Zernike coefficients (such as Z4 defocus, Z5 / Z6 astigmatism, etc.). These coefficients represent the repeatable systematic error constituted by the interferometer and the standard mirror; this set of coefficients is set as the target value for closed-loop control. The specific operating steps include: adjusting the interferometer to align the high-precision standard mirror with the cat's-eye point and confocal point of the reflecting mirror 3 to ensure optical path collimation; finely adjusting the angle of the reflecting mirror 3 to produce a moderate number of clear interference fringes; controlling the PZT to drive the reflecting mirror 3 to perform precise stepping (such as 5, 7, or 13 phase shifts), and acquiring an interferogram at each step; using a phase-shifting algorithm to calculate a surface deviation map (usually in nanometers or wavelengths) representing the measurement result of the interferogram; after completing one measurement, without making any adjustments to the high-precision standard mirror or interferometer, directly starting the next measurement; repeating multiple times to obtain multiple surface deviation maps; performing pixel-by-pixel averaging on multiple surface deviation maps to obtain an average system error map; performing mathematical analysis (such as Zernike polynomial fitting) on ​​this average system error map to obtain a set of stable and repeatable Zernike coefficients. This set of Zernike coefficients extracted from the average system error map can be set as the target value (standard characteristic parameter) for closed-loop control. When the Michelson interferometer starts working, its real-time measured Zernike coefficients will be compared with this target value. Any deviation (caused by temperature drift, vibration, etc.) will be identified, and the control system will immediately drive the reflector 3 to compensate, so that the coefficient returns to the preset target state, thereby dynamically stabilizing the entire system in the optimal state at the time of calibration.

[0043] Specifically, the first adjustment command in step S4 above includes the direction to be compensated for by the reflector 3 and the angle to be compensated for by the reflector 3; generating the corresponding adjustment command based on the difference includes: Obtain the fringe offset direction and fringe offset amount of the interference fringe image compared to the standard interference fringe image, and determine the direction and angle of compensation required for the reflector 3 based on the fringe offset direction, fringe offset amount and known optical path parameters; The formula for calculating the angle compensation of the reflector 3 is as follows: θ=∆S*λ / 2L In the above formula, θ represents the angle that the reflector 3 needs to compensate for (unit: rad); ∆S represents the fringe offset (unit: μm); λ represents the laser wavelength (632.8nm); and L represents the distance from the reflector 3 to the beam splitter 2 (unit: mm).

[0044] The direction that the reflector 3 needs to compensate for (i.e., the adjustment direction of the reflector 3) can be referred to in Embodiment 1, and will not be repeated here. Furthermore, the method for adjusting the angle of the reflector 3 also includes: T1. Obtain the real-time temperature of the environment where beam splitter 2 is located; T2. Generate a corresponding second adjustment command based on the real-time temperature and its change. T3. Execute the corresponding adjustment action according to the second adjustment command; the adjustment action includes adjusting the angle of the reflector 3.

[0045] Specifically, the second adjustment command mentioned in step T2 includes the direction to be compensated for by the reflector 3 and the angle to be compensated for by the reflector 3; generating the corresponding second adjustment command based on the real-time temperature and temperature change includes: The direction of the fringe offset of the interference fringe image compared to the standard interference fringe image is obtained, and the direction of the angle to be compensated by the reflector 3 is determined based on the fringe offset direction; for details, please refer to the description in Example 1, which will not be repeated here.

[0046] Within a preset temperature range, when the temperature change reaches a preset value, the angle of the reflector 3 is adjusted according to the preset value. For example, within a temperature range of -20℃ to 60℃, when the ambient temperature rises from 25℃ to 30℃ (a 5℃ increase), the angle of the corresponding precision adjustment push rod 41 is controlled to pre-adjust the moving plate 43 by 0.015°. When the temperature changes, the resulting interference will eventually be reflected in the interference fringe image. However, since temperature interference is usually delayed, the interference fringe image may not have yet produced significant fluctuations when the temperature changes. Therefore, in this embodiment, whether the change in ambient temperature exceeds a preset value is used as the trigger condition for the action of the adjustment component 4, which can achieve an advance correction effect. This can effectively reduce or avoid temperature-induced delayed interference, prevent large shifts or fluctuations in the fringes, and ensure the accuracy of real-time interference fringe data.

[0047] Example 3

[0048] In this embodiment, the parameter configuration of the Michelson interferometer assembled and designed using the structure and method provided in Embodiments 1 and 2 above is as follows: Laser source 1: Output wavelength 632.8nm, power adjustable from 5-20mW, divergence angle 0.2mrad, light intensity fluctuation ≤±1%; Beam splitter 2: 45° beam splitting surface, transmittance / reflectance = 50% / 50%, light transmission aperture 20mm, refractive index 1.5168; Reflector 3: Dimensions 20×20mm, flatness λ / 20 (λ=632.8nm), rigidly connected to the piezoelectric ceramic regulator; PZT piezoelectric ceramic: Four layers of PZT stacked, adjustment range ±2°, angular resolution 0.001°, response time 0.8ms, driving voltage 0-150V; CCD camera: Pixel size 3.75μm, resolution 1920×1080, frame rate 30fps, image transmission rate 1Gbps; Intelligent Control Unit 6: ARM Cortex-M7 processor, 1.2GHz, algorithm response latency ≤800μs, stores 5 sets of scene parameters.

[0049] The workflow for automatically adjusting the tilt angle of mirror 3 using this Michelson interferometer is as follows: 1) System initialization and calibration phase (time ≤ 60 seconds) The intelligent control unit 6 loads default measurement scene parameters (such as micro-nano measurement mode: angle adjustment step 0.001°, stripe contrast threshold 0.75). Laser source 1 outputs 5mW laser (wavelength 632.8nm), which is incident on the beam splitter to form initial interference fringes; The CCD camera acquires the initial fringe image and calculates characteristic parameters such as the initial fringe offset (if the offset is > 0.5 μm, proceed to the initial angle adjustment process); the initial angle value of the reflector 3 is acquired as the reference zero point; 2) Initial Angle Alignment Process Stripe-Angle Conversion: The intelligent control unit 6 inputs the initial stripe offset of 4.8μm on the X-axis and 3.2μm on the Y-axis. Combined with the optical path parameters (2150mm from the beam splitter to the reflector 3), the required adjustment angle is calculated through the conversion model: 0.012° on the X-axis and 0.008° on the Y-axis. PID drive adjustment: The intelligent control unit 6 outputs the corresponding drive voltage. The precision adjustment push rod 41 on the Y-axis can be extended or shortened to realize the angle adjustment in the X-axis direction (rotation around the X-axis). The precision adjustment push rod 41 on the X-axis can be extended or shortened to realize the angle adjustment in the Y-axis direction (rotation around the Y-axis). The angle sensor provides real-time feedback during the adjustment process. Steady-state judgment: When the CCD detected stripe offset ≤ 0.5μm, the deviation between the angle feedback value and the target value ≤ 0.002°, and this condition is maintained for 500ms, the initial alignment is complete; 3) Real-time angle compensation process Stripe deviation monitoring: The CCD camera periodically acquires stripe images (once every 33ms). If a stripe offset > 0.3μm is detected, angle compensation is immediately triggered. Angle deviation correction: The algorithm recalculates the angle deviation using the new stripe offset, and the PID controller dynamically adjusts the drive voltage. For example, when the stripe X-axis offset is 0.6μm, the output angle compensation is 0.0015°, and the precision adjustment push rod 41 provides fast response adjustment. Environmental compensation: When the temperature sensor detects a temperature change of ≥0.5℃, the angle is adjusted in advance according to the pre-stored compensation coefficient (e.g., if the temperature rises by 2℃, the angle is pre-adjusted by 0.006°) to reduce stripe fluctuations caused by environmental interference. Angle feedback closed loop: The angle sensor transmits the actual angle value back to the control unit in real time, compares it with the target value, and corrects the adjustment amount to ensure compensation accuracy; 4) Scene switching angle adaptation process Component identification: After the measurement component is replaced, the intelligent control unit 6 reads the component ID through the Type-C interface and automatically loads the corresponding scene parameters (such as switching to the thin film measurement scene, changing the angle adjustment step size to 0.003°, and the contrast threshold to 0.7). Rapid calibration: The CCD acquires the initial stripes of a new scene, and the algorithm simplifies the calculation process (extracting only the core stripe features). The angle deviation calculation is completed within 100ms, and the precision adjustment push rod 41 is driven to complete the angle adaptation within 30 seconds without manual intervention.

[0050] Performance verification results: The interferometer provided in this embodiment has high angle adjustment accuracy. Within a temperature range of -20℃ to 60℃, the angle adjustment accuracy is stable at ±0.004°, the angle feedback error is ≤0.002°, the fringe offset is ≤0.4μm, and the angle compensation error corresponding to the fringe offset is ≤0.001°. It has fast closed-loop response speed, with a single initial alignment time of ≤45 seconds, a fringe acquisition period of ≤33ms, an angle deviation calculation delay of ≤200μs, a piezoelectric ceramic drive response time of ≤1ms, and a closed-loop adjustment delay of ≤1.5ms for the entire system. It has strong anti-interference ability. When the environmental vibration amplitude is ≤0.1g, the angle fluctuation control is ≤0.003°, the fringe stability retention rate is ≥98.5%, the X / Y axis offset of the interference fringes after adjustment is ≤0.5μm, the contrast is ≥0.7, the fringe offset increment is ≤0.1μm after 8 hours of continuous operation, the angle drift is ≤0.005°, and the light intensity fluctuation is ≤±0.9%.

[0051] Its core components use mature mass-produced devices. The PZT piezoelectric ceramic and intelligent control unit are highly integrated, with a system failure rate of ≤0.5%. The structure is compact and the cost is controllable. It can be widely used in precision measurement, industrial testing, scientific research experiments and other scenarios, and has significant industrialization prospects.

[0052] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0053] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A Michelson interferometer based on self-adjusting mirror angle, characterized in that, The Michelson interferometer includes: Laser source (1) is used to provide coherent light; The beam splitter (2) is used to split the coherent light emitted by the laser source (1) into a first beam and a second beam, and send the first beam and the second beam to the reflector (3) and the measured surface of the target workpiece (100) respectively; wherein the intensity of the first beam and the second beam is similar. A reflector (3) is positioned facing the beam splitter (2) to reflect the first beam back to the beam splitter (2). The fixing component is set facing the beam splitter (2) to fix the target workpiece (100) so that the measured surface of the target workpiece (100) faces the beam splitter (2); after the second beam shines on the measured surface, it is reflected back into the beam splitter (2) and merges with the first beam reflected back into the beam splitter (2) by the mirror (3), and interference occurs to form interference light; An adjustment component (4) is connected to the reflector (3) and is used to perform a corresponding adjustment action according to a first adjustment command sent by the intelligent control unit (6); the adjustment action includes adjusting the angle of the reflector (3); The detector (5) is set facing the beam splitter (2) for real-time acquisition of interference fringe images of the interference light; The intelligent control unit (6) is connected to the detector (5) and the adjustment component (4) respectively. It is used to acquire the interference fringe image collected by the detector (5) in real time and analyze the feature parameters of the interference fringe image in real time; and to calculate the difference between the feature parameters and the preset standard feature parameters; and to generate the corresponding first adjustment command according to the difference and send the first adjustment command to the adjustment component (4); the feature parameters include the number of fringes, phase, density, angle or aberration.

2. The Michelson interferometer according to claim 1, characterized in that, The Michelson interferometer also includes a compensation plate (7), which is located between the beam splitter (2) and the reflector (3). The compensation plate (7) is made of the same material and has the same thickness as the beam splitter (2), except that it is not coated with a semi-reflective film.

3. The Michelson interferometer according to claim 1, characterized in that, The adjusting element (4) includes: Precision adjustment push rod (41) with built-in stacked PZT piezoelectric ceramic; The adjustment frame includes a fixed frame (42) and a movable plate (43); the movable plate (43) is used to fix the reflector (3), and the fixed frame (42) is used to fix the precision adjustment push rod (41). The telescopic end of the precision adjustment push rod (41) is positioned facing the surface of the moving plate (43), and the telescopic end of the precision adjustment push rod (41) abuts against the moving plate (43); the moving plate (43) is rotatably connected to the fixed frame (42).

4. The Michelson interferometer according to claim 1, characterized in that, The detector (5) includes a CCD camera, which is connected to the intelligent control unit (6) via wired or wireless means.

5. The Michelson interferometer according to claim 1, characterized in that, The Michelson interferometer also includes a temperature sensor connected to the intelligent control unit (6). The temperature sensor is used to obtain the real-time temperature of the environment where the beam splitter (2) is located. The intelligent control unit (6) is also used to generate a corresponding second adjustment command based on the real-time temperature and its change, and send the second adjustment command to the adjustment component (4). The adjustment component (4) is also used to perform a corresponding adjustment action based on the second adjustment command sent by the intelligent control unit (6). The adjustment action includes adjusting the angle of the reflector (3).

6. A method for adjusting the angle of a reflecting mirror, applicable to the Michelson interferometer according to any one of claims 1 to 5, characterized in that, The method for adjusting the angle compensation of the reflector includes: Real-time acquisition of interference fringe images of the surface under test; Real-time analysis of feature parameters of interference fringe images; the feature parameters include the number, phase, density, angle, or aberration of the fringes; Calculate the difference between the feature parameters and the preset standard feature parameters; A corresponding first adjustment command is generated based on the difference; The corresponding adjustment action is executed according to the first adjustment command; the adjustment action includes adjusting the position or angle of the reflector (3).

7. The method for adjusting the angle of a reflector according to claim 6, characterized in that, The method for obtaining the standard feature parameters includes: A high-precision standard mirror is used to replace the measured surface of the target workpiece (100) to obtain a standard interference fringe image, and the standard feature parameters of the standard interference fringe image are analyzed; the stripes in the standard interference fringe image are parallel equally spaced stripes or the standard interference fringe image contains zero-order bright and dark stripes.

8. The method for adjusting the angle of a reflector according to claim 7, characterized in that, The first adjustment command includes the direction to be compensated for by the reflector (3) and the angle to be compensated for by the reflector (3); the step of generating the corresponding adjustment command based on the difference includes: Obtain the fringe offset direction and fringe offset amount of the interference fringe image compared with the standard interference fringe image, and determine the direction and angle of compensation required by the reflector (3) based on the fringe offset direction, fringe offset amount and known optical path parameters; The formula for calculating the angle compensation of the reflector (3) is as follows: ； In the above formula, θ represents the angle that the reflector needs to compensate for; ΔS represents the fringe offset; λ represents the laser wavelength; and L represents the distance from the reflector to the beam splitter.

9. The method for adjusting the angle of a reflector according to claim 7, characterized in that, The method for adjusting the angle of the reflector (3) also includes: Obtain the real-time temperature of the environment where the beam splitter (2) is located; A second adjustment command is generated based on the real-time temperature and its changes. The corresponding adjustment action is executed according to the second adjustment command; the adjustment action includes adjusting the angle of the reflector (3).

10. The method for adjusting the angle of a reflector according to claim 9, characterized in that, The second adjustment command includes the direction to be compensated for by the reflector (3) and the angle to be compensated for by the reflector (3); the generation of the corresponding second adjustment command based on the real-time temperature and temperature change includes: Obtain the fringe offset direction of the interference fringe image compared to the standard interference fringe image, and determine the direction of the angle to be compensated by the reflector (3) based on the fringe offset direction; Within the preset temperature range, when the temperature change reaches the preset value, the angle of the reflector (3) is adjusted according to the preset size.

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