System and method for measuring parameters of measured object based on single longitudinal mode laser

Abstract

The present invention relates to the field of optical detection technology, and discloses a system and method for measuring the parameters of a measured object based on a single longitudinal mode laser, so as to improve the efficiency and convenience of detection. The system includes: an interference generating device whose light source is a single longitudinal mode laser, an adjuster for changing the optical path in a beam of light waves that causes interference, a scattering plate that presents the interference image generated by the interference generating device, an image collector that takes pictures of the pattern presented by the scattering plate, and a host that communicates data with the image collector. During the measurement process, the change of the interference generating device caused by the initial state and the final state of the measured object replaces the change caused by the adjuster to the optical path difference, and then the reference curve is searched to obtain the difference between the optical path differences corresponding to the initial state and the final state of the measured object, and finally the result of the corresponding parameter of the measured object is obtained according to the difference. Since the optical path difference can be accurately positioned to the nanometer level, the whole process is simple, convenient and high-precision.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and in particular to a system and method for measuring parameters of a measured object based on single longitudinal mode laser. Background Art

[0002] Optical-based detection is widely used in all walks of life. Among the many existing optical detection applications, how to further improve the efficiency and convenience of detection has become a common problem that needs to be solved in all walks of life. Summary of the invention

[0003] The present invention aims to disclose a system and method for measuring parameters of a measured object based on single longitudinal mode laser, so as to improve the efficiency and convenience of detection.

[0004] To achieve the above object, the present invention discloses a system for measuring parameters of an object to be measured based on single longitudinal mode laser, comprising:

[0005] The light source is an interference generating device of a single longitudinal mode laser, and a regulator for changing the optical path is arranged in a beam of light waves generating interference;

[0006] A scattering sheet presenting the interference image generated by the interference generating device;

[0007] An image collector for taking a picture of the pattern presented by the scattering sheet;

[0008] A host computer that performs data communication with the image collector is used to obtain from the image collector a series of speckle images collected by the adjuster in the process of changing the optical path, calculate the gray value curves under different pixel radii in each frame of the speckle image, determine the threshold range of the light intensity corresponding to the intercepted circular ring area according to the maximum gray value, and then determine the pixel radius sizes corresponding to the inner and outer rings of the circular ring area according to the threshold range; then calculate the speckle contrast of the intercepted circular ring area in each frame of the speckle image, calibrate at least three discrete data of the speckle contrast weakening as the optical path difference increases, and fit the speckle contrast within the measurement range according to each discrete data. A reference curve is obtained in which the speckle contrast in a range decreases as the optical path difference increases, and the maximum value of the measurement range is less than or equal to the coherence length of the single longitudinal mode laser; then a speckle picture corresponding to the final state of the measured object after being placed in the interference beam is obtained from the image collector, and the calculated speckle contrast of the final state is compared with the speckle contrast corresponding to the initial state of the measured object before being placed in the interference beam or after being placed in the interference beam, and the reference curve is searched to obtain the difference between the optical path differences corresponding to the initial state and the final state of the measured object, and the result of the corresponding parameter of the measured object is obtained according to the difference;

[0009] The change of the initial state and final state of the measured object on the interference generating device is limited to the change of the optical path difference brought about by replacing the adjuster.

[0010] To achieve the above object, the present invention further discloses a method for measuring parameters of a measured object based on a single longitudinal mode laser, comprising:

[0011] Step S1: deploying a system for measuring parameters of an object to be measured based on a single longitudinal mode laser, the system comprising:

[0012] The light source is an interference generating device of a single longitudinal mode laser, and a regulator for changing the optical path is arranged in a beam of light waves generating interference;

[0013] A scattering sheet presenting the interference image generated by the interference generating device;

[0014] An image collector for taking a picture of the pattern presented by the scattering sheet;

[0015] A host computer that performs data communication with the image collector, the method comprising:

[0016] The host obtains a series of speckle images collected by the regulator in the process of changing the optical path from the image collector, calculates the gray value curves under different pixel radii in each frame of the speckle image, determines the threshold range of the light intensity corresponding to the intercepted circular area according to the maximum gray value, and then determines the pixel radius sizes corresponding to the inner and outer rings of the circular area according to the threshold range; then calculates the speckle contrast of the intercepted circular area in each frame of the speckle image, and calibrates at least three discrete data of the speckle contrast weakening as the optical path difference increases, and fits the speckle contrast within the measurement range according to each discrete data. A reference curve is obtained in which the optical path difference is increased and weakened, and the maximum value of the measurement range is less than or equal to the coherence length of the single longitudinal mode laser; then a speckle picture corresponding to the final state of the measured object after being placed in the interference beam is obtained from the image collector, and the speckle contrast of the final state obtained by calculation is compared with the speckle contrast corresponding to the initial state of the measured object before being placed in the interference beam or after being placed in the interference beam, and the reference curve is searched to obtain the difference between the optical path differences corresponding to the measured object in the initial state and the final state, and the result of the corresponding parameter of the measured object is obtained according to the difference;

[0017] The change of the initial state and final state of the measured object on the interference generating device is limited to the change of the optical path difference brought about by replacing the adjuster.

[0018] The present invention has the following beneficial effects:

[0019] 1. Through the optical path difference, the positioning can be accurately achieved at the nanometer level. The changes in the initial state and final state of the object under test that affect the interference generating device replace the changes in the optical path difference caused by the regulator. Then, the reference curve is searched to obtain the difference between the optical path differences corresponding to the initial state and the final state of the object under test. Finally, the corresponding parameters of the object under test are obtained based on the difference. The whole process is simple, convenient and highly accurate.

[0020] 2. In the process of calculating the speckle contrast, the threshold range of the light intensity corresponding to the intercepted circular ring area and the corresponding inner and outer ring pixel radius are determined according to the maximum value of the grayscale value, and the region interception and calculation standard of the speckle contrast in the series of speckle images are unified through automatic image recognition, ensuring the high precision and high reliability of the reference curve. In the subsequent process of replacing the change of the optical path difference caused by the regulator with the change of the interference generating device caused by the initial state and the final state of the measured object, the region interception and speckle contrast calculation are also based on the unified standard, thereby further ensuring that the logic of obtaining the difference between the optical path differences corresponding to the initial state and the final state of the measured object by table comparison is rigorous and reliable.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0023] Figure 1 It is a system block diagram of measuring the positioning accuracy of a linear translation stage based on a single longitudinal mode laser according to an embodiment of the present invention.

[0024] Figure 2 It is a partially enlarged schematic diagram of a part of the speckle area disclosed in an embodiment of the present invention.

[0025] Figure 3 It is a schematic diagram of gray value curves at different pixel radii in a single-frame speckle image disclosed in an embodiment of the present invention.

[0026] Figure 4 It is a schematic diagram of the coordinate mapping relationship of mapping a circular area to a square area disclosed in an embodiment of the present invention.

[0027] Figure 5 It is a schematic diagram of the wavelength distribution curve of the single longitudinal mode laser disclosed in the embodiment of the present invention, wherein the horizontal axis is the wavelength and the vertical axis is the intensity value of the spectrum normalization.

[0028] Figure 6 It is a schematic diagram of the regular distribution between speckle contrast and optical path difference disclosed in an embodiment of the present invention.

[0029] Figure 7 It is a schematic diagram of specific components of a system for measuring parameters of a measured object based on single longitudinal mode laser disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0031] Example 1

[0032] This embodiment discloses a system for measuring parameters of an object under test based on a single longitudinal mode laser. Figure 1 As shown, including:

[0033] The interference generating device whose light source is a single longitudinal mode laser, and a regulator for changing the optical path is arranged in a beam of light waves that generate interference. In this embodiment, the interference generating device can be any interferometer that can generate annular interference fringes.

[0034] A scattering sheet presenting the interference image generated by the interference generating device.

[0035] An image collector is used to take a picture of the pattern presented by the scattering sheet. The characteristics of the part of the speckle captured by the image collector are as follows: Figure 2 As shown, the image on the right is a schematic diagram of the local enlarged structure of the rectangular area on the left.

[0036] The system of this embodiment further includes a host for data communication with the image collector, and is used to obtain from the image collector a series of speckle images collected by the adjuster in the process of changing the optical path, calculate the gray value curves under different pixel radii in each frame of the speckle image, determine the threshold range of the light intensity corresponding to the intercepted circular area according to the maximum gray value, and then determine the pixel radius sizes corresponding to the inner and outer rings of the circular area according to the threshold range; then calculate the speckle contrast of the intercepted circular area in each frame of the speckle image, calibrate at least three discrete data of the speckle contrast weakening as the optical path difference increases, and fit the discrete data according to each of the discrete data. A reference curve is obtained in which the speckle contrast decreases as the optical path difference increases within a measurement range, and the maximum value of the measurement range is less than or equal to the single longitudinal mode laser coherence length; then a speckle picture corresponding to a final state of the measured object after being placed in the interference beam is obtained from the image collector, the speckle contrast of the final state obtained by calculation is compared with the speckle contrast corresponding to an initial state of the measured object before being placed in the interference beam or after being placed in the interference beam, the reference curve is searched to obtain the difference between the optical path differences corresponding to the measured object in the initial state and the final state, and a result of the corresponding parameter of the measured object is obtained according to the difference.

[0037] The change of the initial state and final state of the measured object on the interference generating device is limited to the change of the optical path difference brought about by replacing the adjuster.

[0038] Specifically, in this embodiment, a region is selected on each frame of the speckle image to calculate the speckle contrast. The region can be selected by drawing gray value curves under different pixel radii. Figure 3 As shown in FIG. 1 , a preferred gray value curve is specifically as follows: the horizontal axis is the pixel radius of the pixel point, and the vertical axis is the gray value intensity. After finding the first maximum intensity point Imax, a threshold is taken. Preferably, the threshold = Imax*86.5%, as shown in FIG. Figure 3 As shown, the selected area is the pixel point range corresponding to the threshold. As a prerequisite, before calculating the gray value intensity of each pixel radius, the circular boundary between multiple light and dark ring stripes is first identified through the image to roughly calculate multiple potential center coordinates, and then the average value of the multiple potential center coordinates is taken to accurately locate the center coordinates. Afterwards, in the process of calculating the speckle contrast, the pixel information of the intercepted circular ring area is first converted into the pixel information of the rectangular area through polar coordinate transformation and interpolation algorithm, and then the speckle contrast corresponding to the rectangular area is calculated, and the calculation result of the speckle contrast corresponding to the rectangular area is equal to the speckle contrast result of the intercepted circular ring area. Specifically: The calculation formula of speckle contrast C is:

[0039] C=Std(I) / Mean(I)

[0040] Among them, I is the gray value intensity, Std(I) represents the standard deviation of the intensity on the image, and Mean(I) represents the average value of the intensity on the image.

[0041] Reference Figure 3 , the pixel information of the circular area is transformed into the pixel information of the rectangular area through polar coordinate transformation and interpolation algorithm, specifically including:

[0042] 1. In a two-dimensional coordinate system, the (x, y) value is used to describe the position of a point, while in a polar coordinate system, the distance ρ to the origin and the angle θ are used to describe the position of the point.

[0043] 2. First of all, normal images are in a rectangular coordinate system and can be regarded as a two-dimensional plane. If we want to transform the image coordinates, we must first convert the position to a new coordinate system and then assign the value to it. Here we need to determine the position and grayscale value, that is, the grayscale value and position of any pixel after the transformation, and the grayscale value after the transformation remains unchanged.

[0044] 3. Solve the positional relationship of the transformation. The key to polar coordinate transformation and its inverse transformation is to determine the pixel value of each pixel on the image after polar coordinate transformation based on the image before polar coordinate transformation. That is, find Figure 3 The correspondence between the geometric coordinates of the "circle diagram" on the left and the "square diagram" on the right.

[0045] like Figure 4 As shown, the key to realize polar coordinate transformation is to find the corresponding point p(m, n) on the square graph for any point P(i, j) on the circular graph, for example, P(0, 10), R=10, and then realize the assignment of all pixel points on the circular graph through interpolation algorithm.

[0046] On the square diagram, the number of rows and columns is M and N respectively. Each column on the square diagram corresponds to each radius on the circular diagram. There is a length scaling factor delta_r = M / R in the radial direction. If M is 10, then delta_r = 1. The circumference is divided into N equal parts, that is, the angle factor is delta_t = 2π / N. If N is 32, then delta_t = 2π / 32 = π / 16.

[0047] On the circular graph, the image coordinates (i, j) and the world coordinates (x, y) have the following transformation relationship: x = j-R, y = R-i; then the world coordinates corresponding to P (0, 10) are temporarily taken as (0, 10). Then, the radius length of point P in the figure is r = sqrt (xx + yy) = 10, and the angle theta = arctan (y / x) = π / 2; thus, the number of rows corresponding to point P on the circular graph on the square graph is r / delta_r = 10 / 1 = 10; the number of columns corresponding to point P on the circular graph on the square graph is n = thata / delta_t = 8. The above is the basic principle of polar coordinate transformation. Combined with the corresponding interpolation algorithm, the polar coordinate transformation of the image can be realized.

[0048] In this embodiment, the wavelength λ of the laser and the longitudinal mode wavelength interval △λ are known, and the coherence length Lc of the laser can be calculated in advance:

[0049] L c =λ 2 / △λ

[0050] Where △λ is the half-maximum full width of the single longitudinal mode laser spectrum. Figure 5 The single longitudinal mode laser shown in the figure, then the spot contrast obtained based on the single longitudinal mode laser changes with the optical path difference as shown in the figure. Figure 6 As shown, this is the distribution law of the benchmark curve.

[0051] Optionally, in a specific application scenario, the object to be measured is a displacement stage, and the displacement stage is provided with a first, a second, a third and a fourth reflector, the first reflector reflects the incident light beam to the second reflector, the second reflector reflects the incident light beam to the third reflector, and the third reflector reflects the incident light beam to the fourth reflector; wherein the normals of the first, the second, the third and the fourth reflectors each form an angle of 45 degrees with the incident light beam, and the second reflector and the third reflector are synchronously displaced in a straight line with equal intervals between the first reflector and the fourth reflector respectively under manual or electric drive; the initial state is the initial state of the displacement stage after being placed in the interference light beam, and the corresponding parameter of the object to be measured is the positioning accuracy calculated by comparing the optical path difference actually measured according to the spot contrast with the travel between the initial state and the final state obtained by the displacement stage itself.

[0052] Alternatively, if Figure 7 As shown, a system for measuring the parameters of the object under test based on a single longitudinal mode laser specifically includes: the light emitted by the longitudinal mode laser passes through the first polarizer 10 and the first half-wave plate (for rotating the polarization direction of the laser) 20 in sequence, and is then split into P light and S light by the first PBS (the transmitted light is P light, and the reflected light is S light), and then the P light passes through the displacement stage 40 and the fifth reflector 60 in sequence to reach the second PBS, and the S light also reaches the second PBS after being reflected by the sixth reflector 50, and the two beams of light combined in the second PBS produce interference, and are imaged on the scattering plate 90 after the polarization direction is selected by the second polarizer 80, and then the fixed focus lens 100 of the image collector realizes the acquisition of the speckle image. Among them, the first reflector 41, the second reflector 43, the third reflector 44 and the fourth reflector 42 as described above are arranged on the displacement stage 40; and during the test process, the positions of the first and fourth reflectors 41 and 42 are fixed, and the second and third reflectors 43 and 44 can be synchronously displaced with the first and fourth reflectors 41 and 42 in the direction of travel as shown by the dotted line in the figure. Based on this system, the optical path difference generated by the displacement stage is twice the linear displacement of the displacement stage. Thus, assuming that the actual optical path difference obtained by the interference fringe speckle contrast is 10 nanometers, the corresponding actual displacement of the linear displacement stage is 5 nanometers. If the data formed by the displacement stage itself is 4.8 nanometers, the positioning accuracy error is 4%. Among them, the nanometer-level positioning in this embodiment mainly depends on the accuracy of calibration. For this reason, when calibrating, it is preferred to use a piezoelectric displacement stage to achieve nanometer-level calibration. It is worth noting that in this method, the displacement stage can be the above-mentioned "regulator" itself.

[0053] In another application scenario, the object to be measured in this embodiment may be glass, and the corresponding parameter of the object to be measured is the refractive index or glass thickness of the glass (usually the thickness is measured with a known refractive index, or the refractive index is measured with a known thickness), and the initial state is the state where it is not placed in front of the corresponding interference beam. Optionally, the glass can replace the above-mentioned regulator, and the speckle contrast after the glass is placed in the interference beam is compared with the speckle contrast before the interference beam, and the optical path difference before and after the operation is obtained by looking up the table, and then subsequent calculations are performed. As a variation, if the initial regulator of the system adopts the above-mentioned displacement stage with the first, second, third and fourth reflectors; the measured glass can also be placed between the first and second reflectors, between the second and third reflectors, or between the third and fourth reflectors, and the replacement operation can be omitted. However, unlike the above-mentioned linear displacement, when the measured glass is placed between two adjacent reflectors, the overall optical path difference generated is equal to the optical path difference generated by a single measured glass, rather than the above-mentioned 2-fold relationship.

[0054] Example 2

[0055] Corresponding to the above embodiment, this embodiment discloses a method for measuring parameters of a measured object based on a single longitudinal mode laser, comprising:

[0056] Step S1, deploying a system for measuring parameters of an object to be measured based on single longitudinal mode laser.

[0057] The system is the same as that shown in Example 1 Figure 1 , comprising: an interference generating device whose light source is a single longitudinal mode laser, an adjuster for changing the optical path in a beam of light waves generating interference, a scattering sheet for presenting the interference image generated by the interference generating device, an image collector for photographing the pattern presented by the scattering sheet, and a host for data communication with the image collector. The method comprises:

[0058] Step S2, the host obtains from the image collector a series of speckle images collected by the adjuster in the process of changing the optical path, calculates the gray value curves under different pixel radii in each frame of the speckle image, determines the threshold range of the light intensity corresponding to the intercepted circular area according to the maximum gray value, and then determines the pixel radius sizes corresponding to the inner and outer rings of the circular area according to the threshold range; then calculates the speckle contrast of the intercepted circular area in each frame of the speckle image, and calibrates at least three discrete data of the speckle contrast weakening as the optical path difference increases, and fits the speckle contrast within the measurement range according to each discrete data. A reference curve whose contrast decreases as the optical path difference increases, and the maximum value of the measurement range is less than or equal to the single longitudinal mode laser coherence length; then a speckle picture corresponding to the final state of the measured object after being placed in the interference beam is obtained from the image collector, the speckle contrast of the final state obtained by calculation is compared with the speckle contrast corresponding to the initial state of the measured object before being placed in the interference beam or after being placed in the interference beam, the reference curve is searched to obtain the difference between the optical path differences corresponding to the initial state and the final state of the measured object, and the result of the corresponding parameter of the measured object is obtained according to the difference.

[0059] The change of the initial state and final state of the measured object on the interference generating device is limited to the change of the optical path difference brought about by replacing the adjuster.

[0060] Preferably, as in the above-mentioned embodiment 1, the method of this embodiment further comprises: in the process of calculating the speckle contrast, firstly transforming the pixel information of the intercepted circular area into the pixel information of the rectangular area through polar coordinate transformation and interpolation algorithm, and then calculating the speckle contrast corresponding to the rectangular area, and making the calculation result of the speckle contrast corresponding to the rectangular area equal to the speckle contrast result of the intercepted circular area.

[0061] Similarly, the object to be measured in this embodiment may be glass, the corresponding parameter of the object to be measured is the refractive index or glass thickness of the glass, and the initial state is a state where it is not placed in front of the corresponding interference light beam.

[0062] Similarly, the object to be measured described in this embodiment can be a displacement stage, and the displacement stage is provided with a first, a second, a third and a fourth reflector, the first reflector reflects the incident light beam to the second reflector, the second reflector reflects the incident light beam to the third reflector, and the third reflector reflects the incident light beam to the fourth reflector; wherein the normals of the first, the second, the third and the fourth reflectors are respectively at an angle of 45 degrees to the incident light beam, and the second reflector and the third reflector are synchronously displaced in a straight line with equal spacing between the first reflector and the fourth reflector under manual or electric drive; the initial state is the initial state of the displacement stage after being placed in the interference light beam, and the corresponding parameter of the object to be measured is the positioning accuracy calculated by comparing the optical path difference actually measured according to the spot contrast with the travel distance between the initial state and the final state obtained by the displacement stage itself.

[0063] In summary, the system and method for measuring parameters of an object under test based on single longitudinal mode laser disclosed in the embodiments of the present invention have the following beneficial effects:

[0064] 1. Through the optical path difference, the positioning can be accurately achieved at the nanometer level. The changes in the initial state and final state of the object under test that affect the interference generating device replace the changes in the optical path difference caused by the regulator. Then, the reference curve is searched to obtain the difference between the optical path differences corresponding to the initial state and the final state of the object under test. Finally, the corresponding parameters of the object under test are obtained based on the difference. The whole process is simple, convenient and highly accurate.

[0065] 2. In the process of calculating the speckle contrast, the threshold range of the light intensity corresponding to the intercepted circular ring area and the corresponding inner and outer ring pixel radius are determined according to the maximum value of the grayscale value, and the region interception and calculation standard of the speckle contrast in the series of speckle images are unified through automatic image recognition, ensuring the high precision and high reliability of the reference curve. In the subsequent process of replacing the change of the optical path difference caused by the regulator with the change of the interference generating device caused by the initial state and the final state of the measured object, the region interception and speckle contrast calculation are also based on the unified standard, thereby further ensuring that the logic of obtaining the difference between the optical path differences corresponding to the initial state and the final state of the measured object by table comparison is rigorous and reliable.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for measuring parameters of an object based on single longitudinal mode laser, characterized in that: include: The light source is an interference generating device of a single longitudinal mode laser, and a regulator for changing the optical path is arranged in a beam of light waves generating interference; A scattering sheet presenting the interference image generated by the interference generating device; An image collector for taking a picture of the pattern presented by the scattering sheet; A host computer that performs data communication with the image collector is used to obtain from the image collector a series of speckle images collected by the adjuster in the process of changing the optical path, calculate the gray value curves under different pixel radii in each frame of the speckle image, determine the threshold range of the light intensity corresponding to the intercepted circular ring area according to the maximum gray value, and then determine the pixel radius sizes corresponding to the inner and outer rings of the circular ring area according to the threshold range; then calculate the speckle contrast of the intercepted circular ring area in each frame of the speckle image, calibrate at least three discrete data of the speckle contrast weakening as the optical path difference increases, and fit the speckle contrast within the measurement range according to each discrete data. A reference curve is obtained in which the speckle contrast in a range decreases as the optical path difference increases, and the maximum value of the measurement range is less than or equal to the coherence length of the single longitudinal mode laser; then a speckle picture corresponding to the final state of the measured object after being placed in the interference beam is obtained from the image collector, and the calculated speckle contrast of the final state is compared with the speckle contrast corresponding to the initial state of the measured object before being placed in the interference beam or after being placed in the interference beam, and the reference curve is searched to obtain the difference between the optical path differences corresponding to the initial state and the final state of the measured object, and the result of the corresponding parameter of the measured object is obtained according to the difference; The change of the initial state and final state of the measured object on the interference generating device is limited to the change of the optical path difference brought about by replacing the adjuster.

2. The system according to claim 1, characterized in that Also includes: In the process of speckle contrast calculation, the pixel information of the intercepted circular area is first converted into the pixel information of the rectangular area through polar coordinate transformation and interpolation algorithm, and then the speckle contrast corresponding to the rectangular area is calculated, and the calculation result of the speckle contrast corresponding to the rectangular area is equal to the speckle contrast result of the intercepted circular area.

3. The system according to claim 1 or 2, characterized in that: The measured object is glass, the corresponding parameter of the measured object is the refractive index or glass thickness of the glass, and the initial state is a state where the object is not placed in front of the corresponding interference light beam.

4. The system according to claim 1 or 2, characterized in that: The object to be measured is a displacement stage, and the displacement stage is provided with a first, a second, a third and a fourth reflector, the first reflector reflects the incident light beam to the second reflector, the second reflector reflects the incident light beam to the third reflector, and the third reflector reflects the incident light beam to the fourth reflector; wherein the normals of the first, the second, the third and the fourth reflectors are each at an angle of 45 degrees to the incident light beam, and the second reflector and the third reflector are synchronously displaced in a straight line with equal spacing between the first reflector and the fourth reflector under manual or electric drive; the initial state is the initial state of the displacement stage after being placed in the interference light beam, and the corresponding parameter of the object to be measured is the positioning accuracy calculated by comparing the optical path difference actually measured according to the spot contrast with the travel between the initial state and the final state obtained by the displacement stage itself.

5. A method for measuring parameters of an object under test based on single longitudinal mode laser, characterized in that: include: Step S1: deploying a system for measuring parameters of an object to be measured based on a single longitudinal mode laser, the system comprising: The light source is an interference generating device of a single longitudinal mode laser, and a regulator for changing the optical path is arranged in a beam of light waves generating interference; A scattering sheet presenting the interference image generated by the interference generating device; An image collector for taking a picture of the pattern presented by the scattering sheet; A host computer that performs data communication with the image collector, the method comprising: The host obtains a series of speckle images collected by the regulator in the process of changing the optical path from the image collector, calculates the gray value curves under different pixel radii in each frame of the speckle image, determines the threshold range of the light intensity corresponding to the intercepted circular area according to the maximum gray value, and then determines the pixel radius sizes corresponding to the inner and outer rings of the circular area according to the threshold range; then calculates the speckle contrast of the intercepted circular area in each frame of the speckle image, and calibrates at least three discrete data of the speckle contrast weakening as the optical path difference increases, and fits the speckle contrast within the measurement range according to each discrete data. A reference curve is obtained in which the optical path difference is increased and weakened, and the maximum value of the measurement range is less than or equal to the coherence length of the single longitudinal mode laser; then a speckle picture corresponding to the final state of the measured object after being placed in the interference beam is obtained from the image collector, and the speckle contrast of the final state obtained by calculation is compared with the speckle contrast corresponding to the initial state of the measured object before being placed in the interference beam or after being placed in the interference beam, and the reference curve is searched to obtain the difference between the optical path differences corresponding to the measured object in the initial state and the final state, and the result of the corresponding parameter of the measured object is obtained according to the difference; The change of the initial state and final state of the measured object on the interference generating device is limited to the change of the optical path difference brought about by replacing the adjuster.

6. The method according to claim 5, characterized in that Also includes: In the process of speckle contrast calculation, the pixel information of the intercepted circular area is first converted into the pixel information of the rectangular area through polar coordinate transformation and interpolation algorithm, and then the speckle contrast corresponding to the rectangular area is calculated, and the calculation result of the speckle contrast corresponding to the rectangular area is equal to the speckle contrast result of the intercepted circular area.

7. The method according to claim 5 or 6, characterized in that: The measured object is glass, the corresponding parameter of the measured object is the refractive index or glass thickness of the glass, and the initial state is a state where the object is not placed in front of the corresponding interference light beam.

8. The method according to claim 5 or 6, characterized in that: The object to be measured is a displacement stage, and the displacement stage is provided with a first, a second, a third and a fourth reflector, the first reflector reflects the incident light beam to the second reflector, the second reflector reflects the incident light beam to the third reflector, and the third reflector reflects the incident light beam to the fourth reflector; wherein the normals of the first, the second, the third and the fourth reflectors are each at an angle of 45 degrees to the incident light beam, and the second reflector and the third reflector are synchronously displaced in a straight line with equal spacing between the first reflector and the fourth reflector under manual or electric drive; the initial state is the initial state of the displacement stage after being placed in the interference light beam, and the corresponding parameter of the object to be measured is the positioning accuracy calculated by comparing the optical path difference actually measured according to the spot contrast with the travel between the initial state and the final state obtained by the displacement stage itself.

Images