Speckle interferometry system and method

Abstract

The present application provides a kind of speckle interferometry system and method, it is related to a kind of optical measurement system, including parallel light generating device, for generating parallel light;Part of the parallel light is reflected by mirror one and is irradiated on spectroscope one, is divided into reflected light one and transmission light by spectroscope one;Part of the reflected light one is irradiated on the diffused reflection of measured surface, forms reflected light two;Part reflected light two successively passes through spectroscope one, Fourier lens one, diaphragm, Fourier lens two and spectroscope two, as object light is irradiated on the camera imaging surface;Part transmission light is reflected by mirror two, mirror three and spectroscope two in turn, as reference light is irradiated on the camera imaging surface;The system provided by the present application helps to solve the problem of decorrelation effect caused by large in-plane deformation in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical measurement system, in particular to a speckle interferometry system and method. BACKGROUND

[0002] Laser irradiation occurs diffuse reflection on the rough surface of the object, and speckle is generated by random interference on the image plane. Speckle interference obtains the fringe pattern corresponding to the object deformation information by measuring the superposition of speckle pattern complex amplitude. The contrast of the fringe depends on the correlation of the speckle field. When the environment is disturbed and the object vibrates, out-of-plane and in-plane displacements are generated, and the relative position of the speckle field changes. When the relative position change exceeds the correlation distance of the speckle field, the decorrelation effect is caused. For the decorrelation caused by the out-of-plane displacement, the aperture stop can be reduced to increase the correlation distance in the axial direction of the speckle. However, the in-plane correlation distance of the speckle is relatively short, and at the same time, the in-plane deformation often has a large amplitude, which is easy to exceed the transverse correlation distance of the speckle, so that the speckle fields before and after deformation are completely unrelated, and speckle interferometry cannot be performed.

[0003] Therefore, how to solve the decorrelation effect caused by the large in-plane deformation is an urgent problem to be solved. SUMMARY

[0004] (I) Technical problems solved

[0005] In view of the deficiencies in the prior art, the present application provides a speckle interferometry system and method to solve the technical problem of decorrelation effect caused by large in-plane deformation in the prior art.

[0006] (II) Technical solutions

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

[0008] The present application provides a speckle interferometry system, comprising a parallel light generating device for generating parallel light;

[0009] Part of the parallel light is reflected by a mirror one and irradiated on a beam splitter prism one, and is divided into reflected light one and transmitted light by the beam splitter prism one;

[0010] Part of the reflected light one is irradiated on the measured surface to form reflected light two by diffuse reflection;

[0011] Part of the reflected light two passes through the beam splitter prism one, the Fourier lens one, the aperture stop, the Fourier lens two and the beam splitter prism two in sequence, and is irradiated on the camera imaging surface as object light;

[0012] Part of the transmitted light is reflected by a mirror two, a mirror three and a beam splitter prism two in sequence, and is irradiated on the camera imaging surface as reference light;

[0013] Wherein, Fourier lens one and Fourier lens two constitute a 4f system, the measured surface is on the front focal plane of Fourier lens one, the camera imaging plane is on the back focal plane of Fourier lens two, and the diaphragm is on the spectral plane of the 4f system.

[0014] Further, the diaphragm is an aperture diaphragm with adjustable aperture.

[0015] Further, the mirror two is connected with a driving structure one for adjusting the reflection angle thereof.

[0016] Further, the mirror three is connected with a driving structure two for adjusting the reflection angle thereof.

[0017] Further, the parallel light generating device comprises a laser and a collimating and expanding mirror, and the laser generates laser light which is expanded by the collimating and expanding mirror and then irradiated on the beam splitter prism one as parallel light.

[0018] The second aspect of the present application also provides a method for speckle interferometry by using the above system, the method comprising:

[0019] Obtaining two pairs of speckle interferograms of the measured surface before and after deformation in the same coordinate system;

[0020] Obtaining the amplitude correlation coefficient μ corresponding to the selected block for each element in the search set amc , and <> is statistical average, and * is conjugate operation;

[0021] (x, y) is the coordinate of a point in a two-dimensional coordinate system on the camera imaging plane 8, and the origin of the two-dimensional coordinate system is the intersection of the optical axis and the camera imaging plane 8 in the 4f system;

[0022] O(x, y) is the complex amplitude of the object light in the selected block, O shift (x, y) is the complex amplitude of the object light in the traversal block; wherein the selected block is obtained by the search frame in the speckle interferogram before deformation of the measured surface, the traversal block is obtained by the search frame in the speckle interferogram after deformation of the measured surface according to the set traversal rule, and all the traversal blocks obtained by the search frame in the speckle interferogram after deformation of the measured surface according to the set traversal rule form the search set;

[0023] Then, the traversal block corresponding to the maximum value of all the amplitude correlation coefficients is obtained, and is taken as the offset block;

[0024] Obtaining the corrected interferogram after the interference pattern corresponding to the traversal block is offset, and the center coordinates of the offset block in the corrected interferogram are the same as the center coordinates of the selected block;

[0025] Calculating the out-of-plane deformation of the measured surface by using the corrected interferogram and the interference pattern corresponding to the selected block.

[0026] Further, the center coordinates of the selected block coincide with the origin of the two-dimensional coordinate system.

[0027] Further, the speckle interference pattern corresponding to the selected block is the speckle interference pattern obtained before deformation of the measured surface.

[0028] (III) Beneficial effects

[0029] The speckle interferometry system and method provided by the application have the following beneficial effects compared with the prior art:

[0030] 1. The illumination light is parallel light, and the imaging light path is a telecentric light path in the object side, so as to avoid internal changes in the speckle field caused by angle conversion of the illumination light when the object undergoes in-plane vibration.

[0031] 2. The spatial carrier wave technology is used to extract the complex amplitude of the object light field from a single speckle interference pattern, so as to meet the needs of dynamic measurement scenarios.

[0032] 3. The amplitude correlation coefficient is proposed, so as to effectively calculate the correlation of the speckle fields before and after deformation, and thus to determine the distance of in-plane displacement caused by vibration.

[0033] 4. The amplitude correlation coefficient of the object light field before and after deformation is used to calculate the displacement, and after correction, the phase difference between the speckle fields before and after deformation is subtracted, so as to obtain a high-quality fringe pattern, thereby improving the deformation measurement precision. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0035] Figure 1 Fig. 1 shows a schematic diagram of the light path structure of a speckle interferometry system provided by embodiment 1;

[0036] In the figure:

[0037] 1. Parallel light generating device; 2. Mirror 1; 3. Splitting prism 1; 4. Fourier lens 1; 5. Diaphragm; 6. Fourier lens 2; 7. Splitting prism 2; 8. Camera imaging surface; 9. Mirror 2; 10. Mirror 3. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] Combined with attachment Figure 1 This embodiment provides a speckle interferometry measurement system, including a parallel light generating device 1 for generating parallel light. In some embodiments, the parallel light generating device 1 includes a laser and a collimating beam expander, and the laser light generated by the laser is expanded by the collimating beam expander and then irradiated onto a beam splitter prism 3 as parallel light to obtain the parallel light.

[0041] The parallel light generated by the parallel light generating device 1 is first irradiated on the reflector 2, wherein part (or all) of the parallel light is reflected by the reflector 2 and then irradiated on the dichroic prism 3, and is divided into reflected light 1 and transmitted light by the dichroic prism 3; wherein, the reflector 2 is used to reflect the parallel light on the dichroic prism 3, and the reflection angle of the reflector 2 is adjustable. In some embodiments, it is connected to the driving structure 3 to adjust the reflection angle of the parallel light as needed.

[0042] A portion (or all) of the reflected light 1 reflected by the dichroic prism 13 is irradiated on the measured surface and is diffusely reflected to form reflected light 2.

[0043] Part (or all) of the reflected light 2 passes through the beam splitter prism 1 3, the Fourier lens 1 4, the aperture 5, the Fourier lens 2 6 and the beam splitter prism 2 7 in sequence, and then illuminates the camera imaging surface 8 as object light;

[0044] Part (or all) of the transmitted light from the parallel light passing through the beam splitter prism 1 3 is reflected in sequence by the reflector 2 9, the reflector 3 10 and the beam splitter prism 2 7, and then irradiates the camera imaging surface 8 as reference light.

[0045] Among them, Fourier lens 1 4 and Fourier lens 2 6 form a 4f system, and the measured surface is on the front focal plane of Fourier lens 1 4, the camera imaging surface 8 is on the back focal plane of Fourier lens 2 6, and the aperture 5 is on the spectrum plane of the 4f system.

[0046] In order to facilitate the adjustment of the size of the speckle particles, in this embodiment, the diaphragm 5 is an aperture diaphragm with an adjustable aperture.

[0047] In order to facilitate the adjustment of the reflection angles of the mirror two 9 and the mirror three 10, in the embodiment, the mirror two 9 is connected with a driving structure one for adjusting the reflection angle thereof, and the mirror three 10 is connected with a driving structure two for adjusting the reflection angle thereof.

[0048] That is, the mirror two 9 and the mirror three 10 can be respectively adjusted by the driving structure one and the driving structure two.

[0049] In the actual adjustment process, in the embodiment, the mirror two 9 is used to adjust the incident angle of the reference light, and the mirror three 10 is used to adjust the spot position of the reference light, so as to ensure that the reference light and the object light spot are overlapped, and the carrier frequency introduced by the reference light is adjusted in the case of maximizing the interference area.

[0050] Reference Figure 1 The speckle interferometry measurement system provided in the embodiment constitutes a measurement system of parallel light illumination and telecentric imaging light path, wherein, before the deformation of the measured surface, the object light wave U o (x, y) and the reference light wave U r respectively have:

[0051]

[0052] Wherein, A o(x,y) , A r , are respectively the object light amplitude, the object light phase, the reference light amplitude and the reference light phase in the speckle interference pattern obtained on the camera imaging surface 8 before the deformation of the measured surface, i is an imaginary unit, 2πf x x is the carrier introduced in the x direction by the reference light in the speckle interference pattern obtained on the camera imaging surface 8, f x is the frequency of the introduced carrier.

[0053] In the embodiment, since the reference light is set as a plane wave, its amplitude and phase are constant and are constants (i.e. A r , and 2πf x are constants before and after the deformation of the measured surface), which are not affected by the deformation of the measured surface, so as to simplify the derivation process, in the embodiment, it is set that the reference light only introduces the carrier in the x direction.

[0054] Wherein, before the deformation of the measured surface and before the reference light introduces the carrier, the speckle interference pattern I(x, y) obtained on the camera imaging surface 8 has:

[0055]

[0056] Then it is obvious that after the reference light introduces the carrier, the above formula becomes:

[0057] where k c = 2πf x .

[0058] Then when the measured surface occurs out-of-plane deformation, the resulting speckle interferogram I ′ (x,y) on the camera imaging plane 8 has:

[0059]

[0060] φ out (x,y) is the phase introduced when the measured surface occurs out-of-plane deformation, then when the measured surface occurs out-of-plane deformation at the same time causes in-plane deformation, the corresponding speckle interferogram I shift (x,y) has:

[0061]

[0062] u and v are the deformation amounts of the measured surface in-plane deformation in the x-axis and y-axis directions, respectively.

[0063] Fourier transform is performed on the speckle interferograms obtained before and after deformation, a bandpass filter is designed according to the size of the system aperture diaphragm and the size of the introduced carrier frequency, the high-frequency part containing the object light information is extracted through the bandpass filter, and the object light complex amplitude O(x,y) before deformation of the measured surface and the object light complex amplitude O shift (x,y) after deformation of the measured surface are obtained by inverse Fourier transform.

[0064] O(x,y) = IFFT(FFT(I) * BandpassFilter);

[0065] O shift (x,y) = IFFT(FFT(I shift ) * BandpassFilter);

[0066] BandpassFilter is a bandpass filter manually selected according to the carrier frequency.

[0067] In-plane vibration will cause the object light complex amplitude to be misaligned as a whole, so that the speckle fields in the speckle interferograms obtained before and after deformation are no longer consistent, and the decorrelation phenomenon occurs. The quantitative judgment of the degree of decorrelation is the key to correction. Therefore, a correlation coefficient type evaluation index is introduced to measure the consistency between the complex amplitude fields before and after deformation, to evaluate the image misalignment caused by in-plane deformation, and to provide a quantitative basis for subsequent image matching and displacement compensation. Generally, the correlation of the complex amplitude is measured by calculating the complex correlation coefficient μ, which is defined as follows:

[0068]

[0069] where < > is statistical average, and * is conjugate operation.

[0070] It can be found that if the complex correlation coefficient is directly calculated, the complex correlation coefficient will be disturbed by the phase difference, which is caused by the translation of the initial random speckle field before and after deformation and the out-of-plane deformation of the object. However, the amplitude of the object light complex amplitude will not be affected by the phase, but will be modulated by the in-plane translation of the object light, so the conjugate multiplication of the molecule is firstly modulated and then averaged, that is, the amplitude correlation of the complex amplitudes of the object light before and after deformation is calculated, so as to avoid the influence of the phase and obtain the accurate correlation coefficient, so the amplitude correlation coefficient μ amc is proposed in the embodiment.

[0071]

[0072] After extracting the object light complex amplitude of the speckle patterns before and after deformation, the amplitude correlation coefficient is introduced as the matching criterion in the search algorithm. The coefficient measures the correspondence between the selected complex amplitude modulus (i.e. amplitude) in the two regions of the same size in the speckle interference patterns obtained before and after deformation of the measured object, and essentially acts as a "target function" or "similarity evaluation index" in the search process.

[0073] Compared with the traditional complex correlation coefficient, the amplitude correlation coefficient is not disturbed by the phase difference and can more stably reflect the speckle translation caused by in-plane deformation. When the traversal block under different offsets in the search area is traversed, the amplitude correlation coefficient is used as an optimization criterion to evaluate the matching degree of each pair of regions, and finally the offset that makes the amplitude correlation coefficient maximum is selected as the optimal correspondence between images, so as to realize effective correction of the speckle decorrelation.

[0074] That is, when performing speckle interferometry by using the above-mentioned speckle interferometry system, the following method is performed, and the method specifically includes:

[0075] Obtaining two pairs of speckle interference patterns obtained before and after deformation of the measured surface in the same coordinate system;

[0076] Obtaining the amplitude correlation coefficient μ amc of each element in the search set corresponding to the selected block, and < > is statistical average, and * is conjugate operation.

[0077] (x, y) is the coordinate of a point in the two-dimensional coordinate system on the camera imaging surface 8, and the origin of the two-dimensional coordinate system is the intersection of the optical axis and the camera imaging surface 8 in the 4f system;

[0078] O(x, y) is the object light complex amplitude in the selected block, and O shift(x, y) is the complex amplitude of the object light in the traversal block;

[0079] wherein the selected block is framed by the search frame in one speckle interferogram, the traversal block is framed by the search frame in another speckle interferogram according to the set traversal rule, and the search frame frames all the traversal blocks in the corresponding speckle interferogram according to the set traversal rule to form a search set;

[0080] Then the traversal block corresponding to the maximum value of all the amplitude correlation coefficients is obtained as the offset block.

[0081] The corrected interferogram obtained after the offset of the traversal block is obtained, and the center coordinates of the offset block in the corrected interferogram are the same as the center coordinates of the selected block.

[0082] The out-of-plane deformation of the measured surface is calculated by using the corrected interferogram and the interferogram corresponding to the selected block.

[0083] That is, by comparing the center coordinates of the offset block with the center coordinates of the selected block, the offset amount of the speckle interferogram corresponding to the offset block relative to the speckle interferogram corresponding to the selected block (the offset amount is the difference between the center coordinates of the offset block and the center coordinates of the selected block) can be obtained. Then, according to the offset amount, the speckle interferogram corresponding to the offset block is offset by the offset amount, so that the center coordinates of the offset block in the corrected interferogram are the same as the center coordinates of the selected block in the speckle interferogram corresponding to the selected block (without offset). Then, the out-of-plane deformation of the measured surface can be calculated by using the corrected interferogram and the interferogram corresponding to the selected block.

[0084] In the embodiment, the set traversal rule is specifically that the search frame starts searching from a corner (such as the lower left corner) of the obtained speckle interferogram. Figure 1 For example, in the embodiment, the search frame is a rectangular frame, which is initially located at a corner of the speckle interferogram and one corner of the search frame coincides with one corner of the speckle interferogram, and the search frame is located in the speckle interferogram. Then, the framed block is taken as a traversal block, and the amplitude correlation coefficient of the selected block is calculated. Meanwhile, the selected block is taken as an element in the search set. During the traversal, the search frame is moved by 1 pixel distance to one side of the speckle interferogram, and a new traversal block is obtained after the movement. When the search frame moves to a corner (such as the lower right corner) and coincides with a corner of the speckle interferogram, the search frame is moved by 1 pixel distance upwards to obtain a new traversal block. Then, the search frame is gradually moved to the left by 1 pixel distance to obtain a new traversal block. When the left side of the search frame coincides with the left side of the speckle interferogram, the search frame is moved by 1 pixel distance upwards to obtain a new traversal block. Then, the search frame is gradually moved to the right by 1 pixel distance to obtain a new traversal block. The above steps are repeated until the upper right corner of the search frame coincides with the upper right corner of the speckle interferogram, and the traversal is completed. The step distance can be set according to requirements, such as 2 pixels, 3 pixels, etc. In the embodiment, the details are not described again.

[0085] The speckle interference pattern corresponding to the selected block can be a speckle interference pattern obtained before deformation of the measured object, or can be a speckle interference pattern obtained after deformation of the measured object, without affecting the speckle interferometry, and the center coordinates of the selected block coincide with the origin of the two-dimensional coordinate system.

[0086] It should be noted that in this document, the terms "comprising", "containing", or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, article or device that includes a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, method, article or device. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0087] The above examples are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent substitutions for part of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A speckle interferometry system, characterized in that: It includes a parallel light generating device for generating parallel light; Part of the parallel light is reflected by the reflector 1 and then irradiated on the beam splitter prism 1, and is split into the reflected light 1 and the transmitted light by the beam splitter prism 1; Part of the reflected light 1 is irradiated on the measured surface and diffusely reflected to form reflected light 2; Partially reflected light 2 passes through beam splitter prism 1, Fourier lens 1, aperture, Fourier lens 2, and beam splitter prism 2 in sequence, and then illuminates the camera imaging surface as object light; Part of the transmitted light is reflected by the second reflector, the third reflector and the second beam splitter prism in sequence, and then irradiates the camera imaging surface as reference light; Among them, Fourier lens 1 and Fourier lens 2 form a 4f system, the measured surface is on the front focal plane of Fourier lens 1, the camera imaging surface is on the back focal plane of Fourier lens 2, and the aperture is on the spectrum plane of the 4f system; The method for performing speckle interferometry using the system includes: Obtain two pairs of speckle interferograms before and after deformation of the measured surface in the same coordinate system; Get the amplitude correlation coefficient of each element in the search set and the selected block ,and , is the statistical average, is the conjugate operation; is the coordinate of a point in a two-dimensional coordinate system on the camera imaging surface, and the origin of the two-dimensional coordinate system is the intersection of the optical axis and the camera imaging surface in the 4f system; is the complex amplitude of the object light in the selected block, is the complex amplitude of the object light in the traversal block; the selected block is obtained by selecting the search box in the speckle interferogram obtained before the measured surface is deformed, and the traversal block is obtained by selecting the search box in the speckle interferogram obtained after the measured surface is deformed according to the set traversal rules. All traversal blocks selected by the search box in the speckle interferogram obtained after the measured surface is deformed according to the set traversal rules constitute the search set; Then obtain the traversal block corresponding to the maximum value of all amplitude correlation coefficients and use it as the offset block; Obtain a corrected interferogram obtained after the interferogram corresponding to the traversed block is offset, and the center coordinates of the offset block in the corrected interferogram are the same as the center coordinates of the selected block; The out-of-plane deformation of the measured surface is calculated using the corrected interference pattern and the corresponding interference pattern of the selected block.

2. The speckle interferometry system according to claim 1, characterized in that: The diaphragm is an aperture diaphragm with adjustable aperture.

3. The speckle interferometry system according to claim 1, characterized in that: The second reflector is connected to a driving structure 1 for adjusting its reflection angle.

4. The speckle interferometry system according to claim 1, characterized in that: The reflector 3 is connected to a driving structure 2 for adjusting its reflection angle.

5. The speckle interferometry system according to claim 1, characterized in that: The parallel light generating device includes a laser and a collimating beam expander, and the laser light generated by the laser is expanded by the collimating beam expander and then irradiated on the first beam splitter prism as parallel light.

6. The speckle interferometry system according to claim 1, characterized in that: The center coordinates of the selected block coincide with the origin of the two-dimensional coordinate system.

7. The speckle interferometry system according to claim 1, characterized in that: The speckle interferogram corresponding to the selected block is the speckle interferogram obtained before the measured surface is deformed.

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