Dual-band laser shearing speckle interference measurement system and measurement method

Abstract

The invention relates to a dual-band laser shearing speckle interference measurement system and a measurement method. The system comprises a dual-band laser light source, paraxial and coaxial illumination modules, a shearing module (independently adjusting the shearing amount in the X / Y direction), a phase shift module, a 4f image transmission system (comprising an optical path compensation plate), a dichroic beam splitter prism and a dual-image acquisition unit. Through synchronous illumination of a dual-band light source, light path consistency is ensured in combination with an optical path compensation design, and synchronous high-resolution measurement of the X / Y direction deformation first-order derivative of a to-be-measured sample is realized. The method comprises the steps of pixel calibration, shearing amount dynamic adjustment, phase resolving, deformation derivative calculation, optimal displacement determination and the like, and supports static and quasi-static deformation real-time monitoring. According to the invention, the spatial resolution, the measurement range and the measurement sensitivity are improved through dual-band synchronous measurement; dynamically adjusting the shear amount to expand the measurement range; the device is suitable for samples with different sizes and scattering characteristics, and is suitable for high-precision deformation analysis in the fields of industrial detection, precision manufacturing and scientific research.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology and relates to a dual-band laser shear speckle interferometry measurement system and method. Background Technology

[0002] Laser speckle interferometry, as an interferometric measurement technique, is mainly used for non-smooth surface objects. It generates a laser speckle field by combining it with a scattering screen, etc. It can also be used for smooth surface objects to measure the deformation and first derivative of the object under operating conditions. It is used for thermodynamic performance analysis, mass status monitoring, vibration analysis, etc., and has the advantages of full field, non-contact, high precision, high sensitivity, and anti-interference.

[0003] According to the measurement principle, laser shear speckle interferometry can be divided into time phase shift and spatial phase shift. Among them, time phase shift uses phase shifting devices such as PZT to obtain a series of shear speckle interferograms step by step, which is suitable for static and quasi-static measurements, with high spatial resolution and a large dynamic measurement range. Spatial phase shift is achieved by introducing a carrier frequency, and the object light spectrum and background light spectrum are separated by single-frame image processing, which is suitable for dynamic and transient measurements, but has low spatial resolution and a small dynamic measurement range. Zhou et al. combined the time phase shift method and used a speckle and shear speckle dual-function optical path system to perform time-division measurement of outward displacement and first-order displacement derivative (Prior Technology 1, Journal of Modern Optics, 69(3), 2022); Xie et al. proposed a spatial phase shift shear speckle interferometer based on a 4f system, which placed an aperture in front of the imaging lens to introduce a carrier, and obtained the first-order displacement derivative information at the honeycomb plate defect by adjusting the reflector to separate the spectrum (Prior Technology 2, Applied optics, 52(17), 2013). Wu Minyang et al. proposed a dual-wavelength laser shear speckle interferometry method based on a color camera for synchronously measuring the in-plane and out-of-plane displacement derivatives of deformable objects (Prior Technology 3, Acta Optica Sinica, 40(18), 2020); Wang et al. used a Roger polarizing lens, combined with the space carrier method and color CCD, and applied the finite element analysis method to realize the synchronous measurement of six first-order displacement derivatives in and out of the plane (Prior Technology 4, IEEE Transactions on Instrumentation and Measurement, 70, 2021).

[0004] However, most existing in-plane and out-of-plane multi-channel first-order displacement derivative measurement systems employ the space carrier method to extract phase, resulting in low spatial resolution and easy loss of low-frequency phase information. They also suffer from small dynamic range and low measurement accuracy. Furthermore, existing solutions are often designed for specific objects or application scenarios, lacking sufficient compatibility and failing to meet diverse application needs. Therefore, exploring measurement methods with higher resolution, wider dynamic range, and higher accuracy, as well as improving the compatibility of technical solutions, have become critical issues that urgently need to be addressed in this field. Summary of the Invention

[0005] To address the issues of low spatial resolution, small dynamic range, and insufficient compatibility in the existing technologies, this invention provides a dual-band laser shear speckle interferometry system and method, which enables high-resolution, in-situ real-time monitoring of samples with different surface scattering rates under conditions of different sizes and working distances.

[0006] The technical solution of the present invention is as follows:

[0007] A dual-band laser shear speckle interferometry system includes:

[0008] A dual-band laser source is used to output laser beams with wavelengths of λ1 and λ2, where λ1 ≠ λ2.

[0009] Paraxial illumination module and coaxial illumination module are used to collimate, expand and illuminate the laser beams of wavelengths λ1 and λ2 onto the sample to be tested;

[0010] An imaging unit is used to image the surface of the sample to be tested. The image plane of the imaging unit coincides with the object plane of the first image transfer mirror group.

[0011] The shearing module includes at least two dichroic mirrors and a drive motor for independently adjusting the shearing amount in the X and Y directions;

[0012] The phase shift module includes at least two dichroic mirrors and a phase shifter for implementing time phase shifting;

[0013] The 4f image transfer system consists of a first image transfer mirror group and a second image transfer mirror group. It is used to transfer the image from the imaging unit to the image acquisition unit and to balance the optical path from the first image transfer mirror group to the imaging unit and the optical path from the second image transfer mirror group to the image acquisition unit through an optical path compensation plate.

[0014] The beam splitting unit is used to split the laser beam into two beams, which are then input into the shearing module and the phase shifting module, respectively.

[0015] A dichroic beam splitter is used to separate laser beams of wavelengths λ1 and λ2 and guide them to the first image acquisition unit and the second image acquisition unit, respectively.

[0016] The dual image acquisition unit, consisting of a first image acquisition unit and a second image acquisition unit, is located on the image plane of the second image transfer mirror group and is used to record laser interference images with wavelengths λ1 and λ2, respectively.

[0017] The collimated light source module includes a first collimated light source and a second collimated light source located on both sides of the imaging unit, with a center wavelength of λ1 or λ2, and is used to calibrate the pixel size and effective field of view of the image acquisition unit.

[0018] A computer is used to control the laser source, shearing module, phase shifting module and image acquisition unit, and to calculate the first derivative of the deformation of the sample in the X / Y direction.

[0019] The dual-band laser source is a single-mode, multi-mode, narrow-linewidth, or semiconductor laser, output through an optical fiber, and the power of λ1 and λ2 can be adjusted independently.

[0020] The paraxial illumination module includes a paraxial fiber collimator, a paraxial mirror group, and a paraxial laser beam expander. The coaxial illumination module includes a coaxial fiber collimator, a coaxial mirror group, a coaxial laser beam expander, and a polarization beam splitter coaxially. The fiber optic connectors of the paraxial fiber collimator and the coaxial fiber collimator are the same.

[0021] The laser incident surface of the dichroic beam splitter is coated with antireflective films of λ1 and λ2, the exit surface of the first image acquisition unit is coated with a bandpass film with a center wavelength of λ1, and the exit surface of the second image acquisition unit is coated with a bandpass film with a center wavelength of λ2.

[0022] The optical properties of the first dichroic mirror in the shearing module and the third dichroic mirror in the phase-shifting module are transmission wavelength λ1 and reflection wavelength λ2, respectively, and their optical paths are equal relative to the dichroic beam splitter prism; the optical properties of the second dichroic mirror in the shearing module and the fourth dichroic mirror in the phase-shifting module are transmission wavelength λ2 and reflection wavelength λ1, respectively, and their optical paths are equal relative to the dichroic beam splitter prism.

[0023] The thickness of the optical path compensation plate is determined based on the optical path difference calculation, so that the optical path from the first image transfer mirror group to the imaging unit, the optical path from the second image transfer mirror group to the first image acquisition unit, and the optical path from the second image transfer mirror group to the second image acquisition unit are all equal.

[0024] The present invention also provides a method for synchronously measuring the first derivative of deformation in the X / Y directions using the above-mentioned dual-band laser shear speckle interferometry system, comprising the following steps:

[0025] ① Set the center wavelength of the first collimating light source and the second collimating light source to λ1 or λ2, and turn them on to illuminate the sample to be tested;

[0026] ② Calibrate the pixel size and effective field of view of the first image acquisition unit recording the image or the second image acquisition unit, which has the same center wavelength as the first and second collimated light sources:

[0027] ③ Adjust the tilt angles α and β in the X and Y directions of the shearing module, and calculate the shear amount S in the X and Y directions respectively. x and S y ;

[0028] ④ Turn off the first and second collimating light sources, and turn on the laser light source to illuminate the sample to be tested;

[0029] ⑤ A four-step equidistant time phase shift method is adopted, using the first image acquisition unit to record images and the second image acquisition unit to acquire dual-band interferometric image sequences;

[0030] ⑥ Extract the phase difference in the X and Y directions from the dual-band interferometric image sequence, perform noise filtering and unwrapping processing to obtain the phase distribution, and calculate the first derivative of deformation based on the shearing amount in the X and Y directions.

[0031] Furthermore, step ② specifically includes:

[0032] Extract the beam centers of the two collimated light sources from the image recorded by the first image acquisition unit or the image of the second image acquisition unit, and calculate the actual size of each pixel P = L / num, where L is the actual distance between the two collimated light sources and num is the number of pixels between the beam centers.

[0033] Based on the number of pixels [m, n] in the X and Y directions of the image recorded by the first image acquisition unit or the second image acquisition unit, calculate the effective detection field of view size [P, PP].

[0034] Furthermore, step ③ specifically includes:

[0035] By controlling the drive motor to adjust the first and second dichroic mirrors, the first dichroic mirror is tilted at an angle α along the X direction and the second dichroic mirror is tilted at an angle β along the Y direction, and the image acquired by the first or second image acquisition unit after tilting is recorded.

[0036] Extract the beam center of each collimated light source and its translated beam center from the tilted image, and calculate the shearing amount S in the X direction. x S represents the shear quantities in the N and Y directions. y For S x× shear β / tanα, where N is the average number of pixels N=(N1+N2) / 2, and N1 and N2 are the number of pixels at the center-to-center distance of the first collimated beam and the number of pixels at the center-to-center distance of the second collimated beam, respectively.

[0037] Furthermore, step ⑤ specifically includes:

[0038] Adjust the parameters of the first and second image acquisition units to ensure clear imaging of the sample under test. The first image acquisition unit acquires images in the X direction, and the second image acquisition unit acquires images in the Y direction. Set the displacement ΔL, then the phase change in the optical path of the two image acquisition units is... Set the acquisition cycle interval T and the interval t between a single phase shift and image acquisition;

[0039] The initial phase-shift motion is performed using a computer-controlled phase-shift module, and images are acquired after each motion. After four equally spaced phase shifts, the image recorded by the first image acquisition unit is I. x10 I x20 I x30 I x40 The image recorded by the second image acquisition unit is I. y10 I y20 I y30 I y40 ;

[0040] If the sample under test continues to change, the phase shift motion and image acquisition are repeated with a time interval T. After the i-th four-step equally spaced phase shift, the images of the first image acquisition unit are recorded as I. x1i I x2i I x3i I x4i The images from the second image acquisition unit are recorded as I. y1i I y2i I y3i I y4i When T=0, it indicates continuous real-time recording.

[0041] Furthermore, step ⑥ specifically includes:

[0042] Phase information in the X and Y directions is extracted from the images of the first image acquisition unit and the interference image sequence of the second image acquisition unit, respectively;

[0043] The phase difference between the sample and its initial state at any subsequent moment is calculated using the following formula:

[0044] Δφ xi (x,y)=φ xi (x,y)-φ x0 (x,y)

[0045] Δφ yi (x,y)=φ yi (x,y)-φ y0 (x,y)

[0046] The phase difference between any subsequent moment and the previous moment in the sample is calculated using the following formula:

[0047] Δφ' xi (x,y)=φ xi (x,y)-φ x(i-1) (x,y)

[0048] Δφ' yi (x,y)=φ yi (x,y)-φ y(i-1) (x,y)

[0049] - The calculated phase difference is then subjected to noise filtering and unwrapping to obtain the phase distribution φ. xi (x,y), φ yi (x,y), Δφ x ' i (x,y), Δφ' yi (x,y)

[0050] - Calculate the first derivative of deformation in the X / Y directions based on the shear amount in the X and Y directions.

[0051] The first derivative of the deformation w(x,y) in the X / Y directions relative to the initial state at any given time is given by the following formula:

[0052]

[0053] The first derivative of the X / Y deformation W(x,y) at any given moment relative to the previous moment is given by the following formula:

[0054]

[0055] Furthermore, prior to step ①, initial calibration and positioning are also included, specifically including:

[0056] The dual-band laser shear speckle interferometry system is fixed on the detection station to monitor the relative deformation of the object under test at any time.

[0057] Based on the working distance, size, and surface optical scattering characteristics of the object under test, the illumination module and laser source are adapted.

[0058] The sample under test is illuminated by a white light source, and the imaging unit and image acquisition unit are adjusted to make the sample under test clearly imaged.

[0059] The optimal displacement value ΔL is obtained by the following method:

[0060] Because the two laser wavelengths are different, random noise in the image will occur during actual use. n Displacement error ΔL e Factors such as displacement directly affect the accuracy of phase measurement. Therefore, a method for determining the optimal displacement has been developed, and the specific steps are as follows:

[0061] 1. Displacement ΔL0 = Δl + K × R, where Δl is the initial displacement, R is the minimum single displacement of the phase shift module, and K is an integer (K ​​= 0, 1, 2, 3, ...).

[0062] 2. Based on the displacement error ΔL of the phase shift module e Displacement error ΔL for each time ek In 0~ΔL e Between k = 1, 2, 3, 4, the actual displacement for the four cycles is 2 × (ΔL0 + ΔL) ek The corresponding phase change is 4π / λ1×(ΔL0+ΔL). ek ), 4π / λ2×(ΔL0+ΔL ek );

[0063] 3. Set image random noise I nxk I nyk In 0~I n between;

[0064] 4. Set the phase value to be measured to be... The intensity image acquired after each phase shift in the X direction is represented as follows:

[0065]

[0066] in, I' x ' k (x,y)=2E0(x,y)E0(x+S x E0(x,y) is the complex amplitude of the optical field in the reference optical path, and E0(x+S) is the amplitude of the optical field in the reference optical path. x (x, y) represents the complex amplitude of the optical field shearing the optical path in the X direction. When determining the displacement, the X and Y directions are set to be equal. Similarly, the intensity image acquired after each phase shift in the Y direction can be obtained.

[0067]

[0068] in, I” yk (x,y)=2E0(x,y)E0(x,y+S y ), E0(x,y+S yThe intensity image above is the complex amplitude of the optical field sheared along the Y-direction. Phase extraction is performed on the intensity image to obtain phase measurements in the X and Y directions.

[0069] 5. Calculate the error between the phase value to be measured and the phase measurement values ​​in the X and Y directions, respectively.

[0070] 6. Repeat steps 1 to 5. When ΔL0 ≥ min[λ1 / 4, λ2 / 4], execute step 7.

[0071] 7. Plot ΔL0 as the x-axis, Plot the relationship curve between displacement and phase error on the vertical axis, and select the displacement corresponding to the smaller phase error as the optimal displacement ΔL.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] 1) This invention adopts the technical solution of "dual-band laser light source + 4f system image transmission + equal step time phase shift + independent adjustment of orthogonal shearing direction + dual detectors" to realize synchronous real-time and high-resolution measurement of the first derivative of the deformation of the target under test in the X and Y directions;

[0074] 2) Based on the size, optical scattering characteristics, and detection distance of the target under test, the optical and mechanical interfaces of the illumination module and the laser source were unified, expanding the system's applicability and application scenarios;

[0075] 3) In terms of image transfer in the 4f system, a compensation plate was used to adjust the optical path from the image transfer mirror group to the imaging unit, so that its optical path is equal to that from the image transfer mirror group to the image acquisition unit, thereby ensuring that the parameters of the two image transfer mirror groups are consistent, reducing the difficulty and cost of design, manufacturing and assembly.

[0076] 4) By designing the optical elements of the same laser band in the shearing module and the phase shifting module as equal optical path interference, the coherence length requirement of the laser source is reduced. Therefore, single-mode, multi-mode, narrow-linewidth or semiconductor lasers can meet the requirements, which improves the applicability of the system and reduces the system cost.

[0077] 5) It has the functions of calibrating and adjusting the measurement field of view and shear amount, which makes it easy to adapt different shear amounts according to the deformation range of the target to be measured, thus improving the strain measurement range and measurement sensitivity.

[0078] 6) To address the phase extraction errors caused by factors such as environmental noise and displacement errors, a method for determining the optimal displacement in a dual-band laser equal-step phase extraction algorithm is proposed, which improves the accuracy of phase information measurement. Attached Figure Description

[0079] Figure 1This is a schematic diagram of an embodiment of the dual-band laser shearing speckle interferometry measurement system of the present invention.

[0080] Figure 2 This is the curve showing the relationship between displacement and phase error in the embodiment.

[0081] Figure 3 This is the encapsulation phase diagram at three moments relative to the initial state during X-direction shearing (532nm) in the embodiment.

[0082] Figure 4 yes Figure 3 The deformation first derivative is calculated by unwrapping the wrapped phase map and combining it with the shear calibration results.

[0083] Figure 5 This is the encapsulation phase diagram at three moments relative to the initial state during Y-direction shearing (639nm) in the embodiment.

[0084] Figure 6 yes Figure 5 The deformation first derivative is calculated by unwrapping the wrapped phase map and combining it with the shear calibration results. Detailed Implementation

[0085] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention.

[0086] Please see Figure 1 , Figure 1 This is a schematic diagram of an embodiment of the dual-band laser shearing speckle interferometry system of the present invention. As shown in the figure, a dual-band laser shearing speckle interferometry system includes:

[0087] The laser source 13 is used to provide dual-band laser beam output. The type is single-mode, multi-mode, narrow-linewidth, or semiconductor laser, etc. The output laser wavelengths are λ1 and λ2. It adopts fiber optic output and is coupled to the paraxial illumination module 1 or the coaxial illumination module 2. The fiber optic connector is matched with the fiber optic connector of the paraxial fiber collimator 101 and the coaxial fiber collimator 201. The laser power of each band can be independently controlled and adjusted.

[0088] The illumination module includes a paraxial illumination module 1 and a coaxial illumination module 2, which are used to collimate, transmit, and expand two laser beams with wavelengths λ1 and λ2, respectively, and to illuminate the sample 17 under test. The choice of paraxial illumination module, coaxial illumination module, or a combination thereof is determined based on factors such as the size of the sample under test, its surface optical scattering characteristics, the detection distance, and the detection parameters. Paraxial illumination module 1 includes a paraxial fiber collimator 101, a paraxial first reflector 102, a paraxial second reflector 103, and a paraxial laser beam expander 104. Coaxial illumination module 2 includes a coaxial fiber collimator 201, a coaxial first reflector 202, a coaxial second reflector 203, a coaxial laser beam expander 204, and a polarization beam splitter 205. The fiber optic connectors of the paraxial fiber collimator 101 and the coaxial fiber collimator 201 are the same.

[0089] Imaging unit 3 is used to image the sample to be tested. The image plane of the imaging unit coincides with the object plane of the first image transfer mirror group 5. The imaging unit has a mechanical interface for installing the coaxial illumination module 2.

[0090] The compensation plate 4 is used to increase the optical path from the first image transfer mirror group 5 to the imaging unit 3, so that its optical path is equal to the optical path from the second image transfer mirror group 9 to the first image acquisition unit 11 and the optical path from the second image transfer mirror group 9 to the second image acquisition unit 12, thereby ensuring that the parameters of the two image transfer mirror groups are consistent and reducing the difficulty of design, manufacturing and assembly.

[0091] The first image transfer mirror group 5 and the second image transfer mirror group 9 form a 4f system, which is used to transfer the image of the imaging unit 3 to the first image acquisition unit 11 and the second image acquisition unit 12.

[0092] The beam splitting unit 6 is used to split the laser beam into two laser beams of equal intensity, which are used for the shearing module (7) and the phase shifting module 8, respectively.

[0093] The shearing module 7 includes a first dichroic mirror 701, a second dichroic mirror 702, and a drive motor 703, which are used to electrically and independently adjust the shearing amount in the X and Y directions; the shearing interference is used to generate a speckle pattern containing deformation information.

[0094] The phase shift module 8 includes a third dichroic mirror 801, a fourth dichroic mirror 802, and a phase shifter 803, which are used to achieve time phase shift; phase shift interference is used to improve measurement accuracy and stability.

[0095] Among them, the first dichroic mirror 701 and the third dichroic mirror 801 have the same optical performance, with a transmission wavelength of λ1 and a reflection wavelength of λ2, and the first dichroic mirror 701 and the third dichroic mirror 801 have equal optical paths relative to the beam splitting unit (6); the second dichroic mirror 702 and the fourth dichroic mirror 4802 have the same optical performance, with a transmission wavelength of λ2 and a reflection wavelength of λ1, and the second dichroic mirror 702 and the fourth dichroic mirror 4802 have equal optical paths relative to the beam splitting unit 6.

[0096] A dichroic beam splitter 10 is used to separate laser beams with wavelengths λ1 and λ2, so that they reach the first image acquisition unit 11 and the second image acquisition unit 12 respectively. The laser incident surface of the dichroic beam splitter 10 is coated with anti-reflection films of λ1 and λ2. The exit surface of the first image acquisition unit 11 is coated with a bandpass film with a center wavelength of λ1. The exit surface of the second image acquisition unit 12 is coated with a bandpass film with a center wavelength of λ2.

[0097] The first image acquisition unit 11 and the second image acquisition unit 12 are CMOS, CCD or other photoelectric sensors. The first image acquisition unit 11 records the light intensity signal with a laser wavelength of λ1, and the second image acquisition unit 12 records the light intensity signal with a laser wavelength of λ2. The two are installed on the image plane of the second image transfer mirror group 9. These signals contain deformation information of the surface of the sample to be tested.

[0098] The first collimating light source 14 and the second collimating light source 15 are laser diodes in the same wavelength band, with a center wavelength of λ1 or λ2. They are installed on both sides of the imaging unit 3, and the laser beams of the two light sources are collimated and output in parallel.

[0099] The computer connects to the image acquisition unit, shearing module, phase shift module, and laser light source to control the hardware, acquire, store, and process image data. By comparing and analyzing images from different times or under different conditions, deformation information of the sample surface can be extracted.

[0100] In this embodiment, a dual-band laser source (λ1 = 532nm, λ2 = 639nm) is used. The dual-band laser beam emitted by the laser source is transmitted to the illumination module via optical fiber. The illumination module selects an appropriate illumination method based on the characteristics of the sample to illuminate it. The imaging unit captures an image of the sample and transmits it to the image acquisition unit via an image transfer mirror group. The beam splitting unit divides the laser beam into two beams, which are used for the shearing module and the phase-shifting module, respectively. The shearing module generates a speckle pattern by adjusting the shearing amount, and the phase-shifting module improves measurement accuracy and spatial resolution through time phase shifting. A dichroic beam splitter separates the laser beams of different wavelengths, which are recorded by the two image acquisition units respectively. The computer processes the acquired images to extract minute deformation or displacement information on the sample surface.

[0101] Based on the laser wavelength (λ1 = 532 nm, λ2 = 639 nm) and the displacement error ΔL of the phase shift module... e For 5nm, image noise I n Set the phase difference to 16. Given π and an initial displacement Δl = 30 nm, the relationship curve between displacement and phase error was calculated, and the optimal displacement was determined to be 70 nm.

[0102] Measurement method implementation steps:

[0103] Step 1. System Installation and Initial Calibration

[0104] - Fix the system at the detection station to monitor the deformation W(x,y) of the object to be tested; the sample to be tested (such as a thin metal plate) is placed directly in front of the imaging unit.

[0105] -Based on the working distance, size, and surface optical scattering characteristics of the object under test, an appropriate illumination module and laser source are selected. Paraxial illumination is used for high-scattering surfaces, and coaxial illumination is used for low-scattering surfaces. In this embodiment, the center wavelengths of both the first and second collimated light sources are set to λ1.

[0106] - Illuminate the sample under test with a white light source, and adjust the imaging unit and image acquisition unit to make the sample under test clearly imaged;

[0107] Step 2. Pixel Size and Field of View Calibration

[0108] - Turn on the first collimating light source and the second collimating light source to illuminate the sample to be tested, and use an image acquisition unit with the same working band as the center wavelength of the collimating light source to record the image. In this embodiment, the first image acquisition unit is used.

[0109] - Extract the beam centers of the two collimated light sources in the image and calculate the number of pixels num between the beam centers. Based on the actual distance L between the two light sources, calculate the actual pixel size P = L / num in the image acquisition unit. Based on the number of pixels [m, n] in the X and Y directions of the first image acquisition unit, calculate the effective detection field of view size [P mentioned, PP mentioned] of the first image acquisition unit recording the image or the second image acquisition unit.

[0110] Step 3. Dynamic adjustment of shear rate

[0111] - By controlling the drive motor with a computer, the first and second dichroic mirrors are adjusted so that they produce the same tilt angle (α = β) along the X and Y directions respectively, thereby generating shear interference and recording the image of the first image acquisition unit after tilting;

[0112] - Extract the beam center of each collimated light source in the tilted image and its translated beam center, obtain the number of pixels N1 and N2 between the beam centers, calculate the average number of pixels N = (N1 + N2) / 2, then the shearing amount S x =S y =5mm;

[0113] Step 4. Dual-band interferometric image acquisition and phase shifting

[0114] -Turn off the first and second collimating light sources, and turn on the laser light source to illuminate the sample to be tested;

[0115] - Adjust the exposure, gain and other parameters of the first image acquisition unit and the second image acquisition unit to ensure that the sample under test is clearly imaged. The first image acquisition unit is used to acquire the image in the X direction and the second image acquisition unit is used to acquire the image in the Y direction.

[0116] -The optimal displacement ΔL = 70nm, then the phase change in the optical path of the two image acquisition units. The interval time T of the acquisition cycle (T = 10s) and the interval time t between a single phase shift and image acquisition (t = 10ms);

[0117] - The initial phase shift motion is performed using a computer-controlled phase shift module, and an image is acquired after each motion. After four equally spaced phase shifts, the image recorded by the first image acquisition unit is I. x10 I x20 I x30 I x40 The image recorded by the second image acquisition unit is I. y10 I y20 I y30 I y40 ;

[0118] - If the sample under test continues to change, step S10 is repeated with a time interval T as the period for phase shifting and image acquisition. After the i-th four-step equally spaced phase shift, the images of the first image acquisition unit are recorded as I. x1i I x2i I x3i I x4i The images from the second image acquisition unit are recorded as I. y1i I y2i I y3i I y4i When T=0, it indicates continuous real-time recording;

[0119] Step 5. Phase calculation and deformation derivative calculation

[0120] - Extract the phase information in the X and Y directions from the images of the first image acquisition unit and the second image acquisition unit, respectively, using the following formula:

[0121]

[0122] Where (x,y) represents spatial coordinates;

[0123] - Calculate the phase difference of the sample relative to its initial state at any subsequent moment, using the following formula:

[0124] Δφ xi (x,y)=φ xi (x,y)-φ x0 (x,y)

[0125] Δφ yi (x,y)=φ yi (x,y)-φ y0 (x,y)

[0126] The phase difference between any subsequent moment and the previous moment in the sample is calculated using the following formula:

[0127] Δφ' xi (x,y)=φ xi (x,y)-φ x(i-1) (x,y)

[0128] Δφ' yi (x,y)=φ yi (x,y)-φ y(i-1) (x,y)

[0129] - The calculated phase difference is then subjected to noise filtering and unwrapping to obtain the phase distribution φ. xi (x,y), φ yi (x,y), Δφ' xi (x,y), Δφ' yi (x,y)

[0130] - Calculate the first derivative of deformation in the X / Y directions based on the shear amount in the X and Y directions.

[0131] The formula for the first derivative of the deformation in the X / Y directions relative to the initial state at any given time is as follows:

[0132]

[0133] The formula for the first derivative of the deformation in the X / Y directions at any given moment relative to the previous moment is as follows:

[0134]

[0135] The above embodiments are merely illustrative examples. Those skilled in the art can adjust the parameters or replace equivalent components according to actual needs, all of which fall within the protection scope of this invention.

Claims

1. A dual-band laser shear speckle interferometry system, characterized in that, include: A dual-band laser source is used to output laser beams with wavelengths of λ1 and λ2, respectively, where λ1 ≠ λ2. Paraxial illumination module and coaxial illumination module are used to collimate, expand and illuminate the laser beams of wavelengths λ1 and λ2 onto the sample to be tested; An imaging unit is used to image the surface of the sample to be tested. The image plane of the imaging unit coincides with the object plane of the first image transfer mirror group. The shearing module includes at least two dichroic mirrors and a drive motor for independently adjusting the shearing amount in the X and Y directions; The phase shift module includes at least two dichroic mirrors and a phase shifter for implementing time phase shifting; The 4f image transfer system consists of a first image transfer mirror group and a second image transfer mirror group. It is used to transfer the image from the imaging unit to the image acquisition unit and to balance the optical path from the first image transfer mirror group to the imaging unit and the optical path from the second image transfer mirror group to the image acquisition unit through an optical path compensation plate. The beam splitting unit is used to split the laser beam into two beams, which are then input into the shearing module and the phase shifting module, respectively. A dichroic beam splitter is used to separate laser beams of wavelengths λ1 and λ2 and guide them to the first image acquisition unit and the second image acquisition unit, respectively. The dual image acquisition unit, consisting of a first image acquisition unit and a second image acquisition unit, is located on the image plane of the second image transfer mirror group and is used to record laser interference images with wavelengths λ1 and λ2, respectively. The collimated light source module includes a first collimated light source and a second collimated light source located on both sides of the imaging unit, with a center wavelength of λ1 or λ2, and is used to calibrate the pixel size and effective field of view of the image acquisition unit. A computer is used to control the laser source, shearing module, phase shifting module and image acquisition unit, and to calculate the first derivative of the deformation of the sample in the X / Y direction.

2. The dual-band laser shearing speckle interferometry system according to claim 1, characterized in that, The dual-band laser source is a single-mode, multi-mode, narrow-linewidth, or semiconductor laser, output through an optical fiber, and the power of λ1 and λ2 can be adjusted independently.

3. The dual-band laser shearing speckle interferometry system according to claim 1, characterized in that, The paraxial illumination module includes a paraxial fiber collimator, a paraxial mirror group, and a paraxial laser beam expander. The coaxial illumination module includes a coaxial fiber collimator, a coaxial mirror group, a coaxial laser beam expander, and a polarization beam splitter coaxially. The fiber optic connectors of the paraxial fiber collimator and the coaxial fiber collimator are the same.

4. The dual-band laser shearing speckle interferometry system according to claim 1, characterized in that, The laser incident surface of the dichroic beam splitter is coated with antireflective films of λ1 and λ2, the exit surface of the first image acquisition unit is coated with a bandpass film with a center wavelength of λ1, and the exit surface of the second image acquisition unit is coated with a bandpass film with a center wavelength of λ2.

5. The dual-band laser shearing speckle interferometry system according to claim 1, characterized in that, The optical properties of the first dichroic mirror in the shearing module and the third dichroic mirror in the phase-shifting module are transmission wavelength λ1 and reflection wavelength λ2, respectively, and their optical paths are equal relative to the dichroic beam splitter prism; the optical properties of the second dichroic mirror in the shearing module and the fourth dichroic mirror in the phase-shifting module are transmission wavelength λ2 and reflection wavelength λ1, respectively, and their optical paths are equal relative to the dichroic beam splitter prism.

6. The dual-band laser shearing speckle interferometry system according to claim 1, characterized in that, The thickness of the optical path compensation plate is determined based on the optical path difference calculation, so that the optical path from the first image transfer mirror group to the imaging unit, the optical path from the second image transfer mirror group to the first image acquisition unit, and the optical path from the second image transfer mirror group to the second image acquisition unit are all equal.

7. A method for synchronously measuring the first derivative of deformation in the X / Y directions using the dual-band laser shear speckle interferometry system according to any one of claims 1-6, characterized in that, Includes the following steps: ① Set the center wavelength of the first collimating light source and the second collimating light source to λ1 or λ2, and turn them on to illuminate the sample to be tested; ② Calibrate the pixel size and effective field of view of the first image acquisition unit recording the image or the second image acquisition unit, which has the same center wavelength as the first and second collimated light sources: ③ Adjust the tilt angles α and β in the X and Y directions of the shearing module, and calculate the shear amount S in the X and Y directions respectively. x and S y ; ④ Turn off the first and second collimating light sources, and turn on the laser light source to illuminate the sample to be tested; ⑤ A four-step equidistant time phase shift method is adopted, using the first image acquisition unit to record images and the second image acquisition unit to acquire dual-band interferometric image sequences; ⑥ Extract the phase difference in the X and Y directions from the dual-band interferometric image sequence, perform noise filtering and unwrapping processing to obtain the phase distribution, and calculate the first derivative of deformation based on the shearing amount in the X and Y directions.

8. The method for synchronous measurement of the first derivative of deformation in the X / Y directions according to claim 7, characterized in that, Step ② specifically includes: Extract the beam centers of the two collimated light sources from the image recorded by the first image acquisition unit or the image of the second image acquisition unit, and calculate the actual size of each pixel P = L / num, where L is the actual distance between the two collimated light sources and num is the number of pixels between the beam centers. Based on the number of pixels [m, n] in the X and Y directions of the image recorded by the first image acquisition unit or the second image acquisition unit, calculate the effective detection field of view size [Pcalculated, PPcalculated].

9. The method for synchronously measuring the first derivative of deformation in the X / Y directions according to claim 7, characterized in that, Step ③ specifically includes: By controlling the drive motor to adjust two dichroic mirrors, one dichroic mirror is tilted at an angle α along the X direction and the other dichroic mirror is tilted at an angle β along the Y direction. The image acquired by the first image acquisition unit or the second image acquisition unit after tilting is recorded. Extract the beam center of each collimated light source and its translated beam center from the tilted image, and calculate the shearing amount S in the X direction. x S represents the shear quantities in the N and Y directions. y For S x × shearing amount β / tanα, where N is the average number of pixels N=(N1+N2) / 2, and N1 and N2 are the number of pixels at the center-to-center distance of the first collimated beam and the number of pixels at the center-to-center distance of the second collimated beam, respectively.

10. The method for synchronously measuring the first derivative of deformation in the X / Y directions according to claim 7, characterized in that, Step ⑥ specifically includes: Adjust the parameters of the first and second image acquisition units to ensure clear imaging of the sample under test. The first image acquisition unit acquires images in the X direction, and the second image acquisition unit acquires images in the Y direction. Set the displacement ΔL, then the phase change in the optical path of the two image acquisition units is... Set the acquisition cycle interval T and the interval t between a single phase shift and image acquisition; The initial phase-shift motion is performed using a computer-controlled phase-shift module, and images are acquired after each motion. After four equally spaced phase shifts, the image recorded by the first image acquisition unit is I. x10 I x20 I x30 I x40 The image recorded by the second image acquisition unit is I. y10 I y20 I y30 I y40 ; If the sample under test continues to change, the phase shift motion and image acquisition are repeated with a time interval T. After the i-th four-step equally spaced phase shift, the images of the first image acquisition unit are recorded as I. x1i I x2i I x3i I x4i The images from the second image acquisition unit are recorded as I. y1i I y2i I y3i I y4i When T=0, it indicates continuous real-time recording.

11. The method for synchronously measuring the first derivative of deformation in the X / Y directions according to claim 9, characterized in that, Step ⑥ specifically includes: Phase information in the X and Y directions is extracted from the images of the first image acquisition unit and the interference image sequence of the second image acquisition unit, respectively; The phase difference between the sample and its initial state at any subsequent moment is calculated using the following formula: Df xi (x,y)=φ xi (x,y)-φ x0 (x,y) Df yi (x,y)=φ yi (x,y)-φ y0 (x,y) The phase difference between any subsequent moment and the previous moment in the sample is calculated using the following formula: Df' xi (x,y)=φ xi (x,y)-φ x(i-1) (x,y) Df' yi (x,y)=φ yi (x,y)-φ y(i-1) (x,y) - The calculated phase difference is then subjected to noise filtering and unwrapping to obtain the phase distribution φ. xi (x,y), φ yi (x,y), Δφ′ xi (x,y), Δφ' yi (x,y) - Calculate the first derivative of deformation in the X / Y directions based on the shear amount in the X and Y directions. The first derivative of the deformation w(x,y) in the X / Y directions relative to the initial state at any given time is given by the following formula: The first derivative of the X / Y deformation W(x,y) at any given moment relative to the previous moment is given by the following formula:

12. The method for synchronously measuring the first derivative of deformation in the X / Y directions according to any one of claims 7-9, characterized in that, Prior to step ①, initial calibration and positioning are also included, specifically including: The dual-band laser shear speckle interferometry system is fixed on the detection station to monitor the deformation W(x,y) of the object under test. Based on the working distance, size, and surface optical scattering characteristics of the object under test, the illumination module and laser source are adapted. The sample under test is illuminated by a white light source, and the imaging unit and image acquisition unit are adjusted to make the sample under test clearly imaged.

13. The method for synchronously measuring the first derivative of deformation in the X / Y directions according to claim 10, wherein the step of determining the optimal value of the displacement ΔL includes: ① Displacement ΔL0=Δl+K×R, where Δl is the initial displacement, R is the minimum single displacement of the phase shift module, and K is an integer (K=0, 1, 2, 3, …); ②Based on the displacement error ΔL of the phase shift module e Displacement error ΔL for each time ek In 0~ΔL e Between k = 1, 2, 3, 4, the actual displacement for the four cycles is 2 × (ΔL0 + ΔL) ek The corresponding phase change is 4π / λ1×(ΔL0+ΔL). ek ), 4π / λ2×(ΔL0+ΔL ek ); ③ Set image random noise I nxk I nyk In 0~I n between; ④ Set the phase value to be measured to be... The intensity image acquired after each phase shift in the X direction is represented as follows: in, I″ xk (x,y)=2E0(x,y)E0(x+S x E0(x,y) is the complex amplitude of the optical field in the reference optical path, and E0(x+S) is the amplitude of the optical field in the reference optical path. x (x, y) represents the complex amplitude of the optical field shearing the optical path in the X direction. When determining the displacement, the X and Y directions are set to be equal. Similarly, the intensity image acquired after each phase shift in the Y direction can be obtained. in, I″ yk (x,y)=2E0(x,y)E0(x,y+S y ), E0(x,y+S y The intensity image above is the complex amplitude of the optical field sheared along the Y-direction. Phase extraction is performed on the intensity image to obtain phase measurements in the X and Y directions. ⑤ Calculate the error between the phase value to be measured and the phase measurement values ​​in the X and Y directions, respectively. ⑥ Repeat steps ① to ⑤, and execute step ⑦ when ΔL0 ≥ min[λ1 / 4, λ2 / 4]; ⑦ Using ΔL0 as the x-coordinate, Plot the relationship curve between displacement and phase error on the vertical axis, and select the displacement corresponding to the smaller phase error as the optimal displacement ΔL.

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