Three-dimensional measuring device and method for residual stress inside glass

Abstract

A three-dimensional measurement device and method for residual stress inside glass includes: an illumination system, a two-dimensional scanning system, a dark field generation system, a sample to be tested, and a data acquisition system. The illumination system consists of a light source and a collimation system to provide illumination for the sample to be tested. The two-dimensional scanning system is a small aperture that can move two-dimensionally. The dark field generation system consists of two linear polarization devices with mutually perpendicular light transmission directions that can rotate synchronously. The sample to be tested is a transparent optical element placed in the dark field generation system. The data acquisition system is used to record experimental data. A matching algorithm is used to develop a three-dimensional polarization stacked diffraction imaging technique to reconstruct the residual stress distribution in the sample to be tested in three dimensions. The three-dimensional stress measurement method proposed in this invention is easy to operate, provides high accuracy in calculation results, and can meet the requirements for three-dimensional measurement of residual stress inside large-aperture optical elements.

Description

Technical Field

[0001] This invention relates to the field of stress birefringence measurement, and in particular to a three-dimensional measuring device and method for residual stress inside glass. Background Technology

[0002] Residual stress is generated during the forming, annealing, cutting, polishing, coating, and repair processes of optical components, leading to internal defects. Polarized beams passing through these defects experience wavefront distortion due to birefringence, affecting beam quality and reducing the performance of the optical components. Therefore, accurately measuring the location and magnitude of residual stress can guide improvements in material growth and component repair techniques, and predict the trajectory of internal defects in optical materials. Furthermore, observing the birefringence properties of biological metabolites can be used for disease diagnosis and cancer cell screening.

[0003] In general, stress varies along the optical path, so reconstructing the internal structural information of a sample requires three-dimensional photoelastic data. Several three-dimensional measurement techniques exist, including the finite element method, frozen stress slicing, etching, integrated photoelasticity, tomography, and Fourier transform. However, the finite element method cannot obtain experimental parameters that perfectly match reality and can only serve as a reference for practical operation. Frozen stress slicing and etching can cause irreversible damage to materials, so they are rarely used in the measurement of large optical components and living samples. Integrated photoelasticity requires converting the three-dimensional photoelastic model into an equivalent optical model containing a linear phase retarder and a rotator, making theoretical analysis complex. Tomography offers high imaging accuracy, but the measurement process requires multiple changes to the relative position of the sample and the probe light, resulting in a large amount of data and a complex reconstruction process. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a three-dimensional measurement device and method for residual stress inside glass. This method utilizes a high-quality dark field to acquire photoelastic information within the glass and combines this with the proposed three-dimensional polarization stacked diffraction imaging technique to calculate the distribution of parameters such as three-dimensional phase difference, optical path difference, and principal stress difference within the sample. This measurement device and method can be applied to the three-dimensional measurement of stress birefringence. The dark field distribution at three angles is recorded by scanning. First, the photoelastic information at each angle is reconstructed layer by layer. Then, the stress distribution inside the optical element is reconstructed three-dimensionally using the phase-shifting method to obtain the axial position of the stress within the optical element. The axial resolution is 6 mm, and the optical path difference measurement accuracy is at the nanometer level.

[0005] The technical solution of the present invention is as follows:

[0006] On one hand, the present invention provides a three-dimensional measuring device for residual stress inside glass, characterized in that it includes:

[0007] A light source used to emit circularly polarized light;

[0008] A collimation system, located after the light source, is used to collimate and expand the light emitted by the light source;

[0009] A two-dimensional scanning system is used to cut the beam collimated and expanded by the collimation system into a small-aperture beam and to perform two-dimensional scanning on the surface of the sample to be tested.

[0010] A polarizer, located after the two-dimensional scanning system, is used to convert the light beam into illumination light with a specific polarization state;

[0011] An analyzer is positioned after the polarizer and perpendicular to the light transmission direction of the polarizer. The two rotate synchronously to create dark field conditions.

[0012] The sample to be tested is placed between the polarizer and the analyzer;

[0013] The data acquisition system is used to acquire and record diffraction spot images at different rotation angles and scanning positions;

[0014] The data processing system, connected to the data acquisition system, processes the diffraction spot image and reconstructs the three-dimensional residual stress distribution map inside the sample under test through an iterative algorithm.

[0015] Furthermore, it also includes a control system, which is connected to the two-dimensional scanning system, the polarizer, and the analyzer respectively, for controlling the polarizer and the analyzer to rotate synchronously to form dark field conditions, and controlling the two-dimensional scanning system to scan once for each rotation angle.

[0016] Preferably, the angle is 30°.

[0017] Preferably, the two-dimensional scanning system is a small aperture with a diameter of 4 mm, which can perform two-dimensional scanning in a plane perpendicular to the beam transmission direction.

[0018] Preferably, the data acquisition system is a high-definition camera with a resolution of not less than 4096×4096.

[0019] Preferably, both the polarizer and the analyzer are linear polarizers with a diameter of 50.8 mm and an extinction ratio of not less than 10000:1.

[0020] Preferably, the collimation system is a lens.

[0021] On the other hand, the present invention also provides a method for measuring residual stress inside glass using the above-mentioned three-dimensional measuring device, characterized in that it includes the following steps:

[0022] Step 1) The circularly polarized light emitted by the light source is collimated by the collimation system and then shines on the two-dimensional scanning system. It moves in two dimensions on the surface of the sample to be tested through the small aperture of the two-dimensional scanning system, cutting out a small-diameter beam for two-dimensional scanning.

[0023] Step 2) Each time, the polarizer and analyzer rotate synchronously at a preset angular interval to maintain dark field conditions;

[0024] Step 3) At each rotation angle, the two-dimensional scanning system performs one two-dimensional scan, and the data acquisition system records the diffraction spot image generated during the scanning process of the two-dimensional scanning system;

[0025] Step 4) Process the acquired diffraction spot image and reconstruct the three-dimensional residual stress distribution map inside the sample under test using an iterative algorithm.

[0026] Preferably, the acquired diffraction spot image is processed, and an iterative algorithm is used to reconstruct the three-dimensional residual stress distribution map inside the sample under test.

[0027] Preferably, the preset angle interval is 30°, that is, π / 6 radians as the interval, and the rotation is performed three times.

[0028] Assuming the collimated illumination light is P0(x,y), the two-dimensional scanning system cuts the illumination light into a small-aperture beam P1(x,y). The dark-field generating device rotates continuously to three angular positions at 30° intervals. At each angular position, the two-dimensional scanning system performs one two-dimensional scan. The data acquisition system records a total of three sets of diffraction spots, denoted as P1(x,y). Ω l =0,π / 6,π / 3, l = 1, 2, 3, A, B represent the number of rows and columns in the scanning array, and there is overlap between adjacent scanning positions, with an overlap rate of approximately 70%. The sample to be tested, with a thickness of h, is placed in the dark field generation system and assumed to be M two-dimensional slices S placed along the optical axis. m (x,y), m=1:M.

[0029] 1) The transmission process of the illumination beam from the two-dimensional scanning system to the data acquisition system can be represented as:

[0030]

[0031] Where P1(x,y) represents the initially guessed complex amplitude distribution of illumination light, and H(x,y) represents the aperture function. This represents the complex amplitude distribution of the M-layer thin sample. Let represent the transmission factor of the convolution kernel in free space, z represent the transmission distance, and -z represent the distance of reverse transmission z. The distance from the two-dimensional scanning system to the front surface of the sample under test is d1, the distance from the first sample layer to the second sample layer is h1, the distance from the second sample layer to the third sample layer is h2, ..., and the distance from the rear surface of the sample under test to the data acquisition system is d2. The illumination light at the ab-th illumination position of the m-th sample layer is... The corresponding transmitted light is Where a = 1:A and b = 1:B represent the coordinates of the diffraction spot in the two-dimensional array.

[0032] 2) Describe the light field on the surface of the data acquisition system in terms of amplitude and phase.

[0033]

[0034] The l-th set of diffraction spot arrays recorded is retrieved, and the three-dimensional reconstruction of the residual stress distribution within the sample is performed. The j-th iteration process is as follows:

[0035] 3) The diffraction spot actually recorded by the data acquisition system is used as a constraint in the iteration process, replacing the amplitude information in the update process. The updated light field distribution is as follows:

[0036]

[0037] 4) The updated light field is transmitted back to the rear surface of the sample, i.e., the transmitted light at the Mth layer of the sample is...

[0038]

[0039] 5) Update the complex amplitude distribution of the M-th layer sample using the following formula.

[0040]

[0041] 6) Update the distribution of each layer of sample in reverse order until the front surface of the sample is reached.

[0042] 7) Update the illumination distribution on the front surface of the sample.

[0043]

[0044] 8) Reverse transmission of illumination light to the position of the two-dimensional scanning system.

[0045]

[0046] Furthermore, the aperture function is incorporated as a constraint condition into the update process to promote function convergence.

[0047]

[0048] 9) Repeat steps 1-8, using the (ab+1)th diffraction spot for updating, until the sample distribution at all illumination positions is updated, and then proceed to the (j+1)th update.

[0049] 10) Obtain the photoelastic parameter distributions of each sample layer at three angles, and denote the intensity distributions as follows: The intensity distribution of the illumination light is I P Then the phase difference caused by stress birefringence on the m-th sample is:

[0050]

[0051] The corresponding optical path difference is

[0052]

[0053] Where λ is the wavelength of the illumination light, and the principal stress difference within the sample layer is...

[0054]

[0055] Where C is the sample stress-strain coefficient, determined by the sample itself, and σ m,1 and σ m,2 These are the principal stresses in the two perpendicular directions at the stress point.

[0056] Compared with the prior art, the technical effects of the present invention are as follows:

[0057] 1) The device of this invention achieves three-dimensional measurement of residual stress inside a sample through a rotating dark field generator and a two-dimensional scanning system, improving the accuracy and comprehensiveness of the measurement. Using a high-definition camera to record the diffraction spot, combined with a complex iterative algorithm, high-resolution measurement results can be obtained. The entire measurement process does not require direct contact with the sample, avoiding potential errors and damage.

[0058] 2) The method of this invention utilizes high-quality dark-field recording of photoelastic information inside the glass, and then calculates the principal stress difference of the residual stress using a three-dimensional polarization stacked diffraction imaging method, thereby realizing three-dimensional measurement of stress birefringence. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the structure of the three-dimensional measuring device for residual stress inside glass according to the present invention.

[0060] In the diagram: 1-Light source, 2-Collimation system, 3-Two-dimensional scanning system, 4-Polarizer, 5-Sample to be tested, 6-Analyzer, 7-Camera. Detailed Implementation

[0061] The present invention will be further described 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.

[0062] See Figure 1 , Figure 1 This is a schematic diagram of the structure of the three-dimensional measuring device for residual stress inside glass of the present invention. As can be seen from the figure, the three-dimensional measuring device for residual stress inside glass of the present invention includes a light source 1, a collimation system 2, a two-dimensional scanning system 3, a polarizer 4, a sample to be tested 5, a polarizer 6, and a data acquisition system 7.

[0063] The illumination system consists of the light source 2 and the collimation system 2. The light source 2 is a circularly polarized light source, which illuminates the two-dimensional scanning system 3 after passing through the collimation system 2. The illumination light intensity is uniformly distributed and the aperture is larger than that of the polarizer 4.

[0064] The two-dimensional scanning system 3 is a small aperture that can move in two dimensions;

[0065] The dark field generation system consists of the polarizer 4 and the analyzer 6. The light transmission directions of the analyzer 6 and the polarizer 4 are perpendicular to each other and rotate synchronously.

[0066] The sample to be tested 5 is a transmission optical element, polished on both sides, and placed between the analyzer 6 and the polarizer 4.

[0067] The data acquisition system 7 is a high-definition camera used to record experimental data;

[0068] The method for three-dimensionally measuring the internal residual stress of glass using the aforementioned three-dimensional glass internal residual stress measuring device is characterized by the following steps:

[0069] Assuming the collimated illumination light is P0(x,y), the two-dimensional scanning system cuts the illumination light into a small-aperture beam P1(x,y). The dark-field generating device rotates continuously to three angular positions at 30° intervals. At each angular position, the two-dimensional scanning system performs one two-dimensional scan. The data acquisition system records a total of three sets of diffraction spots, denoted as P1(x,y). Ω l =0,π / 6,π / 3, l = 1, 2, 3, A, B represent the number of rows and columns in the scanning array, and there is overlap between adjacent scanning positions, with an overlap rate of approximately 70%. The sample to be tested, with a thickness of h, is placed in the dark field generation system and assumed to be M two-dimensional slices S placed along the optical axis. m (x,y), m=1:M.

[0070] 1) The transmission process of the illumination beam from the two-dimensional scanning system to the data acquisition system can be represented as:

[0071]

[0072] Where P1(x,y) represents the initially guessed complex amplitude distribution of illumination light, and H(x,y) represents the aperture function. This represents the complex amplitude distribution of the M-layer thin sample. Let represent the transmission factor of the convolution kernel in free space, z represent the transmission distance, and -z represent the distance of reverse transmission z. The distance from the two-dimensional scanning system to the front surface of the sample under test is d1, the distance from the first sample layer to the second sample layer is h1, the distance from the second sample layer to the third sample layer is h2, ..., and the distance from the rear surface of the sample under test to the data acquisition system is d2. The illumination light at the ab-th illumination position of the m-th sample layer is...

[0073] The corresponding transmitted light is Where a = 1:A and b = 1:B represent the coordinates of the diffraction spot in the two-dimensional array.

[0074] 2) Describe the light field on the surface of the data acquisition system in terms of amplitude and phase.

[0075]

[0076] The l-th set of diffraction spot arrays recorded is retrieved, and the three-dimensional reconstruction of the residual stress distribution within the sample is performed. The j-th iteration process is as follows:

[0077] 3) The diffraction spot actually recorded by the data acquisition system is used as a constraint in the iteration process, replacing the amplitude information in the update process. The updated light field distribution is as follows:

[0078]

[0079] 4) The updated light field is transmitted back to the rear surface of the sample, i.e., the transmitted light at the Mth layer of the sample is...

[0080]

[0081] 5) Update the complex amplitude distribution of the M-th layer sample using the following formula.

[0082]

[0083] 6) Update the distribution of each layer of sample in reverse order until the front surface of the sample is reached.

[0084] 7) Update the illumination distribution on the front surface of the sample.

[0085]

[0086] 8) Reverse transmission of illumination light to the position of the two-dimensional scanning system.

[0087]

[0088] Furthermore, the aperture function is incorporated as a constraint condition into the update process to promote function convergence.

[0089]

[0090] 9) Repeat steps 1-8, using the (ab+1)th diffraction spot for updating, until the sample distribution at all illumination positions is updated, and then proceed to the (j+1)th update.

[0091] 10) Obtain the photoelastic parameter distributions of each sample layer at three angles, and denote the intensity distributions as follows: The intensity distribution of the illumination light is I P Then the phase difference caused by stress birefringence on the m-th sample is:

[0092]

[0093] The corresponding optical path difference is

[0094]

[0095] Where λ is the wavelength of the illumination light, and the principal stress difference within the sample layer is...

[0096]

[0097] Where C is the sample stress-strain coefficient, determined by the sample itself, and σ m,1 and σ m,2 These are the principal stresses in the two perpendicular directions at the stress point.

[0098] In the example:

[0099] The light source 1 is a helium-neon laser, and the emitted light is circularly polarized light.

[0100] The collimation system 2 is a lens with a diameter of 75mm and a focal length of 40cm, which collimates and expands the illumination light;

[0101] The two-dimensional scanning system 3 is a small aperture with a diameter of 4mm that can move in two dimensions. It cuts the illumination beam into small-diameter illumination beams, moves 1.5mm each time, and scans a 10-row, 10-column matrix. The data acquisition system 7 records the diffraction spot at each position and obtains a set of diffraction spot arrays.

[0102] The polarizer 4 is a linear polarizer with a diameter of 50.8 mm and an extinction ratio of 10000:1;

[0103] The analyzer 6 is a linear polarizer with a diameter of 50.8 mm and an extinction ratio of 10000:1. It is perpendicular to the passing direction of the polarizer 4 and constitutes the dark field generation system.

[0104] The dark field generation system rotates π / 6 each time, for a total of 3 angular positions. The two-dimensional scanning system 3 performs a set of scans at each angular position, and the data acquisition system records a total of three sets of diffraction spots.

[0105] The sample to be tested, 5, is a calcium fluoride crystal with a diameter of 40 mm and a thickness of 12 mm.

[0106] The data acquisition system 7 is a high-definition camera with a resolution of 4096×4096, used to record experimental data;

[0107] A method for measuring residual stress inside glass, characterized by comprising the following steps:

[0108] Assuming the collimated illumination light is P0(x,y), the two-dimensional scanning system cuts the illumination light into a small-aperture beam P1(x,y). The dark-field generating device rotates continuously to three angular positions at 30° intervals. At each angular position, the two-dimensional scanning system performs one two-dimensional scan. The data acquisition system records a total of three sets of diffraction spots, denoted as P1(x,y). Ω l =0,π / 6,π / 3, l = 1, 2, 3, A, B represent the number of rows and columns in the scanning array, and there is overlap between adjacent scanning positions, with an overlap rate of approximately 70%. The sample to be tested, with a thickness of h, is placed in the dark field generation system and assumed to be M two-dimensional slices S placed along the optical axis. m (x,y), m=1:M.

[0109] 1) The transmission process of the illumination beam from the two-dimensional scanning system to the data acquisition system can be represented as:

[0110]

[0111] Where P1(x,y) represents the initially guessed complex amplitude distribution of illumination light, and H(x,y) represents the aperture function. This represents the complex amplitude distribution of the M-layer thin sample. Let represent the transmission factor of the convolution kernel in free space, z represent the transmission distance, and -z represent the distance of reverse transmission z. The distance from the two-dimensional scanning system to the front surface of the sample under test is d1, the distance from the first sample layer to the second sample layer is h1, the distance from the second sample layer to the third sample layer is h2, ..., and the distance from the rear surface of the sample under test to the data acquisition system is d2. The illumination light at the ab-th illumination position of the m-th sample layer is... The corresponding transmitted light is Where a = 1:A and b = 1:B represent the coordinates of the diffraction spot in the two-dimensional array.

[0112] 2) Describe the light field on the surface of the data acquisition system in terms of amplitude and phase.

[0113]

[0114] The l-th set of diffraction spot arrays recorded is retrieved, and the three-dimensional reconstruction of the residual stress distribution within the sample is performed. The j-th iteration process is as follows:

[0115] 3) The diffraction spot actually recorded by the data acquisition system is used as a constraint in the iteration process, replacing the amplitude information in the update process. The updated light field distribution is as follows:

[0116]

[0117] 4) The updated light field is transmitted back to the rear surface of the sample, i.e., the transmitted light at the Mth layer of the sample is...

[0118]

[0119] 5) Update the complex amplitude distribution of the M-th layer sample using the following formula.

[0120]

[0121] 6) Update the distribution of each layer of sample in reverse order until the front surface of the sample is reached.

[0122] 7) Update the illumination distribution on the front surface of the sample.

[0123]

[0124] 8) Reverse transmission of illumination light to the position of the two-dimensional scanning system.

[0125]

[0126] Furthermore, the aperture function is incorporated as a constraint condition into the update process to promote function convergence.

[0127]

[0128] 9) Repeat steps 1-8, using the (ab+1)th diffraction spot for updating, until the sample distribution at all illumination positions is updated, and then proceed to the (j+1)th update.

[0129] 10) Obtain the photoelastic parameter distributions of each sample layer at three angles, and denote the intensity distributions as follows: The intensity distribution of the illumination light is IP Then the phase difference caused by stress birefringence on the m-th sample is:

[0130]

[0131] The corresponding optical path difference is

[0132]

[0133] Where λ is the wavelength of the illumination light, and the principal stress difference within the sample layer is...

[0134]

[0135] Where C is the sample stress-strain coefficient, determined by the sample itself, and σ m,1 and σ m,2 These are the principal stresses in the two perpendicular directions at the stress point.

[0136] Experiments show that the glass internal residual stress measuring device of the present invention records three sets of diffraction spots through a rotating dark field generation system, and calculates the three-dimensional distribution of residual stress inside calcium fluoride crystals using a three-dimensional polarization stacked diffraction imaging method. The measurement accuracy of optical path difference reaches 1 nanometer, and the axial resolution is 6 millimeters. The present invention features simple device, convenient operation, and high measurement accuracy.

Claims

1. A three-dimensional measuring device for residual stress inside glass, characterized in that, include: Light source (1), used to emit circularly polarized light; A collimation system (2) is disposed after the light source (1) and is used to collimate and expand the light emitted by the light source (1); Two-dimensional scanning system (3) is used to cut the beam after collimation and expansion by the collimation system (2) into a small-aperture beam and to perform two-dimensional scanning on the surface of the sample to be tested (5); A polarizer (4) is disposed after the two-dimensional scanning system (3) for converting the small-aperture beam into linearly polarized illumination light; The analyzer (6) is located after the polarizer (4), and its light transmission direction is perpendicular to the light transmission direction of the polarizer (4), and the two rotate synchronously to form a dark field condition. The sample to be tested (5) is placed between the polarizer (4) and the analyzer (6); The data acquisition system (7) is used to acquire and record the diffraction spot images formed by the two-dimensional scanning system (3) at each scanning position when the analyzer (6) and the polarizer (4) are rotated synchronously to different rotation angles. The data processing system is connected to the data acquisition system (7) to process the diffraction spot image and reconstruct the three-dimensional residual stress distribution map inside the sample (5) under test through an iterative algorithm.

2. The three-dimensional measuring device for residual stress inside glass according to claim 1, characterized in that, It also includes a control system, which is connected to the two-dimensional scanning system (3), the polarizer (4) and the analyzer (6) respectively, to control the polarizer (4) and the analyzer (6) to rotate synchronously to form dark field conditions, and to control the two-dimensional scanning system (3) to scan once for each rotation angle.

3. The three-dimensional measuring device for residual stress inside glass according to claim 2, characterized in that, The angle is 30°.

4. The three-dimensional measuring device for residual stress inside glass according to claim 1, characterized in that, The two-dimensional scanning system is a small aperture with a diameter on the order of millimeters, which can perform two-dimensional scanning in a plane perpendicular to the direction of beam transmission.

5. The three-dimensional measuring device for residual stress inside glass according to claim 1, characterized in that, The data acquisition system is a high-definition camera.

6. The three-dimensional measuring device for residual stress inside glass according to claim 1, characterized in that, The polarizer (4) and analyzer (6) are both linear polarizers with an extinction ratio of not less than 1000:

1.

7. The three-dimensional measuring device for residual stress inside glass according to claim 1, characterized in that, The collimation system (2) is a lens.

8. A method for measuring residual stress inside glass using the three-dimensional measuring device according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1) The circularly polarized light emitted by the light source (1) is collimated by the collimation system (2) and then shines on the two-dimensional scanning system (3). The light moves in two dimensions on the surface of the sample (5) through the small hole of the two-dimensional scanning system (3) to cut out a small-diameter beam for two-dimensional scanning. Step 2) Each time, the polarizer (4) and the analyzer (6) rotate synchronously at a preset angle interval to maintain the dark field conditions; Step 3) At each rotation angle, the two-dimensional scanning system performs one two-dimensional scan, and the data acquisition system (7) records the diffraction spot image generated by the two-dimensional scanning system (3) during the scanning process; Step 4) Process the acquired diffraction spot image and use an iterative algorithm to reconstruct the three-dimensional residual stress distribution map inside the sample (5) to be tested.

9. The method for measuring residual stress inside glass according to claim 8, characterized in that, The collected diffraction spot images are processed, and the three-dimensional residual stress distribution map inside the sample (5) is reconstructed using an iterative algorithm.

10. The method for measuring residual stress inside glass according to claim 8, characterized in that, The preset angle interval is 30°, that is, π / 6 radians as the interval, and the rotation is three times.

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