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

Abstract

The invention discloses a three-dimensional measuring device and method for residual stress in glass. The three-dimensional measuring device comprises an illumination system, a two-dimensional scanning system, a dark field generation system, a sample to be measured and a data acquisition system. The illumination system consists of a light source and a collimation system and is used for providing illumination for a sample to be detected; the two-dimensional scanning system is a small hole capable of moving in two dimensions; the dark field generation system is composed of two linear polarization devices with light passing directions perpendicular to each other, and the two linear polarization devices can rotate synchronously. The sample to be detected is a transparent optical element and is arranged in the dark field generation system; the data acquisition system is used for recording experimental data; a three-dimensional polarization laminated diffraction imaging technology is developed by matching an algorithm, and the residual stress distribution in a to-be-measured element is reconstructed in a three-dimensional manner. The three-dimensional stress measurement method provided by the invention is convenient to operate and high in calculation result precision, and can meet the three-dimensional measurement of the internal residual stress of the large-aperture optical element.

Description

Technical Field

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

[0002] During the forming, annealing, cutting, polishing, coating and repairing process, residual stress will be generated in optical components, and defects will be formed inside the components. The polarized light beam passing through this will have wavefront distortion due to the birefringence effect, which will affect the beam quality and reduce the performance of the optical component. Therefore, accurate measurement of the location and size of residual stress can guide the improvement of material growth technology and component repair technology, and predict the direction of defects inside optical materials. In addition, observing the birefringence characteristics of biological metabolites can also be used for disease diagnosis and cancer cell screening.

[0003] In general, stress changes along the optical path, so three-dimensional photoelastic data is required to finely reconstruct the internal structural information of the sample. At present, there are some three-dimensional measurement technologies, including finite element method, frozen stress slicing method, corrosion method, integrated photoelastic method, tomography method, Fourier method, etc. Among them, the finite element method cannot obtain experimental parameters that are completely consistent with the actual situation and can only be used as a reference for the actual operation process. Frozen stress slicing method and corrosion method will cause irreversible damage to the material, so they are rarely used in the measurement of large optical components and living samples. The integrated photoelastic method requires the three-dimensional photoelastic model to be equivalent to an optical model containing a linear phase retarder and an optical rotator, and the theoretical analysis is relatively complicated. The tomography method has high imaging accuracy, but the relative position of the sample and the detection light needs to be changed many times during the measurement process, the amount of data is large, and the reconstruction process is complicated. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and propose a three-dimensional measurement device and method for residual stress inside glass. The photoelastic information inside the glass is obtained by using a high-quality dark field, and the distribution of parameters such as the three-dimensional phase difference, optical path difference, and principal stress difference in the sample is calculated by combining the three-dimensional polarization stacked diffraction imaging technology proposed by the present invention. The measurement device and measurement method can be applied to the three-dimensional measurement of stress birefringence. The dark field distribution at three angles is recorded by scanning, and the photoelastic information at each angle is first reconstructed in layers. Then, the stress distribution inside the optical element is reconstructed in three dimensions by the phase shift method to obtain the axial position of the stress inside 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 the one hand, the present invention provides a three-dimensional measurement device for residual stress inside glass, which is characterized in that it includes:

[0007] a light source for emitting circularly polarized light;

[0008] A collimation system, arranged after the light source, for collimating and expanding the light emitted by the light source;

[0009] A two-dimensional scanning system, used for cutting the light beam collimated and expanded by the collimation system into a small-caliber light beam, and performing a two-dimensional scan on the surface of the sample to be tested;

[0010] A polarizer, disposed after the two-dimensional scanning system, for converting the light beam into illumination light of a specific polarization state;

[0011] An analyzer is arranged after the polarizer and is perpendicular to the light transmission direction of the polarizer, and the two rotate synchronously to form a dark field condition;

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

[0013] A data acquisition system, used to collect and record diffraction spot images at different rotation angles and scanning positions;

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

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

[0016] Preferably, the angle is 30°.

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

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

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

[0020] Preferably, the collimating 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 three-dimensional measuring device, which is 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 irradiated on the two-dimensional scanning system. The small hole of the two-dimensional scanning system moves two-dimensionally on the surface of the sample to be tested, and a small-aperture light beam is cut out for two-dimensional scanning;

[0023] Step 2) each time the polarizer and the analyzer are synchronously rotated at a preset angle interval to maintain a dark field condition;

[0024] Step 3) at each rotation angle, the two-dimensional scanning system performs a 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 collected diffraction spot image and reconstruct the three-dimensional residual stress distribution map inside the sample to be tested using an iterative algorithm.

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

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

[0028] Assume that the collimated illumination light is P 0 (x, y), the two-dimensional scanning system cuts the illumination light into a small-diameter beam P 1 (x, y), the dark field generating device rotates continuously to three angle positions at intervals of 30°. At each angle position, the two-dimensional scanning system performs a two-dimensional scan, and the data acquisition system records a total of three groups of diffraction spots, which are recorded as Ω l =0,π / 6,π / 3, l=1,2,3, A, B represent the number of rows and columns in the scanning array, there is overlap between adjacent scanning positions, and the overlap rate is about 70%. The sample to be tested with a thickness of h is placed in the dark field generation system and is 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 expressed as:

[0030]

[0031] Among them, P 1 (x, y) represents the initial guess of the illumination light complex amplitude distribution, H(x, y) represents the aperture function, represents the complex amplitude distribution of M-layer thin samples, represents the transmission factor of the convolution kernel in free space, z represents the transmission distance, -z represents the distance of the reverse transmission z, wherein the distance from the two-dimensional scanning system to the front surface of the sample to be tested is d 1 , the distance from the first layer of samples to the second layer of samples is h 1 , the distance from the second layer sample to the third layer sample is h 2 , ..., the distance from the rear surface of the sample to be tested to the data acquisition system is d 2 The illumination light at the abth illumination position of the mth layer sample is The corresponding transmitted light is Where a=1:A, b=1:B, representing the coordinates of the diffraction spot in the two-dimensional array.

[0032] 2) Write the light field on the surface of the data acquisition system in the form of amplitude and phase

[0033]

[0034] Take out the recorded l-th group of diffraction spot arrays and reconstruct the residual stress distribution in the sample in three dimensions. The j-th iteration process is as follows:

[0035] 3) The diffraction spots actually recorded by the data acquisition system are brought into the iteration process as constraints, replacing the amplitude information in the update process. The updated light field distribution is

[0036]

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

[0038]

[0039] 5) Update the complex amplitude distribution of the Mth layer samples using the following formula:

[0040]

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

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

[0043]

[0044] 8) Reversely transmit the illumination light to the position of the two-dimensional scanning system

[0045]

[0046] And the hole function is brought into the update process as a constraint to promote function convergence

[0047]

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

[0049] 10) The photoelastic parameter distribution of each layer of samples at three angles is obtained, and the intensity distribution is recorded as The intensity distribution of the illumination light is I P , then the phase difference caused by stress birefringence on the mth layer of the 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 in the layer of the sample is

[0054]

[0055] Where C is the stress strain coefficient of the sample, which is determined by the sample itself, σ m,1 and σ m,2 are the principal stresses in 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 the present invention realizes three-dimensional measurement of residual stress inside the sample through a rotating dark field generating device and a two-dimensional scanning system, thereby 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 to be measured, thus avoiding possible errors and damage.

[0058] 2) The method of the present invention uses high-quality dark field to record the photoelastic information inside the glass, and then calculates the principal stress difference of the residual stress by the three-dimensional polarization stack diffraction imaging method to achieve three-dimensional measurement of stress birefringence BRIEF DESCRIPTION OF THE DRAWINGS

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

[0060] In the figure: 1-light source, 2-collimation system, 3-two-dimensional scanning system, 4-polarizer, 5-sample to be tested, 6-analyzer, 7-camera. DETAILED DESCRIPTION

[0061] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereto.

[0062] See also Figure 1 , Figure 1 It is a structural schematic diagram 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 measured 5, an analyzer 6, and a data acquisition system 7.

[0063] The illumination system is composed of the light source 2 and the collimation system 2. The light source 2 is a circularly polarized light source, which is irradiated onto the two-dimensional scanning system 3 after passing through the collimation system 2. The illumination light intensity is evenly distributed and has a larger aperture than the polarizer 4.

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

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

[0066] The sample 5 to be tested is a transmission optical element, polished on both sides, and is 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 above-mentioned three-dimensional measuring device for internal residual stress of glass is characterized in that the measuring method comprises the following steps:

[0069] Assume that the collimated illumination light is P 0 (x, y), the two-dimensional scanning system cuts the illumination light into a small-diameter beam P 1 (x, y), the dark field generating device rotates continuously to three angle positions at intervals of 30°. At each angle position, the two-dimensional scanning system performs a two-dimensional scan, and the data acquisition system records a total of three groups of diffraction spots, which are recorded as Ω l =0,π / 6,π / 3, l=1,2,3, A, B represent the number of rows and columns in the scanning array, there is overlap between adjacent scanning positions, and the overlap rate is about 70%. The sample to be tested with a thickness of h is placed in the dark field generation system and is 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 expressed as:

[0071]

[0072] Among them, P 1 (x, y) represents the initial guess of the illumination light complex amplitude distribution, H(x, y) represents the aperture function, represents the complex amplitude distribution of M-layer thin samples, represents the transmission factor of the convolution kernel in free space, z represents the transmission distance, -z represents the distance of the reverse transmission z, wherein the distance from the two-dimensional scanning system to the front surface of the sample to be tested is d 1 , the distance from the first layer of samples to the second layer of samples is h 1 , the distance from the second layer sample to the third layer sample is h 2 , ..., the distance from the rear surface of the sample to be tested to the data acquisition system is d 2 The illumination light at the abth illumination position of the mth layer sample is

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

[0074] 2) Write the light field on the surface of the data acquisition system in the form of amplitude and phase

[0075]

[0076] Take out the recorded l-th group of diffraction spot arrays and reconstruct the residual stress distribution in the sample in three dimensions. The j-th iteration process is as follows:

[0077] 3) The diffraction spots actually recorded by the data acquisition system are brought into the iteration process as constraints, replacing the amplitude information in the update process. The updated light field distribution is

[0078]

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

[0080]

[0081] 5) Update the complex amplitude distribution of the Mth layer samples using the following formula:

[0082]

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

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

[0085]

[0086] 8) Reversely transmit the illumination light to the position of the two-dimensional scanning system

[0087]

[0088] And the hole function is brought into the update process as a constraint to promote function convergence

[0089]

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

[0091] 10) The photoelastic parameter distribution of each layer of samples at three angles is obtained, and the intensity distribution is recorded as The intensity distribution of the illumination light is I P , then the phase difference caused by stress birefringence on the mth layer of the 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 in the layer of the sample is

[0096]

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

[0098] In the embodiment:

[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 75 mm and a focal length of 40 cm, which collimates and expands the illumination light;

[0101] The two-dimensional scanning system 3 is a small hole that can move in two dimensions, with a diameter of 4 mm, which cuts the illumination beam into small-caliber illumination lights, moves 1.5 mm each time, and scans a matrix of 10 rows and 10 columns. The data acquisition system 7 records the diffraction spot at each position to obtain 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, which 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, and rotates to 3 angle positions in total. The two-dimensional scanning system 3 performs a set of scans at each angle position, and the data acquisition system records a total of three sets of diffraction spots;

[0105] The sample 5 to be tested 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, which is used to record experimental data;

[0107] The method for measuring the residual stress inside the glass is characterized in that the measuring method comprises the following steps:

[0108] Assume that the collimated illumination light is P 0 (x, y), the two-dimensional scanning system cuts the illumination light into a small-diameter beam P 1 (x, y), the dark field generating device rotates continuously to three angle positions at intervals of 30°. At each angle position, the two-dimensional scanning system performs a two-dimensional scan, and the data acquisition system records a total of three groups of diffraction spots, which are recorded as Ω l =0,π / 6,π / 3, l=1,2,3, A, B represent the number of rows and columns in the scanning array, there is overlap between adjacent scanning positions, and the overlap rate is about 70%. The sample to be tested with a thickness of h is placed in the dark field generation system and is 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 expressed as:

[0110]

[0111] Among them, P 1(x, y) represents the initial guess of the illumination light complex amplitude distribution, H(x, y) represents the aperture function, represents the complex amplitude distribution of M-layer thin samples, represents the transmission factor of the convolution kernel in free space, z represents the transmission distance, -z represents the distance of the reverse transmission z, wherein the distance from the two-dimensional scanning system to the front surface of the sample to be tested is d 1 , the distance from the first layer of samples to the second layer of samples is h 1 , the distance from the second layer sample to the third layer sample is h 2 , ..., the distance from the rear surface of the sample to be tested to the data acquisition system is d 2 The illumination light at the abth illumination position of the mth layer sample is The corresponding transmitted light is Where a=1:A, b=1:B, representing the coordinates of the diffraction spot in the two-dimensional array.

[0112] 2) Write the light field on the surface of the data acquisition system in the form of amplitude and phase

[0113]

[0114] Take out the recorded l-th group of diffraction spot arrays and reconstruct the residual stress distribution in the sample in three dimensions. The j-th iteration process is as follows:

[0115] 3) The diffraction spots actually recorded by the data acquisition system are brought into the iteration process as constraints, replacing the amplitude information in the update process. The updated light field distribution is

[0116]

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

[0118]

[0119] 5) Update the complex amplitude distribution of the Mth layer samples using the following formula:

[0120]

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

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

[0123]

[0124] 8) Reversely transmit the illumination light to the position of the two-dimensional scanning system

[0125]

[0126] And the hole function is brought into the update process as a constraint to promote function convergence

[0127]

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

[0129] 10) The photoelastic parameter distribution of each layer of samples at three angles is obtained, and the intensity distribution is recorded as The intensity distribution of the illumination light is I P , then the phase difference caused by stress birefringence on the mth layer of the 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 in the layer of the sample is

[0134]

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

[0136] Experiments show that the glass internal residual stress measuring device of the present invention records three groups of diffraction spots through a rotating dark field generation system, and uses a three-dimensional polarization stacked diffraction imaging method for calculation, so as to obtain the three-dimensional distribution of residual stress inside the calcium fluoride crystal, and the measurement accuracy of the optical path difference reaches 1 nanometer, and the axial resolution is 6 millimeters. The present invention has the characteristics of simple device, convenient operation and high measurement accuracy.

Claims

1. A three-dimensional measurement device for residual stress inside glass, characterized in that: include: A light source (1) for emitting circularly polarized light; A collimation system (2), arranged after the light source (1), for collimating and expanding the light emitted by the light source (1); A two-dimensional scanning system (3) is used to cut the light beam collimated and expanded by the collimation system (2) into a small-aperture light beam, and to perform two-dimensional scanning on the surface of the sample to be measured (5); A polarizer (4), arranged after the two-dimensional scanning system (3), used for converting the light beam into illumination light of a specific polarization state; An analyzer (6) is arranged behind the polarizer (4) and 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); A data acquisition system (7), used for collecting and recording diffraction spot images at different rotation angles and scanning positions; The data processing system is connected to the data acquisition system (7), processes the diffraction spot image, and reconstructs a three-dimensional residual stress distribution map inside the sample to be tested (5) through an iterative algorithm.

2. The three-dimensional measurement device for residual stress inside glass according to claim 1, characterized in that: The invention also comprises a control system, which is respectively connected to the two-dimensional scanning system (3), the polarizer (4) and the analyzer (6), and is used to control the polarizer (4) and the analyzer (6) to rotate synchronously to form a dark field condition, and to control the two-dimensional scanning system (3) to scan once every 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 measurement device for residual stress inside glass according to claim 1, characterized in that: The two-dimensional scanning system is a small hole with a diameter of the order of millimeters, which can perform two-dimensional scanning in a plane perpendicular to the transmission direction of the light beam.

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

1.

7. The three-dimensional measurement device for residual stress inside glass according to claim 1, characterized in that: The collimating 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 to 7, characterized in that: The steps include: Step 1) The circularly polarized light emitted by the light source (1) is collimated by the collimation system (2) and then irradiated onto the two-dimensional scanning system (3). The light moves two-dimensionally on the surface of the sample to be tested (5) through the small hole of the two-dimensional scanning system (3), and a small-aperture light beam is cut out for two-dimensional scanning; Step 2) each time the polarizer (4) and the analyzer (6) rotate synchronously at a preset angle interval to maintain a dark field condition; Step 3) at each rotation angle, the two-dimensional scanning system performs a two-dimensional scan, and the data acquisition system (7) records the diffraction spot image generated during the scanning process of the two-dimensional scanning system (3); Step 4) The collected diffraction spot image is processed and an iterative algorithm is used to reconstruct a three-dimensional residual stress distribution map inside the sample to be tested (5).

9. The method for measuring residual stress inside glass according to claim 8, characterized in that: The collected diffraction spot image is processed, and an iterative algorithm is used to reconstruct a three-dimensional residual stress distribution map inside the sample to be tested (5).

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 is the interval, and the rotation is three times.

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