A device and method for measuring internal stress based on PBS spectrometer

Abstract

The application provides a kind of internal stress measuring device and measuring method based on PBS spectrometer, including polarization spectrometer system, sample table, 1 / 4 wave plate, analyzer, image pickup element and image processing unit arranged in turn along the direction of light path, polarization spectrometer system includes first light source and second light source, first collimating mirror and second collimating mirror, first PBS spectrometer prism and second PBS spectrometer prism, first light shield group and second light shield group, mirror group, multiple light combiner prism.Polarization spectrometer system controls the opening and closing state of first light shield group and second light shield group, and outputs 0°, 45°, 90°, 135° four angle polarized light at the end light combiner.The application not only solves the problem of speed and reliability through motionless component design, but also overcomes the fatal weakness of traditional scheme, such as large temperature influence and dependence on import, and provides a kind of high performance, high stability, high cost-effective internal stress measurement solution, which effectively promotes the localization process of high-end industrial detection equipment.

Description

Technical Field

[0001] This invention relates to the field of detection, and more particularly to an internal stress measurement device and method based on PBS spectroscopy. Background Technology

[0002] In fields such as optical manufacturing, glass processing, aerospace, and quality inspection of transparent materials, the accurate and rapid detection of residual stress within materials is of paramount importance. Residual stress affects the mechanical properties, optical properties, and long-term stability of materials, thus necessitating a reliable quantitative detection method.

[0003] Currently, polarization measurement based on the photoelastic effect is the mainstream nondestructive testing method. However, current measurement systems typically have the following significant limitations: The core components are heavily reliant on imports, which severely restricts their use: Most measurement systems use thin-film polymer polarizers as the core polarization element. High-performance polarizer materials are mostly monopolized by foreign manufacturers, which not only result in high prices but also pose supply chain risks and technological limitations, severely hindering the independent development and cost control of domestically produced high-end testing equipment.

[0004] Poor reliability and susceptibility to environmental influences: The aforementioned thin-film polarizer has a sheet-like polymer structure, and its physical properties are highly sensitive to temperature changes. Under fluctuating ambient temperatures or prolonged exposure to light sources, it is prone to deformation and warping, causing a drift in its polarization axis direction, which directly introduces measurement errors and severely affects the accuracy of the results.

[0005] Insufficient dynamic performance: To achieve multi-angle measurement, existing solutions typically use mechanically rotating waveplates or polarizers to switch polarization angles. This mechanical motion suffers from problems such as slow speed, wear, short lifespan, and susceptibility to vibration interference, making it difficult to meet the high throughput and high reliability requirements of industrial online inspection. Summary of the Invention

[0006] In view of the above, the present invention provides an internal stress measurement device and method based on PBS spectroscopy. The present invention not only solves the problems of speed and reliability through the design of no moving parts, but also overcomes the fatal weaknesses of traditional solutions, such as being greatly affected by temperature and relying on imports, by replacing the thin film polarizer with a PBS prism, a core material innovation. It provides a high-performance, high-stability, and cost-effective internal stress measurement solution, which powerfully promotes the localization process of high-end industrial testing equipment.

[0007] The present invention specifically adopts the following technical solution: an internal stress measurement device based on PBS spectroscopy, comprising a polarization spectroscopy system, a sample stage, a quarter-wave plate, an analyzer, an imaging element, and an image processing unit arranged sequentially along the optical path, wherein the polarization spectroscopy system includes... The first and second light sources are used to emit monochromatic light; The first collimating lens and the second collimating lens are respectively disposed in the output light paths of the first light source and the second light source, and are used to collimate the light beam; The first PBS beam splitter and the second PBS beam splitter receive collimated light from the first collimating lens and the second collimating lens, respectively. The first PBS beam splitter transmits 0° linearly polarized light and reflects 90° linearly polarized light, while the second PBS beam splitter transmits 45° linearly polarized light and reflects 135° linearly polarized light. The first and second light-shielding plate groups are respectively disposed on the output optical paths of the first and second PBS beam splitters and are used to selectively switch the optical paths on and off. A set of mirrors is used to refract light polarized at 0°, 90°, and 135°. Multiple light-combining prisms, each including a first light-combining prism, a second light-combining prism, and a third light-combining prism, wherein the first light-combining prism is located on the output optical path of the first light-shielding plate group, the second light-combining prism is located on the output optical path of the second light-shielding plate group, and the third light-combining prism is positioned to simultaneously receive the outgoing light from the first light-combining prism and the outgoing light from the second light-combining prism, and combines the two light paths for output; The polarization beam splitting system controls the opening and closing states of the first and second light-shielding plate groups to output four-angle polarized light at the third beam combining prism: 0°, 45°, 90°, and 135°.

[0008] As a further improved technical solution, the first PBS beam splitter and the second PBS beam splitter have the same structure, and the second PBS beam splitter is installed with the optical axis rotated 45° relative to the first PBS beam splitter.

[0009] As a further improved technical solution, the first, second, and third beam combining prisms have the same structure, each including four right-angle prism surfaces a, b, c, and d. Surfaces a and c are coated with a film layer that reflects S-polarized light and is used to reflect 0° and 90° polarized light, while surfaces b and d are coated with a film layer that transmits P-polarized light and is used to transmit 45° and 135° polarized light.

[0010] As a further improved technical solution, the first light-shielding plate group includes a first light-shielding plate and a second light-shielding plate, the first light-shielding plate controls the on / off of a 90° polarized light path, and the second light-shielding plate controls the on / off of a 0° polarized light path; the second light-shielding plate group includes a third light-shielding plate and a fourth light-shielding plate, the third light-shielding plate controls the on / off of a 135° polarized light path, and the fourth light-shielding plate controls the on / off of a 45° polarized light path.

[0011] As a further improved technical solution, the first, second, third, and fourth light-shielding plates are each driven by a motor, thereby independently controlling the on / off state of polarized light at each angle.

[0012] As a further improved technical solution, the reflector group includes a first reflector, a second reflector, a third reflector, a fourth reflector, and a fifth reflector. The first and second reflectors are located on the output optical path of the first light-shielding plate, the fourth and fifth reflectors are located on the output optical path of the third light-shielding plate, and the third reflector is located on the output optical path of the first beam combining prism, for receiving and refracting the light beam from the first beam combining prism.

[0013] As a further improved technical solution, the first, second, third, fourth and fifth reflectors are each coated with a silver film or an aluminum film.

[0014] As a further improved technical solution, the third reflecting mirror is located on the output optical path of the first light combining prism and on the input optical path of the third light combining prism. The light reflected by the third reflecting mirror and the light output by the second light combining prism are both input to the third light combining prism.

[0015] An internal stress measurement method based on PBS spectroscopy is disclosed. The internal stress measurement device described above is used to detect the sample under test. By switching the opening and closing states of the first and second light-shielding plate groups, four-angle polarized light of 0°, 45°, 90°, and 135° is generated at the third light-combining prism and passes through the sample under test, the quarter-wave plate, and the analyzer in sequence. The imaging element acquires four sets of interference images and transmits them to the image processing unit. The image processing unit calculates the stress value by background subtraction and brightness analysis.

[0016] As a further improved technical solution, the image processing unit performs the following steps: when there is no sample to be tested, it sequentially acquires background images of four-angle polarized light; after placing the sample, it sequentially acquires sample images of four-angle polarized light; after deducting background noise, it calculates the birefringence optical path difference based on the brightness difference and inverts the stress distribution.

[0017] This invention relates to an internal stress measurement device and method based on PBS spectroscopy. It innovatively introduces the PBS cube, commonly used in the communication / laser field, into the glass internal stress measurement scenario as the core polarization and spectroscopy element. It replaces "mechanical rotation" with "static optical path + electronic switching", opening up a completely new technical route that does not require any rotating waveplates or thin films. There are no rotating parts in the optical path, and all polarization directions are determined by the fixed PBS and the reflector. The light shield is only responsible for "on / off", without introducing angular errors, and has good repeatability. By utilizing PBS beam splitting and quadrature prism beam combining, high-speed switching and beam combining of four-directional linearly polarized light (0° / 45° / 90° / 135°) is achieved, realizing "single-port output and four-axis scanning," thus improving detection efficiency. The electric light shield switching speed reaches the millisecond level. Combined with the dual-optical-path design, the time to fully acquire data at four polarization angles is greatly shortened, meeting the cycle time of high-speed production lines. Moreover, the glass PBS prism has an extremely low coefficient of thermal expansion, and its physical form and optical performance remain highly stable within an ambient temperature range of -20℃ to 80℃. This fundamentally solves the problem of polarization axis drift caused by heat warping and deformation of polymer film polarizers, ensuring the long-term accuracy and reliability of measurement data. At the same time, the PBS prism can be manufactured using domestically produced optical glass and coating technology, breaking the foreign material monopoly, ensuring a secure and controllable supply chain, reducing costs, and making the overall machine more competitive in terms of cost. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the internal stress measurement device based on PBS spectroscopy in this application.

[0019] Figure 2 This is a schematic diagram of the optical path distribution of the polarization beam splitting system of this application. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] Reference Figure 1An internal stress measurement device based on PBS (Polarization-Based Beam Spectroscopy) includes a polarization beam splitting system 1, a sample stage 2, a quarter-wave plate 3, an analyzer 4, an image acquisition element 5, and an image processing unit arranged sequentially along the optical path. The polarization beam splitting system 1 outputs four-angle polarized light. The sample stage 2 holds the sample 6 to be measured. The quarter-wave plate 3 converts the polarized light transmitted through the sample into circularly polarized light. The analyzer 4 generates an interference image related to the stress distribution of the sample; a Glan-Taylor prism is optional. The image acquisition element 5 captures the interference image; a CCD camera or a CMOS camera is optional. The image processing unit is electrically connected to the image acquisition element 5 and calculates the internal stress of the sample based on the brightness information of the four-angle polarized light image. An industrial PC (IPC) or embedded processor with a high-performance CPU / GPU is used to quickly perform a large amount of image processing and matrix operations. A high-speed image acquisition card receives signals from the image acquisition element 5. High-speed image data stream ensures no data loss and low latency; multi-channel I / O control card controls the motor of the light shield, receives software commands, and sends "on / off" signals to achieve automatic switching of polarized light on / off; communication interfaces, such as gigabit Ethernet and USB 3.0, are used to communicate with the camera and host computer.

[0023] Specific references Figure 2 The polarization beam splitting system 1 includes a first light source 110, a second light source 120, a first collimating lens 111, a second collimating lens 121, a first PBS beam splitting prism 112, a second PBS beam splitting prism 122, a first light-shielding plate group, a second light-shielding plate group, a reflector group, and multiple beam combining prisms. By controlling the opening and closing states of the first and second light-shielding plate groups, the polarization beam splitting system 1 outputs four-angle polarized light at 0°, 45°, 90°, and 135° at the final beam combining prism.

[0024] Furthermore, the first light source 110 and the second light source 120 are used to emit monochromatic light. They can be LEDs with a wavelength of 560nm or other wavelengths. They are installed with their optical axes parallel within the polarization beam splitting system 1, with a parallelism error of less than 0.5°, to ensure that the two beams can be accurately combined at the beam combining prism and avoid measurement errors. The first collimating lens 111 and the second collimating lens 121 are respectively disposed on the output light paths of the first light source 110 and the second light source 120 to collimate the beams. The first PBS beam splitter prism 112 and the second PBS beam splitter prism 122 receive collimated light from the first collimating lens 111 and the second collimating lens 121, respectively. The first PBS beam splitter prism 112 and the second PBS beam splitter prism 122 are identical cubic prisms of the same specifications, composed of two right-angle prisms with a dielectric beam-splitting film coated on their inclined surfaces. The second PBS beam splitter prism 122 is installed with its incident light axis rotated 45° relative to the first PBS beam splitter prism 112. That is, during installation, their incident surfaces are parallel and their incident light axes are coaxial. The second PBS beam splitter prism 122 is then rotated 45° around its incident light axis and fixed, so that its beam splitting direction forms a 45° angle with the beam splitting direction of the first PBS beam splitter prism 112. The first PBS beam splitter prism 112 transmits 0° linearly polarized light and reflects 90° linearly polarized light, while the second PBS beam splitter prism 122 transmits 45° linearly polarized light and reflects 135° linearly polarized light. The first and second light-shielding plate groups are respectively disposed on the output optical paths of the first PBS beam splitter 112 and the second PBS beam splitter 122 for selectively switching on and off the optical paths. The first light-shielding plate group includes a first light-shielding plate 113 and a second light-shielding plate 114. The first light-shielding plate 113 controls the switching on and off of the 90° polarized optical path, that is, the first light-shielding plate 113 is located on the output optical path of the first PBS beam splitter reflecting 90° linearly polarized light. The second light-shielding plate 114 controls the switching on and off of the 0° polarized optical path, that is, the second light-shielding plate 114 is located on the output optical path of the first PBS beam splitter 112 transmitting 0° linearly polarized light. The first light-shielding plate 113 and the second light-shielding plate 114 cannot be opened simultaneously. The second light-shielding plate group includes a third light-shielding plate 123 and a fourth light-shielding plate 124. The third light-shielding plate 123 controls the on / off state of the 135° polarized light path, meaning that the third light-shielding plate 123 is located on the output light path of the second PBS beam splitter 122 reflecting 135° linearly polarized light. The fourth light-shielding plate 124 controls the on / off state of the 45° polarized light path, meaning that the fourth light-shielding plate 124 is located on the output light path of the second PBS beam splitter 122 transmitting 45° linearly polarized light. The third light-shielding plate 123 and the fourth light-shielding plate 124 cannot be activated simultaneously. The first light-shielding plate 113, the second light-shielding plate 114, the third light-shielding plate 123, and the fourth light-shielding plate 124 are each driven by a motor, thereby independently controlling the on / off state of the polarized light at each angle.

[0025] The reflector group, used to refract 0°, 90°, and 135° polarized light, specifically includes a first reflector 115, a second reflector 116, a third reflector 118, a fourth reflector 125, and a fifth reflector 126. The first and second reflectors 115 and 116 are located on the output light path of the first light-shielding plate 113, and the fourth and fifth reflectors 125 and 126 are located on the output light path of the third light-shielding plate 123. The third reflector 118 is positioned on the final beam combining path of the 0° and 90° polarized light generated by the first light source 110, i.e., the output light path of the first beam combining prism 117, and is used to receive the beam from the first beam combining prism 117 and refract it towards the final beam combining prism, i.e., the third beam combining prism 130. Each of the first, second, and fifth reflectors 115, 116, 118, 125, and 126 is coated with a silver or aluminum film, with a reflectivity >98%.

[0026] The multiple beam combining prisms include a first beam combining prism 117, a second beam combining prism 127, and a third beam combining prism 130. The first beam combining prism 117 is located on the output optical path of the first light shielding plate group. That is, the optical path of the 90° linearly polarized light reflected by the first PBS beam splitter prism 112 after being reflected by the first reflector 115 and the second reflector 116, and the 0° linearly polarized light transmitted by the first PBS beam splitter prism 112 are both input into the first beam combining prism 117, and then output through different interfaces of the first beam combining prism 117 before entering the third reflector 118. The second beam combining prism 127 is located on the output optical path of the second light shielding plate group. That is, the optical path of the 135° linearly polarized light reflected by the second PBS beam splitter prism 122 after being reflected by the fourth mirror 125 and the fifth mirror 126, and the 45° linearly polarized light transmitted by the second PBS beam splitter prism 122 are both input into the second beam combining prism 127, and then output through different interfaces of the second beam combining prism 127 before entering the third beam combining prism 130. The third beam combiner 130 is positioned to simultaneously receive the outgoing light from the first beam combiner 117 and the outgoing light from the second beam combiner 127, and combines the two beams for output. Furthermore, the third reflector 118 is located on the output beam path of the first beam combiner 117 and on the input beam path of the third beam combiner 130, changing the direction of the beam output from the first beam combiner 117 and directing it into the third beam combiner 130 for output. The light reflected by the third reflector 118 and the light output from the second beam combiner 127 are both input into the third beam combiner 130. The first light shield 113, the second light shield 114, the third light shield 123, and the fourth light shield 124 are opened to allow polarized light to pass through, and the third beam combiner 130 outputs polarized light at four angles of 0°, 45°, 90°, and 135° in a time-division manner.

[0027] The first beam combining prism 117, the second beam combining prism 127, and the third beam combining prism 130 have the same structure, each consisting of four right-angle prisms. The right-angle sides of the right-angle prisms are coated with a reflective film and a transmittance film for polarized light. Each beam combining prism includes four right-angle prism surfaces a, b, c, and d. Surfaces a and c are coated with a film layer that reflects S-polarized light and is used to reflect 0° and 90° polarized light. Surfaces b and d are coated with a film layer that transmits P-polarized light and is used to transmit 45° and 135° polarized light.

[0028] The following is a table showing the switching status of the light-shielding panel: Target output polarized light First sunshade (90°) Second sunshade (0°) Third sunshade (135°) Fourth sunshade (45°) 0° close open close close 90° open close close close 45° close close close open 135° close close open close .

[0029] A method for measuring internal stress based on PBS spectroscopy is described above. The internal stress measuring device is used to detect the sample 6 under test. By switching the opening and closing states of the first and second light-shielding plate groups, four-angle polarized light of 0°, 45°, 90° and 135° is generated at the third beam combining prism 130 and passed through the sample 6 under test, the quarter-wave plate 3 and the analyzer 4 in sequence. The imaging element 5 collects four sets of interference images and transmits them to the image processing unit. The image processing unit calculates the stress value by background subtraction and brightness analysis.

[0030] When there is no sample 6 to be tested, the image processing unit sequentially acquires the background image of the four-angle polarized light. After the sample is placed, it sequentially acquires the sample image of the four-angle polarized light. Then, the background noise is subtracted, the birefringence optical path difference is calculated based on the brightness difference, and the stress distribution is inverted.

[0031] The internal stress measurement process is as follows: The measuring device is calibrated before its first use to obtain the inherent noise and background image of the system itself, which is then subtracted from the sample image to ensure the accuracy of the measurement data. The image processing unit selects the polarization angle to be calibrated through the internal software interface and sends a clear instruction to the light-shielding plate driving circuit. For example, to prepare to output 0° polarized light, the first light-shielding plate 113, the third light-shielding plate 123, and the fourth light-shielding plate 124 are closed under the drive of the motor, and the second light-shielding plate 114 is opened under the drive of the motor. At this time, only the optical path of 0° polarized light is unobstructed. The optical path is as follows: first light source 110 → first collimating lens 111 → first PBS beam splitter prism 112 (0°P light transmission) → open second light-shielding plate 114 → first beam combiner prism 117 (transmission) → third reflecting mirror 118 → third beam combiner prism 130 → output 0° polarized light. This 0° polarized light passes sequentially through the empty sample stage 2, 1 / 4 wave plate 3, and analyzer 4. After the optical path is stabilized, the imaging element 5 is exposed to acquire a background image and stores it as I_bg(0°). This image includes all non-sample factors such as system dust, uneven illumination, and optical device defects. In a cyclic switching manner, just like acquiring I_bg(0°), the image processing unit sends instructions in sequence to switch the light-shielding plate group to the states of 45°, 90°, and 135°, and acquires and stores I_bg(45°), I_bg(90°), and I_bg(135°) respectively.

[0032] For formal sample measurement, the sample to be tested 6 is placed on the sample stage 2. The image processing unit completely repeats the steps of the background calibration, controlling the light shield to switch the four angles in the same order. The action logic of the light shield is consistent with that of the background calibration. The key change occurs after the light passes through the sample. When linearly polarized light passes through a stressed sample, the birefringence effect inside the sample will decompose the beam into two beams of light with perpendicular vibration directions and different propagation speeds (o-light and e-light), thereby producing a phase delay (optical path difference δ) and changing the polarization state of the outgoing light, usually turning it into elliptically polarized light. A quarter-wave plate converts elliptically polarized light into linearly polarized light, but its polarization direction is rotated relative to the incident light. The analyzer only allows light vibrations in specific directions to pass through, and its transmitted light intensity contains phase delay information caused by the sample. The greater the stress, the greater the optical path difference, which leads to a change in the final transmitted light intensity. The camera acquires images modulated by the sample at four angles and stores them as I_sample(0°), I_sample(45°), I_sample(90°), and I_sample(135°). The software in the image processing unit then automatically calculates I_final(θ) = I_sample(θ) - I_bg(θ) (θ = 0°, 45°, 90°, 135°) to obtain the intensity change caused purely by the sample.

[0033] For each pixel coordinate (x, y) in the image, the software reads the net intensity values ​​I0, I1, ..., I2 of the image at the four polarization angles. 45 , I 90 , I 135 Where I0 = I_final(0°) is the pixel value at point (x,y), and I 45 =I_final(45°) is the pixel value at point (x,y), I 90 =I_final(90°) represents the pixel value at point (x,y), I 135 =I_final(135°) is the pixel value at point (x,y). Substituting this into the calculation of the phase difference φ, a four-step phase shift method is used. φ = atan2((I 135 -I 45 ), (I0- I 90 `atan2` is the four-quadrant arctangent function, which can provide accurate values ​​in the range of 0-2π. Calculate the optical path difference δ: δ=(φ*λ) / (2π), where λ is the wavelength of the light source, for example, 560nm. According to the stress optics law, calculate the stress σ=δ / (C * d), where C is the stress optics constant of the material (selectable from the user menu), and d is the sample thickness (manually input or automatically read by a laser thickness gauge). Finally, the software generates a stress distribution cloud map. The color of each pixel in the map represents the stress magnitude at that point, and quantitative values ​​can be output; for example, blue represents low-pressure stress, and red represents high-pressure stress.

[0034] Furthermore, the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. The understanding of this specification should be based on those skilled in the art. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still make modifications or equivalent substitutions to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. An internal stress measurement device based on PBS spectroscopy, characterized in that: The system includes a polarization beam splitting system, a sample stage, a quarter-wave plate, an analyzer, an image acquisition element, and an image processing unit, arranged sequentially along the optical path. The polarization beam splitting system includes... The first and second light sources are used to emit monochromatic light; The first collimating lens and the second collimating lens are respectively disposed in the output light paths of the first light source and the second light source, and are used to collimate the light beam; The first PBS beam splitter and the second PBS beam splitter receive collimated light from the first collimating lens and the second collimating lens, respectively. The first PBS beam splitter transmits 0° linearly polarized light and reflects 90° linearly polarized light, while the second PBS beam splitter transmits 45° linearly polarized light and reflects 135° linearly polarized light. The first and second light-shielding plate groups are respectively disposed on the output optical paths of the first and second PBS beam splitters and are used to selectively switch the optical paths on and off. A set of mirrors is used to refract light polarized at 0°, 90°, and 135°. Multiple light-combining prisms, each including a first light-combining prism, a second light-combining prism, and a third light-combining prism, wherein the first light-combining prism is located on the output optical path of the first light-shielding plate group, the second light-combining prism is located on the output optical path of the second light-shielding plate group, and the third light-combining prism is positioned to simultaneously receive the outgoing light from the first light-combining prism and the outgoing light from the second light-combining prism, and combines the two light paths for output; The polarization beam splitting system controls the opening and closing states of the first and second light-shielding plate groups to output four-angle polarized light at the third beam combining prism: 0°, 45°, 90°, and 135°.

2. The internal stress measurement device based on PBS spectroscopy according to claim 1, characterized in that: The first PBS beam splitter and the second PBS beam splitter have the same structure, and the second PBS beam splitter is installed with the optical axis rotated 45° relative to the first PBS beam splitter.

3. The internal stress measurement device based on PBS spectroscopy according to claim 1, characterized in that: The first, second, and third beam combining prisms have the same structure, each including four right-angle prism surfaces: a, b, c, and d. Surfaces a and c are coated with a film layer that reflects S-polarized light, used to reflect 0° and 90° polarized light, while surfaces b and d are coated with a film layer that transmits P-polarized light, used to transmit 45° and 135° polarized light.

4. The internal stress measurement device based on PBS spectroscopy according to claim 1, characterized in that: The first light-shielding plate group includes a first light-shielding plate and a second light-shielding plate. The first light-shielding plate controls the on / off state of the 90° polarized light path, and the second light-shielding plate controls the on / off state of the 0° polarized light path. The second light-shielding plate group includes a third light-shielding plate and a fourth light-shielding plate. The third light-shielding plate controls the on / off state of the 135° polarized light path, and the fourth light-shielding plate controls the on / off state of the 45° polarized light path.

5. The internal stress measurement device based on PBS spectroscopy according to claim 4, characterized in that: The first, second, third, and fourth light-shielding plates are each driven by a motor, thereby independently controlling the on / off state of polarized light at each angle.

6. The internal stress measurement device based on PBS spectroscopy according to claim 4, characterized in that: The reflector group includes a first reflector, a second reflector, a third reflector, a fourth reflector, and a fifth reflector. The first and second reflectors are located on the output optical path of the first light-shielding plate, the fourth and fifth reflectors are located on the output optical path of the third light-shielding plate, and the third reflector is located on the output optical path of the first beam combining prism, for receiving and refracting the light beam from the first beam combining prism.

7. The internal stress measurement device based on PBS spectroscopy according to claim 6, characterized in that: The first, second, third, fourth, and fifth reflectors are each coated with a silver or aluminum film.

8. The internal stress measurement device based on PBS spectroscopy according to claim 6, characterized in that: The third reflector is located on the output optical path of the first light combining prism and on the input optical path of the third light combining prism. The light reflected by the third reflector and the light output by the second light combining prism are both input to the third light combining prism.

9. A method for measuring internal stress based on PBS spectroscopy, characterized in that: The internal stress measuring device according to any one of claims 1-8 is used to test the sample. By switching the opening and closing states of the first light-shielding plate group and the second light-shielding plate group, four-angle polarized light of 0°, 45°, 90° and 135° is generated at the third light-combining prism and passes through the sample under test, the 1 / 4 wave plate and the analyzer in sequence. The imaging element collects four sets of interference images and transmits them to the image processing unit. The image processing unit calculates the stress value by background subtraction and brightness analysis.

10. The method for measuring internal stress based on PBS spectroscopy according to claim 9, characterized in that: The image processing unit performs the following steps: when there is no sample to be tested, it sequentially acquires background images of four-angle polarized light; after placing the sample, it sequentially acquires sample images of four-angle polarized light; after deducting background noise, it calculates the birefringence optical path difference based on the brightness difference and inverts the stress distribution.

Images