A device and method for detecting surface damage of optical components based on liquid crystal light valves

Abstract

A device and method for detecting surface damage to optical components based on a liquid crystal light valve are disclosed. The device uses a liquid crystal light valve to form a programmable dynamic Fresnel lens or grating, enabling a two-dimensional scanning of the entire surface of the sample under test by an illumination beam. Combined with fiber optic transmission and high-sensitivity detection, it achieves non-mechanical measurement of surface damage to the component. This device is characterized by its small size and lightweight design, and enables online, real-time, direct detection of surface damage after different levels of laser irradiation, providing accurate information for the component's damage status and timely replacement.

Description

Technical Field

[0001] This invention relates to the field of surface damage detection technology for optical components in high-power laser systems, specifically a surface damage detection device and method for optical components based on a liquid crystal light valve, which is applicable to online, in-situ, and real-time surface damage detection of optical components in high-power laser systems after high-energy laser irradiation. Background Technology

[0002] High-power laser systems play a crucial role in high-energy research, advanced instrumentation, and national defense. Numerous optical components within these systems suffer surface damage under the influence of high-energy laser light. This damage obstructs laser output, significantly reducing the system's output flux. Stray light generated also interferes with the operation of other components. Furthermore, surface damage alters the beam distribution, affecting beam quality. Under repeated high-energy laser irradiation, surface damage on optical components gradually increases, eventually leading to component failure or even complete system inoperability. Therefore, online detection and monitoring of surface damage on optical components within high-power laser systems are essential for dynamically managing surface conditions and providing a basis for timely component replacement.

[0003] Currently, the assessment of surface damage to optical components within high-power laser systems primarily relies on external visual inspection or energy sampling monitoring. Specifically, the system's output laser light is sampled and projected onto a screen via a sampling mirror. The human eye then observes the projected light spot for dark spots, abrupt changes in brightness, and the size of any obstructed areas to subjectively assess the damage to internal components. Alternatively, an energy measurement system is used to move and sample the energy distribution at different locations on the projected light spot, thereby assessing the damage to internal components. Both methods involve indirect external measurement, are affected by beam transmission, have limited accuracy, and cannot perform real-time detection after a single laser strike, making it impossible to accurately determine the rate of damage progression.

[0004] Currently, the detection of surface damage to optical components within high-power laser systems mainly relies on two methods:

[0005] One method is external visual inspection, which involves projecting the system's output laser onto a screen through a sampling lens. Operators then visually inspect the projected light spot for dark spots, abrupt changes in brightness, or obstructed areas, thus subjectively assessing the damage to internal components. However, this method is highly susceptible to human error, has poor accuracy, and cannot provide quantitative measurements.

[0006] The second method is energy sampling measurement, which involves moving an energy measurement probe to measure the energy distribution at different locations of the projected light spot, indirectly inferring the surface damage of the component. Although this method is an improvement over the visual method, it is still an external indirect measurement and is affected by diffraction and scattering effects in the laser transmission path, resulting in limited measurement accuracy.

[0007] Neither of the above two methods can perform real-time, in-situ, and direct detection of the component surface after a single high-energy laser attack, nor can they accurately track the damage growth process with each laser attack, thus limiting the system's effective management of the component's health status. Summary of the Invention

[0008] This invention aims to overcome the following shortcomings in existing methods for detecting surface damage to optical components within high-power laser systems: reliance on external indirect measurements (projection visual inspection or energy sampling), making online, in-situ, real-time, and objective detection of component surface damage impossible; difficulty in immediately acquiring the damage state after a single high-energy laser beam; inability to accurately track the damage growth process with each laser beam; and the large size and complex structure of existing detection devices, making them inconvenient for integration into high-power laser systems. This invention provides a surface damage detection device and method for optical components based on a liquid crystal light valve, achieving non-mechanical, miniaturized, high-precision, and programmable online scanning detection.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A device for detecting surface damage of optical components based on liquid crystal light valves

[0011] The device includes: an illumination source, a first coupler, an optical fiber, a second coupler, a bandpass filter, a liquid crystal light valve, a third coupler, a focusing lens, a photodetector, and a control processor.

[0012] The connection and positional relationships between the components are as follows:

[0013] The light output end of the lighting source is optically aligned with the incident end of the first coupler, the output end of the first coupler is coupled to one end of the optical fiber, and the other end of the optical fiber is coupled to the incident end of the second coupler and the output end of the third coupler, respectively.

[0014] The output end of the second coupler, the bandpass filter, and the liquid crystal light valve are arranged sequentially along the illumination light path, and the bandpass filter is located between the second coupler and the liquid crystal light valve.

[0015] The exit surface of the liquid crystal light valve is positioned facing the surface of the sample to be tested, so that the illumination beam modulated by the liquid crystal light valve directly irradiates the surface of the sample to be tested, or irradiates the surface of the sample to be tested through additional optical elements.

[0016] The scattered light from the surface of the sample under test passes sequentially through the liquid crystal light valve and the bandpass filter before entering the second coupler, and is then transmitted to the third coupler via the optical fiber.

[0017] The output end of the third coupler is optically aligned with the light-incident side of the focusing lens, and the light-outceasing side of the focusing lens is positioned facing the photosensitive surface of the photodetector.

[0018] The signal output terminal of the photodetector is electrically connected to the signal input terminal of the control processor, and the control signal output terminal of the control processor is electrically connected to the control terminal of the liquid crystal light valve.

[0019] The control processor is used to program and control the liquid crystal light valve to generate a dynamically adjustable beam modulation element, which is a Fresnel lens or a grating, and to control the liquid crystal light valve to refresh the parameters of the beam modulation element so as to realize the two-dimensional scanning of the focused light spot on the surface of the sample to be tested, while simultaneously acquiring the scattered light signal output by the photodetector.

[0020] Preferably, the illumination source is a narrowband light source; the transmission band of the bandpass filter matches the emission band of the illumination source to suppress stray light.

[0021] Preferably, the liquid crystal light valve is a reflective or transmissive spatial light modulator; the control processor generates a Fresnel lens by loading a phase map or amplitude map onto the liquid crystal light valve, wherein the Fresnel lens is of amplitude type or phase type.

[0022] As another preferred embodiment, the device further includes a lens disposed between the liquid crystal light valve and the sample to be tested; the control processor programs and controls the liquid crystal light valve to generate a grating, and the emitted light beam modulated by the liquid crystal light valve is focused onto the surface of the sample to be tested by the lens; the position of the focused spot on the surface of the sample to be tested is changed by changing the period parameter of the grating.

[0023] Preferably, the control processor is further configured to: set the focal length and center position coordinates of the Fresnel lens generated by the liquid crystal light valve, or set the period parameters of the grating, so as to control the two-dimensional scanning movement of the focused light spot on the surface of the sample to be tested; the step size of the two-dimensional scanning is equal to the diameter d of the focused light spot on the surface of the sample to be tested.

[0024] Surface damage detection method based on the above device

[0025] This method employs a control processor to program and control the liquid crystal light valve to dynamically generate a Fresnel lens or grating. By refreshing its parameters, the illumination spot performs a two-dimensional step-by-step scan on the surface of the sample under test without mechanical movement, simultaneously acquiring the scattered light signal at each scan point, reconstructing the damage distribution map, and achieving multi-shot comparative monitoring. Specifically, it includes the following steps:

[0026] Step 1. Initialize the scanning position: Turn on the illumination source, and the control processor modulates the liquid crystal light valve to generate a Fresnel lens or grating, and sets the corresponding parameters (focal length and center position coordinates of the Fresnel lens, or period parameters of the grating) so that the illumination beam is focused on the edge vertex position of the surface of the sample to be tested, which serves as the scanning start point.

[0027] Step 2. Generate a scanning coordinate array: The control processor generates an array of coordinate positions of the center of the focused spot for scanning movement. The scanning step size is equal to the diameter d of the focused spot on the surface of the sample to be tested, ensuring full-aperture coverage without omissions. The scanning coordinate array is represented as follows:

[0028]

[0029] Where (x1, y1) represents the starting position of the edge vertex scan. The distances along the x and y directions of the focused spot movement are respectively the diameters d of the illumination beam focused onto the sample surface by the Fresnel lens or grating and lens, i.e., x n -x n-1 =d,y m -y m-1 =d, n=1~N, m=1~M;

[0030] Step 3. Dynamic Refresh and Two-Dimensional Scanning: The control processor assigns scanning coordinates to the liquid crystal light valve sequentially, first in the x-axis and then in the y-axis. This dynamically refreshes the Fresnel lens center coordinates or grating period parameters generated by the liquid crystal light valve, causing the focused light spot to perform two-dimensional stepping motion on the surface of the sample under test, gradually covering the entire surface. Specifically, when the liquid crystal light valve generates a Fresnel lens, the focused light spot position is moved by changing the center coordinates of the Fresnel lens; when the liquid crystal light valve generates a grating and the device includes a lens, the focused light spot position is moved by changing the grating period parameters.

[0031] Step 4. Synchronously acquire scattered signals: Each time the Fresnel lens center coordinates or grating period parameters are changed, the control processor triggers the photodetector to synchronously acquire the scattered light signal generated at the current coordinate point, and stores the signal intensity in association with the current coordinates.

[0032] Step 5. Damage Image Reconstruction and Assessment: After completing the full-aperture scan, the control processor reconstructs the damage distribution image of the sample surface based on the two-dimensional distribution of the acquired scattering signals. Image processing algorithms are used to extract the location, area, and scattering intensity of the damage points to determine the severity of the surface damage. The image processing algorithms include: background subtraction, adaptive thresholding, morphological filtering, and connected component analysis.

[0033] Step 6. Multiple-shot damage growth monitoring: After the sample under test undergoes the next high-energy laser treatment, repeat steps 1) to 5), acquire the damage distribution image after this shot, and compare it point by point with the damage distribution image of the previous shot to determine the damage growth and whether it has reached the scrapping level. The specific determination method is as follows: Spatially match the damage points extracted in the current shot with the damage points in the previous shot. If the center distance between two damage points is less than 1.5 times the focused spot diameter d, they are considered as the same damage point; calculate the area growth coefficient (the ratio of the current area to the previous area) of each matched damage point; if a new damage point appears, or the area growth coefficient of the original damage point exceeds a preset threshold, an early warning signal is issued; if the proportion of the total damage area to the light transmission aperture of the sample under test exceeds a preset value, or the diameter of a single damage point exceeds a preset size, the sample under test is determined to have reached the scrapping level.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) This invention utilizes the programmable dynamic modulation characteristics of a liquid crystal light valve to achieve two-dimensional scanning of the focused light spot on the sample surface by electronically changing the center coordinates of the Fresnel lens or the grating period parameters. The entire scanning process has no moving mechanical parts, avoiding mechanical wear, vibration, and positioning errors, significantly improving the reliability and service life of the device, while also facilitating miniaturization and weight reduction.

[0036] 2) This invention employs optical fiber to transmit both illumination and scattered light. The illumination and scattering / collection light paths share core components such as optical fibers and liquid crystal light valves, achieving a true shared optical path structure. This design not only greatly simplifies the system architecture and reduces size and weight, but also allows the photodetector to be located away from the core area of ​​the high-power laser system, effectively avoiding high-energy laser interference.

[0037] 3) The device of this invention can be directly installed inside a high-power laser system, and immediately scans and detects the surface of the component after each high-energy laser beam, without disassembling the component or using external projection for sampling. The detection results are objective, quantitative, and repeatable, and can truly reflect the damage state of the component surface.

[0038] 4) The control processor has built-in image processing and damage growth analysis algorithms, which can automatically complete scanning, acquisition, image reconstruction, damage parameter extraction, multiple comparison and scrap determination, reducing manual intervention and improving the consistency and efficiency of detection.

[0039] 5) By tracking the location and area changes of damage points one by one, the occurrence, expansion and emergence of new damage points can be detected in a timely manner. Warnings can be issued before the damage to components reaches the scrap threshold, providing a quantitative basis for timely component replacement, thereby avoiding the shutdown or chain damage of the entire high-power laser system due to component failure.

[0040] 6) The present invention can flexibly adjust the scanning step length according to the sample aperture and detection accuracy requirements, and can select Fresnel lens mode (more compact structure) or grating + lens mode (smaller focused spot and faster scanning speed), which is suitable for different application scenarios.

[0041] The optical element surface damage detection device and method based on liquid crystal light valve provided by this invention realizes miniaturized, non-mechanically movable, online, in-situ, real-time, and quantitative detection of surface damage of optical elements in high-power laser systems, which has significant creative progress and industrial practical value. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the optical element surface damage detection device based on the Fresnel lens generated by the liquid crystal light valve according to the present invention;

[0043] Figure 2 This refers to the spot scanning method performed by liquid crystal light valve phase modulation in embodiments 1 and 2 of the present invention;

[0044] Figure 3 This is a schematic diagram of the optical element surface damage detection device based on the liquid crystal light valve generating grating of the present invention;

[0045] In the figure: 1-Illumination source; 2-First coupler; 3-Fiber optic cable; 4-Second coupler; 5-Bandpass filter; 6-Liquid crystal light valve; 7-Sample; 8-Third coupler; 9-Focusing lens; 10-Photodetector; 11-Control processor; 12-Lens. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. These embodiments are only for explaining the present invention and do not constitute any limitation on the scope of protection of the present invention. All equivalent substitutions or improvements made based on the concept of the present invention should be included within the scope of protection of the present invention.

[0047] Example 1

[0048] See Figure 1 , Figure 1 This is a schematic diagram of an optical element surface damage detection device based on a Fresnel lens generated by a liquid crystal light valve, provided in Embodiment 1 of the present invention. The device includes: an illumination source 1, a first coupler 2, an optical fiber 3, a second coupler 4, a bandpass filter 5, a liquid crystal light valve 6, a sample to be tested 7 (i.e., an optical element in a high-power laser system), a third coupler 8, a focusing lens 9, a photodetector 10, and a control processor 11.

[0049] The light beam emitted by the illumination source 1 enters the optical fiber 3 through the first coupler 2; after transmission through the optical fiber 3, the light beam exits from the second coupler 4 and illuminates the liquid crystal light valve 6 through the bandpass filter 5; the control processor 11 sets the liquid crystal light valve 6 to generate a Fresnel lens; after passing through the modulated liquid crystal light valve 6, the light beam is focused onto the surface of the sample 7; the scattered light generated by the damage on the surface of the sample 7 passes sequentially through the liquid crystal light valve 6, the bandpass filter 5, the second coupler 4 and the optical fiber 3, and exits from the third coupler 8, where it is focused by the focusing lens 9 onto the photodetector 10; the scattered light signal collected by the photodetector 10 is transmitted to the control processor 11.

[0050] In this embodiment, the illumination source 1 is a narrowband light source, matched with the bandpass filter 5. The bandpass filter 5 only allows illumination light to pass through, suppressing stray light generated by high-energy lasers and other ambient light in the high-power laser system. The control processor 11 loads a phase map or amplitude map into the liquid crystal light valve 6 via a standard video interface, thereby generating the required Fresnel lens phase distribution. The photodetector 10 is a silicon-based avalanche photodiode (APD) or photomultiplier tube (PMT), with a response band covering the illumination wavelength, adjustable gain, and nanosecond-level response speed. A pinhole aperture can be installed in front of the detector to limit the field of view and reduce background noise.

[0051] The method for surface damage detection using the above-mentioned liquid crystal light valve-based optical element surface damage detection device includes the following steps:

[0052] Step 1: System initialization and scan parameter settings

[0053] When the illumination source 1 is turned on, the control processor 11 modulates the liquid crystal light valve 6 to generate a Fresnel lens, sets the focal length and center position coordinates of the Fresnel lens, and focuses the incident illumination source onto the edge vertex position of the sample 7 to be tested.

[0054] Step 2: Generate scan coordinate array

[0055] The control processor 11 is programmed to set the center coordinate position array for the Fresnel lens scanning movement:

[0056]

[0057] Where (x1, y1) represents the starting position of the edge vertex scan. The distances along the x and y directions of the focused spot movement are respectively the diameters d of the illumination beam focused onto the sample surface by the Fresnel lens, i.e., x... n -x n-1 =d,y m -y m-1 =d, n=1~N, m=1~M;

[0058] Step 3: Generate Fresnel lens phase map and dynamically refresh it.

[0059] The control processor 11 assigns the center coordinates of the Fresnel lens to the liquid crystal light valve 6 in the order of first x and then y, so that the Fresnel lens generated by the liquid crystal light valve 6 is refreshed on the target surface of the liquid crystal light valve 6 and moves to different positions according to the coordinates, thereby making the focused light spot move in two dimensions on the surface of the sample 7 to cover the entire surface.

[0060] Step 4: Two-dimensional scanning and synchronous acquisition

[0061] Each time the coordinates of the Fresnel lens center are changed, the photodetector 10 synchronously collects the scattering signal generated at the corresponding coordinate point on the surface of the sample 7 and stores it in the control processor 11.

[0062] Step 5: Signal Processing and Damage Image Reconstruction

[0063] After completing the full-aperture scan and scattering signal acquisition, the control processor 11 uses an image processing algorithm to process the scattering signal distribution image obtained by the full-aperture scan, extracts the location and area of ​​the damage points on the surface of the sample 7 to be tested, and determines the severity of the damage to the sample surface; finally, it outputs a list of damage points, including location, area and relative scattering intensity.

[0064] Step 6: Analysis of the growth of multiple injuries

[0065] After the high-energy laser system completes the kth irradiation (k=1,2,3,…), steps 1-5 above are repeated to obtain the damage distribution map after that irradiation. The control processor 11 performs point-by-point matching between the damage points of the current irradiation and the damage points of the previous irradiation (k-1th irradiation). The matching rule is: if the center distance between two damage points is less than 1.5d, they are considered as the same damage point. The area growth coefficient (current area / previous area) of each matched damage point is calculated. If there are new damage points (no corresponding points in the previous irradiation) or the area of ​​existing damage points increases beyond a set threshold (e.g., area increases by 50%), a warning signal is issued. When the total damage area accounts for more than 5% of the sample's light transmission aperture or the diameter of a single damage point is greater than 1 mm, the sample is deemed to have reached the point of being scrapped, and immediate replacement is recommended.

[0066] In practical applications, the spot diameter d can be adjusted according to the sample aperture and detection accuracy requirements. A smaller d results in higher resolution but increases scanning time. Scanning time can be shortened by increasing the refresh rate of the liquid crystal light valve (e.g., using a high-speed DLP spatial light modulator, where the refresh rate can reach over 1 kHz) and employing parallel detection (e.g., an area array camera). Furthermore, for highly reflective samples, a dark-field detection mode can be used, i.e., adjusting the position of the focusing lens 9 to converge scattered light while deflecting specular reflection light away from the detector, further improving the signal-to-noise ratio.

[0067] Example 2

[0068] See Figure 3 , Figure 3 This is a schematic diagram of an optical element surface damage detection device based on a liquid crystal light valve generating a grating according to Embodiment 2 of the present invention. It mainly includes: an illumination source 1, a first coupler 2, an optical fiber 3, a second coupler 4, a bandpass filter 5, a liquid crystal light valve 6, a sample to be tested 7, a third coupler 8, a focusing lens 9, a photodetector 10, a control processor 11, and a lens 12. The difference from Embodiment 1 is that a lens 12 is added between the liquid crystal light valve 6 and the sample 7, and a programmable grating pattern is loaded on the liquid crystal light valve 6 instead of a Fresnel lens. The connection relationships of the other components (1-11) are the same as in Embodiment 1.

[0069] The light beam emitted by the illumination source 1 enters the optical fiber 3 through the first coupler 2; after transmission through the optical fiber 3, the light beam exits from the second coupler 4 and illuminates the liquid crystal light valve 6 through the bandpass filter 5; the control processor 11 sets the liquid crystal light valve 6 to generate a grating; after passing through the modulated liquid crystal light valve 6, the light beam passes through the lens 12 to the surface of the sample 7; the scattered light generated by damage on the surface of the sample 7 passes sequentially through the lens 12, the liquid crystal light valve 6, the bandpass filter 5, the second coupler 4 and the optical fiber 3, and exits from the third coupler 8, where it is focused by the focusing lens 9 onto the photodetector 10; the scattered light signal collected by the photodetector 10 is transmitted to the control processor 11.

[0070] The liquid crystal light valve 6 controls the light beam by generating a grating and lens 12 through the control processor 11.

[0071] A method for surface damage detection using the above-described apparatus, comprising the following steps:

[0072] 1) Turn on the illumination source 1, and program the control processor 11 to modulate the liquid crystal light valve 6 to generate a grating. Set the grating period parameters so that the incident illumination source is focused on the edge vertex position of the sample 7.

[0073] 2) The control processor 11 is programmed to set the grating period parameters to form the center coordinate position array of the scanning movement of the light spot:

[0074]

[0075] Where (x1, y1) is the starting position of the edge vertex scan. The distances the light spot moves along the x and y directions are the light spot diameters d of the illumination beam after passing through the grating and lens 12 to the sample surface, respectively. n -x n-1 =d,y m -y m-1=d, n=1~N, m=1~M;

[0076] 3) The control processor 11 sequentially assigns the grating period parameters to the liquid crystal light valve 6 in the order of first x direction and then y direction, so that the grating generated by the liquid crystal light valve 6 is refreshed on the target surface of the liquid crystal light valve 6 and then modulated by the lens 12, so that the light spot moves in two dimensions on the surface of the sample 7 to cover the entire surface.

[0077] 4) Each time the grating period parameter is changed, the photodetector 10 synchronously collects the scattering signal generated at the coordinate point corresponding to the surface of the sample 7 and stores it in the control processor 11.

[0078] 5) After completing the full-aperture scan and scattering signal acquisition, the control processor 11 uses an image processing algorithm to process the scattering signal distribution image obtained by the full-aperture scan, extracts the location and area of ​​the surface damage points of the sample 7, and determines the severity of the surface damage of the sample.

[0079] 6) After the sample is subjected to the next high-energy laser, steps 1) to 5) are repeated to obtain the location and area of ​​the damage points on the sample surface after the next laser. The location and area of ​​the damage points after the next laser are compared with the location and area of ​​the damage points after the previous laser to determine the growth of damage on the sample surface and whether the damage on the sample surface has reached the point of being scrapped.

[0080] In both embodiments, the scattered light is collected using a "common optical path" method: the scattered light generated by the damage points on the surface of the sample 7 is transmitted in reverse along the original illumination optical path, passing sequentially through the liquid crystal light valve 6, the bandpass filter 5, the second coupler 4, and the optical fiber 3, before being output from the third coupler 8 and then focused by the focusing lens 9 to the photodetector 10. This design utilizes the flexible transmission and coupling characteristics of the optical fiber 3, allowing the photodetector 10 to be located away from the core area of ​​the high-energy laser system, avoiding high-energy laser interference. The bandpass filter 5 further ensures that only the scattered light of the illumination wavelength enters the detector, while residual reflected light or plasma emission from the high-energy laser is effectively suppressed.

[0081] When the liquid crystal light valve 6 operates in reflection mode, both the illumination light and the scattered light pass through the same reflective surface of the liquid crystal light valve 6. This allows the separation of the illumination light and the scattered return light to be completed within the optical fiber, which can be a 3dB coupler, i.e., using the second coupler 4. Alternatively, the separation of the incident and outgoing light can be achieved through a spatial optical path using a semi-transparent mirror. These components are not shown in detail in the accompanying drawings, but those skilled in the art can supplement them based on common sense. For example, a semi-transparent mirror can be added between the second coupler 4 and the bandpass filter 5, coordinating with the phase modulation state of the liquid crystal light valve 6 to achieve transmit / receive isolation.

[0082] Experiments show that the optical element surface damage detection device and method based on liquid crystal light valve of the present invention can realize online in-situ measurement of surface damage of optical elements in high-power laser systems, providing key basis for the growth of surface damage and timely replacement of elements.

Claims

1. A device for detecting surface damage to optical components based on a liquid crystal light valve, characterized in that, include: Illumination source (1), first coupler (2), optical fiber (3), second coupler (4), bandpass filter (5), liquid crystal light valve (6), sample (7), third coupler (8), focusing lens (9), photodetector (10), control processor (11); The light beam emitted by the illumination source (1) enters the optical fiber (3) through the first coupler (2); after being transmitted through the optical fiber (3), it exits from the second coupler (4) and then shines on the liquid crystal light valve (6) through the bandpass filter (5); The exit surface of the liquid crystal light valve (6) is set facing the surface of the sample to be tested (7), so that the illumination beam modulated by the liquid crystal light valve (6) directly irradiates the surface of the sample to be tested (7), or irradiates the surface of the sample to be tested (7) through additional optical elements; the scattered light generated by the damage to the surface of the sample to be tested (7) passes through the liquid crystal light valve (6), the bandpass filter (5) and the second coupler (4) in sequence, and is transmitted through the optical fiber (3) to the third coupler (8), and then converged to the photosensitive surface of the photodetector (10) by the focusing lens (9); The signal output terminal of the photodetector (10) is electrically connected to the signal input terminal of the control processor (11), and the control signal output terminal of the control processor (11) is electrically connected to the control terminal of the liquid crystal light valve (6). The control processor (11) is used to program and control the liquid crystal light valve (6) to generate a dynamically adjustable beam modulation element, which is a Fresnel lens or a grating, and to control the liquid crystal light valve (6) to refresh the parameters of the beam modulation element so as to realize the two-dimensional scanning of the focused light spot on the surface of the sample (7) to be tested, while simultaneously acquiring the scattered light signal output by the photodetector (10).

2. The optical element surface damage detection device based on a liquid crystal light valve according to claim 1, characterized in that, The illumination source (1) is a narrowband light source; the transmission band of the bandpass filter (5) is matched with the emission band of the illumination source (1) to suppress stray light.

3. The optical element surface damage detection device based on a liquid crystal light valve according to claim 1, characterized in that, The liquid crystal light valve (6) is a reflective or transmissive spatial light modulator; the control processor (11) generates a Fresnel lens by loading a phase map or amplitude map onto the liquid crystal light valve (6), and the Fresnel lens is of amplitude type or phase type.

4. The optical element surface damage detection device based on a liquid crystal light valve according to claim 1, characterized in that, The additional optical element includes a lens (12), which is disposed between the liquid crystal light valve (6) and the sample to be tested (7); the control processor (11) programs and controls the liquid crystal light valve (6) to generate a grating, and the outgoing light beam modulated by the liquid crystal light valve (6) is focused onto the surface of the sample to be tested (7) by the lens (12); the position of the focused spot on the surface of the sample to be tested (7) is changed by changing the period parameter of the grating.

5. The optical element surface damage detection device based on a liquid crystal light valve according to claim 1, characterized in that, The control processor (11) is also used to: set the focal length and center position coordinates of the Fresnel lens generated by the liquid crystal light valve (6), or set the period parameters of the grating, so as to control the two-dimensional scanning movement of the focused spot on the surface of the sample to be tested (7); the step size of the two-dimensional scanning is equal to the diameter of the focused spot on the surface of the sample to be tested (7).

6. A method for surface damage detection using the surface damage detection device for optical elements based on liquid crystal light valves as described in any one of claims 1-5, characterized in that, This method uses the control processor (11) to program and control the liquid crystal light valve (6) to dynamically generate a Fresnel lens or grating, and refreshes its parameters to make the illumination spot perform a two-dimensional step scan on the surface of the sample to be tested (7) without mechanical movement, synchronously collect the scattered light signal of each scanning point, reconstruct the damage distribution map, and realize multiple comparative monitoring. The specific steps are as follows: Step 1) Turn on the illumination source (1), control the processor (11) to program and modulate the liquid crystal light valve (6) to generate a Fresnel lens or grating, and set the corresponding parameters to focus the illumination beam onto the edge vertex position of the surface of the sample to be tested (7). Step 2) The control processor (11) programs and sets the Fresnel lens center or grating period parameters to form a coordinate position array for scanning movement: Where (x1, y1) is the starting position of the edge vertex scan, and the distances the focused spot moves along the x and y directions are the diameters d of the spot focused onto the sample surface by the illumination beam through the Fresnel lens or grating and lens, respectively. n -x n-1 =d,y m -y m-1 =d, n=1~N, m=1~M; Step 3) The control processor (11) assigns the center coordinates of the scanning movement to the liquid crystal light valve (6) in the order of first x and then y, so that the Fresnel lens center coordinates or grating period parameters generated by the liquid crystal light valve (6) are dynamically refreshed, so that the focused light spot moves in two dimensions on the surface of the sample to be tested (7) and covers the entire surface to be tested point by point. Step 4) Each time the Fresnel lens center coordinates or grating period parameters are changed, the control processor (11) triggers the photodetector (10) to synchronously collect the scattered light signal generated at the current coordinate point and store the signal intensity in association with the current coordinates; Step 5) After completing the full-aperture scan and scattering signal acquisition, the control processor (11) reconstructs the damage distribution image of the surface of the sample to be tested (7) based on the two-dimensional distribution of the acquired scattering signal, and uses image processing algorithms to extract the location and area of ​​damage points on the surface of the sample (7) to determine the severity of damage to the sample surface. Step 6) After the sample to be tested (7) is subjected to the next high-energy laser, repeat steps 1) to 5) to obtain the location and area of ​​the damage points on the sample surface after the next laser attack, and compare them with the location and area of ​​the damage points in the previous laser attack to determine the damage growth of the sample surface and whether it has reached the scrapping level.

7. The method for surface damage detection according to claim 6, characterized in that, When the liquid crystal light valve (6) generates a Fresnel lens, the position of the focused spot is moved by changing the center coordinates of the Fresnel lens in step 3); when the liquid crystal light valve (6) generates a grating and the device includes a lens (12), the position of the focused spot is moved by changing the period parameters of the grating in step 3).

8. The method for surface damage detection according to claim 6, characterized in that, The image processing algorithm described in step 5) includes: background subtraction, adaptive thresholding, morphological filtering, and connected component analysis, to accurately extract the location, area, and relative scattering intensity of damage points from the scattering signal distribution.

9. The method for surface damage detection according to claim 6, characterized in that, The specific method for determining the damage growth in step 6) is as follows: Spatial matching is performed between the damage points extracted in the current shot and the damage points in the previous shot. If the center distance between the two damage points is less than 1.5 times the focused spot diameter d, they are considered to be the same damage point. Calculate the area growth factor for each matched damage point, which is the ratio of the current area to the previous area; If new damage points appear, or if the area growth coefficient of existing damage points exceeds a preset threshold, an early warning signal will be issued. If the total damaged area accounts for more than a preset value of the light transmission aperture of the test sample (7), or the diameter of a single damaged point exceeds a preset size, then the test sample (7) is determined to be scrapped.

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