Method for evaluating sub-surface damage performance of fused quartz highlight element

Abstract

The invention relates to the technical field of intense laser optical element processing, and discloses a fused quartz intense light element subsurface damage performance evaluation method, which comprises the following steps: making a pit on the surface of a to-be-detected element by utilizing the characteristic that no additional crack is generated in magnetorheological polishing so as to expose a subsurface damage layer of the to-be-detected element; performing acid etching on the to-be-tested element to remove a hydrolysis layer formed on the surface of the to-be-tested element through magneto-rheological polishing; measuring the slope contour line of the magnetorheological pit; carrying out a photo-thermal weak absorption test and a fluorescence test on the subsurface of the to-be-tested element from shallow to deep along the inclined plane contour line of the magneto-rheological pit; and determining the depth of the sub-surface damage layer of the to-be-detected element according to the horizontal distance of extension of the sub-surface damage of the to-be-detected element and the inclined plane profile of the magnetorheological pit. Through combination of magneto-rheological polishing pit making, acid etching treatment and photo-thermal weak absorption and fluorescence testing along the inclined surface of the pit, direct association among subsurface depth, defect distribution and laser damage performance is established, so that the problems of single characterization defect type and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of high-power laser optical element processing technology, and in particular, to a method for evaluating the subsurface damage performance of fused silica high-power optical elements. Background Technology

[0002] Fused silica, due to its excellent optical properties, is widely used in high-performance laser systems. In these systems, high-intensity optical components typically need to withstand extremely high laser energy fluxes. When the laser flux exceeds the component's tolerance limit, laser-induced damage occurs, leading to component failure. This limit is usually measured using the laser-induced damage threshold (LIDT). Although the theoretical LIDT of fused silica itself is high, in practical applications, the measured LIDT of components is often much lower than the theoretical value. Research indicates that the main reason for this is various defects introduced during the component's manufacturing process.

[0003] Among various manufacturing defects, those located on the subsurface of components, such as microcracks and impurities, are most sensitive to laser damage. These defects become strong absorption centers for laser energy, leading to localized energy deposition. When the deposited energy exceeds the material's limit, damage occurs. Therefore, in the post-processing of components, these subsurface damage layers must be completely removed to improve their laser load capacity. However, post-processing is typically costly and time-consuming. To optimize post-processing and improve processing efficiency while ensuring effective defect removal, accurate and efficient evaluation of subsurface defects generated by preceding processing steps (such as grinding and polishing) is necessary.

[0004] Currently, various detection techniques exist for subsurface damage, such as cross-sectional microscopy, angular polishing, and magnetorheological polishing spot methods. These traditional methods primarily rely on optical microscopes to observe subsurface cracks and measure their geometric dimensions. However, they typically have the following limitations: First, the detection content is relatively limited, mainly focusing on crack defects, making it difficult to comprehensively reflect the distribution and impact of other types of subsurface defects (such as impurity contamination and amorphous layers). Second, the measurement results are mainly based on geometric morphology information and cannot be directly converted into damage performance characteristic parameters that are instructive for component performance (especially laser damage threshold), making it difficult to directly serve manufacturing decisions for components with high damage thresholds. Finally, with the advancement of manufacturing technologies such as grinding, the size of subsurface defects has entered the submicron and even nanoscale, posing a significant challenge to the measurement accuracy and reliability of traditional methods that rely on subjective judgment under a microscope, making it difficult to meet the requirements of high-precision manufacturing process control.

[0005] In summary, existing subsurface damage detection technologies have shortcomings in terms of the comprehensiveness of defect type characterization, the correlation between measurement results and final performance, and the detection accuracy when dealing with micro- and nano-scale defects. Therefore, there is an urgent need to develop a novel subsurface damage performance evaluation method that can not only effectively characterize the distribution of subsurface defects at different depths, but also establish a direct correlation between "post-processing subsurface depth—subsurface defects—laser damage performance," thereby providing a direct, accurate, and reliable decision-making basis for the precision manufacturing and post-processing of fused silica high-intensity optical elements. Summary of the Invention

[0006] This invention provides a method for evaluating the subsurface damage performance of fused silica high-intensity optical elements. By combining magnetorheological polishing to create pits, acid etching treatment, and photothermal weak absorption and fluorescence testing along the pit slope, a direct correlation is established between subsurface depth, defect distribution, and laser damage performance. This solves the technical problems of traditional detection methods, such as limited defect type characterization, weak correlation between results and performance, and insufficient accuracy in detecting micro- and nano-scale defects.

[0007] This invention provides a method for evaluating the subsurface damage performance of fused silica high-intensity optical element, comprising the following steps: S100, selecting points on the surface of the element under test, and utilizing the characteristic that magnetorheological polishing does not produce additional cracks to create pits on the surface of the element under test to expose the subsurface damage layer of the element under test; S200, performing acid etching on the element under test to remove the hydrolysis layer formed on the surface of the element under test by magnetorheological polishing; S300, measuring the contour line of the inclined surface of the magnetorheological pit; S400, performing photothermal weak absorption test and fluorescence test on the subsurface of the element under test from shallow to deep along the contour line of the inclined surface of the magnetorheological pit; S500, determining the depth of the subsurface damage layer of the element under test based on the horizontal distance of the subsurface damage extension and the contour line of the inclined surface of the magnetorheological pit.

[0008] Furthermore, a step of cleaning the surface of the component under test is added before step S100. Specifically, when cleaning the surface of the component under test, deionized water is used for ultrasonic cleaning; the ultrasonic cleaning temperature is controlled at 30℃, and cleaning is performed sequentially at frequencies of 40KHz for 5 minutes, 80KHz for 5 minutes, 120KHz for 5 minutes, 160KHz for 5 minutes, 200KHz for 5 minutes, 240KHz for 5 minutes, and 270KHz for 5 minutes; after ultrasonic cleaning, nitrogen is used for drying.

[0009] Further, the magnetorheological polishing in step S100 is specifically as follows: two points are randomly selected on the surface of the component to be tested for magnetorheological polishing, creating two magnetorheological pits. The process parameters for magnetorheological polishing are: polishing wheel speed 120r / min-160r / min, flow rate 240L / min-280L / min, magnetic field current 6A-10A, and pressure depth 0.1mm-0.3mm.

[0010] Further, in step S200, the device under test is acid-etched, specifically: when acid etching the device under test, 5% hydrofluoric acid is used to perform static shallow etching on the device under test, and the surface of the device under test is etched with hydrofluoric acid for 10-15 minutes.

[0011] Furthermore, after acid etching, the device under test is rinsed with deionized water for 4-8 minutes and then quickly dried with nitrogen to prevent water residue.

[0012] Further, the measurement of the inclined contour line of the magnetorheological pit in step S300 specifically involves: using a three-dimensional profilometer to perform one-dimensional measurement of the centerline contour of the magnetorheological pit of the component, and obtaining position information corresponding to different depths.

[0013] Further, step S400 specifically includes: S401, performing a photothermal weak absorption test on the region where the magnetorheological pit is located on the surface of the component under test, obtaining the photothermal weak absorption change curve on the central contour line of the magnetorheological pit, and recording the horizontal distance at which the absorption rate peak disappears. l a Fluorescence testing was conducted on test areas sequentially from shallow to deep, and the horizontal distance at which the fluorescence signal of subsurface defects of the test element disappeared was recorded. l f .

[0014] Furthermore, the photothermal weak absorption test in step S401 is specifically as follows: a transmission mode is used, the test laser wavelength is 355nm, the power is 4W, the step interval is 50μm, and the scanning area covers the magnetorheological pit.

[0015] Further, the fluorescence test in step S402 specifically involves: a laser power of 40mW, a fluorescence imaging objective magnification of 20×, and a field of view of 120μm×120μm.

[0016] Further, step S500 specifically involves: when determining the depth of the subsurface damage layer of the device under test based on the horizontal distance of the subsurface damage extension and the inclined profile of the magnetorheological pit, comparing the horizontal distance at which the absorption rate peak disappears. l a The horizontal distance from the disappearance of fluorescence signals of subsurface defects l f Take the horizontal distance at which the subsurface defect disappears. lmax =max( l a , l f Then, comparing the horizontal distance to the centerline profile of the magnetorheological pit... l max The corresponding depth h is the measured subsurface damage layer depth SSD.

[0017] The present invention has the following beneficial effects:

[0018] 1. In terms of exposing and characterizing defects: The pitting effect of magnetorheological polishing without additional damage can be used to expose the subsurface region that changes continuously from the surface to the interior without introducing new cracks, thus creating a physical basis for comprehensive detection. The subsequent acid etching step effectively removes the hydrolysis layer generated by polishing, avoiding the obscuring or influence of this surface interference on the subsequent optical test signals, thereby ensuring that the detected signals truly reflect the original manufacturing defects.

[0019] 2. In terms of performance correlation assessment: The method of this invention performs a scanning test from shallow to deep along the pit slope with a known contour; the photothermal weak absorption test can directly detect the absorption characteristics of subsurface defects (such as impurities and cracks) to light energy, which is one of the key physical factors inducing laser damage; the fluorescence test can sensitively detect the defect energy level and impurity state related to damage; by correlating and mapping the results of these two optical performance tests with the precisely measured slope depth-position contour, the "defect optical performance characteristics" curves at different depths can be directly obtained, such as the absorption coefficient distribution and fluorescence intensity distribution; the abstract damage performance is quantified into a measurable physical signal distributed along the depth, thereby establishing a correlation between "subsurface depth-defect optical performance (strongly correlated with the laser damage threshold)", which solves the problem that traditional methods can only provide geometric morphology but cannot correlate performance.

[0020] 3. In terms of improving detection accuracy and universality: The method of this invention does not rely on human eye microscope observation, avoiding subjective errors, and is especially suitable for evaluating defects at the micro-nano scale; photothermal and fluorescence tests are sensitive to a variety of defects such as cracks and impurities, overcoming the limitation of traditional methods in detecting only one type of defect, and realizing a more comprehensive evaluation of subsurface damage performance.

[0021] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of a preferred embodiment of the method for evaluating the subsurface damage performance of fused silica high-intensity optical elements. Figure 2 This is a physical image of the sample surface and magnetorheological pits after HF shallow etching according to a preferred embodiment of the present invention; Figure 3 This is a contour diagram of the central axis of the magnetorheological pit according to a preferred embodiment of the present invention; Figure 4 This is a photothermal absorption signal diagram of the surface magnetorheological pit region according to a preferred embodiment of the present invention; Figure 5 This is a graph showing the evolution of the absorptivity along the central axis of the magnetorheological pit in a preferred embodiment of the present invention. Figure 6 This is a diagram illustrating the evolution of fluorescence damage along the central axis of the magnetorheological pit in a preferred embodiment of the present invention. Figure 6 (a) is a cluster damage map. Figure 6 (b) is a diagram showing the disappearance of cluster damage. Figure 6 (c) shows the sporadic distribution of damage. Figure 6 (d) shows a graph where the number of damages is continuously decreasing. Figure 6 (e) is a diagram showing the disappearance of damage. Detailed Implementation

[0023] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0024] like Figure 1As shown, the subsurface damage performance evaluation method for fused silica high-intensity optical element in this embodiment includes the following steps: S100, selecting points on the surface of the element under test, and using the characteristic that magnetorheological polishing does not produce additional cracks, creating pits on the surface of the element under test to expose the subsurface damage layer of the element under test; S200, acid etching of the element under test to remove the hydrolysis layer formed on the surface of the element under test by magnetorheological polishing; S300, measuring the contour line of the inclined surface of the magnetorheological pit; S400, performing photothermal weak absorption test and fluorescence test on the subsurface of the element under test from shallow to deep along the contour line of the inclined surface of the magnetorheological pit; S500, determining the depth of the subsurface damage layer of the element under test based on the horizontal distance of the subsurface damage extension and the contour line of the inclined surface of the magnetorheological pit. This invention provides a method for evaluating the subsurface damage performance of fused silica high-intensity optical elements. Step S100, magnetorheological polishing, creates a pit with continuously varying depth without disturbance. Utilizing the shear removal mechanism of magnetorheological polishing, rather than brittle fracture, a gently sloping pit with continuously varying depth can be created on the surface of the element under test without introducing additional damage such as secondary cracks. This exposes the subsurface damage layers at different depths that were originally buried below the surface in situ, continuously, and without interference, providing a basis for subsequent point-by-point and layer-by-layer detection. This method solves the problem that traditional cross-sectional methods (such as fracture methods) introduce new damage, thus contaminating the original defect information. Step S200, acid etching, eliminates surface interference and ensures the authenticity of the detection signal. During magnetorheological polishing, a very thin hydrolytic layer (or bainite layer) with different physicochemical properties from the bulk may form on the fused silica surface. This thin layer may absorb the detection laser or generate fluorescence background noise, interfering with the identification of the original subsurface defect signal. By selectively removing this interfering layer through acid etching, it is ensured that the subsequent photothermal and fluorescence test signals originate directly and purely from the original subsurface damage to be evaluated, improving the detection signal-to-noise ratio and the accuracy of the results. Step S300, measuring the inclined plane contour, establishes a high-precision spatial coordinate system. By accurately measuring the inclined plane contour of the magnetorheological pit, the lateral (horizontal) position of any test point within the pit can be uniquely and accurately mapped to a longitudinal (depth) coordinate. This provides a precise geometric transformation basis for mapping subsequent test results to specific depth information, thereby facilitating the realization of "depth-performance" correlation evaluation.Step S400 involves performing photothermal weak absorption and fluorescence tests along the inclined plane to obtain multidimensional physical signals directly related to laser damage performance. By detecting the slight temperature rise or thermal radiation of the subsurface material under the detection laser irradiation, the absorption characteristics of the laser energy at that point can be quantitatively characterized. Subsurface defects such as cracks, impurities, and amorphous phases are usually strong absorption sources. Therefore, this multidimensional physical signal directly reflects the sensitivity of the material at a specific depth to thermal damage induced by strong laser irradiation. The fluorescence test, by detecting the fluorescence signal generated under laser excitation of a specific wavelength, can sensitively identify the defect energy level, chemical bond state, and impurity type (such as oxygen vacancies, metal ions, etc.) related to subsurface damage. The characteristics and intensity of the fluorescence signal are directly related to the type, density, and activation state of the defects, and are another key physical parameter for evaluating the material's resistance to laser damage. The scanning test along the inclined plane from shallow to deep obtains continuous curves of the absorption coefficient distribution and fluorescence characteristic distribution, two performance parameters strongly correlated with the damage threshold, as a function of depth. Step S500 determines the depth of the subsurface damage layer. Based on performance criteria, the boundary of the damage layer is objectively determined. Combining the depth coordinates from step S300 and the performance signal curve from step S400, the variation of performance signals (such as absorption coefficient and intensity of specific fluorescence peaks) with depth can be analyzed. When the signal moves from the abnormal (high absorption, strong fluorescence) region to the stable (low absorption, intrinsic fluorescence) bulk material region, the corresponding depth can be determined as the effective depth of the subsurface damage layer. This depth is determined based on changes in physical properties rather than the morphological boundary observed by the human eye, thus reflecting the actual influence range of the damage layer that affects the laser damage threshold more directly and objectively. Traditional methods (such as cross-sectional microscopy) can only provide geometric information such as crack length and density. However, this invention introduces photothermal absorption and fluorescence, two detection methods directly related to the physical processes of laser damage (energy absorption and defect excitation), upgrading the evaluation object from the morphology of the defect to its optical functional characteristics. This allows the evaluation results to directly predict and correlate the laser damage threshold of the component, providing a more scientific basis for post-processing decisions. The method of this invention correlates and continuously scans depth information (through inclined plane contour measurement) and performance information (through optical testing) point by point on the inclined plane, ultimately forming a quantitative curve of performance parameters distributed with depth. This overcomes the problems of discontinuous information and low efficiency of traditional point measurement or layer-by-layer methods, achieving high-resolution, visual, and quantitative characterization of subsurface damage performance. Photothermal and fluorescence testing are extremely sensitive to absorbent defects and point defects at the micron and even nanoscale, and their detection limits are far superior to the resolution limits of optical microscopes and the recognition capabilities of the human eye. Therefore, the method of this invention can effectively evaluate subsurface damage of even smaller scales caused by advanced manufacturing processes, solving the accuracy bottleneck of traditional microscopic observation methods at the micro-nano scale.Magnetorheological pitting causes no additional damage, and acid etching removes the interfering layer, ensuring the authenticity of the object under test. A single pitting and scanning process can obtain a complete performance-depth curve from the surface to the bulk of a test point, with a simple process flow and high information acquisition efficiency. The method of this invention utilizes the non-destructive characteristics of magnetorheological polishing to create pits, which can non-destructively expose the continuously changing subsurface region from the surface to the interior without introducing new crack interference, creating a physical basis for comprehensive detection. The subsequent acid etching step effectively removes the hydrolytic layer generated by polishing, avoiding the obscuring or influence of this surface interference on subsequent optical test signals, thereby ensuring that the detected signals truly reflect the original manufacturing defects. This invention employs a scanning test along a known contoured sloping surface, proceeding from shallow to deep. The photothermal weak absorption test directly detects the light absorption characteristics of subsurface defects (such as impurities and cracks), a key physical factor inducing laser damage. The fluorescence test sensitively detects defect energy levels and impurity states related to damage. By mapping these two optical performance test results to a precisely measured sloping surface depth-position profile, "defect optical performance characteristic" curves at different depths, such as absorption coefficient distribution and fluorescence intensity distribution, can be directly obtained. This quantifies abstract damage performance into measurable physical signals distributed along depth, establishing a correlation between "subsurface depth-defect optical performance (strongly correlated with laser damage threshold)," solving the problem that traditional methods can only provide geometric morphology without correlating performance. This invention does not rely on human microscopic observation, avoiding subjective errors, and is particularly suitable for evaluating micro / nano-scale defects. The photothermal and fluorescence tests are sensitive to various defects such as cracks and impurities, overcoming the limitation of traditional methods that only detect a single defect type, and achieving a more comprehensive evaluation of subsurface damage performance. This method uses a technical chain of "non-destructive pit making - surface cleaning - contour mapping - optical performance scanning" to spatially correlate the depth information of the subsurface with optical performance parameters that directly reflect the sensitivity to laser damage. This enables an accurate, comprehensive, and quantitative assessment of the subsurface damage performance of fused silica high-intensity optical elements, providing a direct and reliable performance basis for determining the depth of the damage layer to be removed in subsequent processes, and ultimately serving the manufacturing of high-damage-threshold optical elements.

[0025] In this embodiment, a surface cleaning step for the component under test is added before step S100. Specifically, when cleaning the surface of the component under test, deionized water is used for ultrasonic cleaning; the ultrasonic cleaning temperature is controlled at 30℃, and cleaning is performed sequentially at frequencies of 40KHz for 5 minutes, 80KHz for 5 minutes, 120KHz for 5 minutes, 160KHz for 5 minutes, 200KHz for 5 minutes, 240KHz for 5 minutes, and 270KHz for 5 minutes; after ultrasonic cleaning, nitrogen is used for drying. This eliminates the systematic error caused by the original surface contamination of the component under test to the subsequent subsurface damage performance evaluation results; through a refined cleaning process, targeted removal of surface contaminants of different particle sizes and attachment morphologies is achieved, thereby ensuring that the subsequent detection signal purely reflects the subsurface defects introduced by the manufacturing process, rather than surface deposits. Ultrasonic cleaning using deionized water avoids secondary contamination and provides a pure medium for cavitation. Deionized water contains little to no soluble ions, preventing impurities from leaving residues on component surfaces and forming new contaminants or water stains. This pure water medium is fundamental to ensuring efficient and uniform ultrasonic cavitation, reducing the risk of uneven cleaning or chemical contamination of component surfaces due to impurities. A step-by-step, frequency-based ultrasonic cleaning process selectively and progressively removes surface contaminants of different sizes and adhesion, improving the comprehensiveness and thoroughness of the cleaning. The principle of ultrasonic cleaning relies primarily on cavitation; the size and energy of cavitation bubbles are directly related to the frequency of the ultrasound. Low-frequency cleaning (e.g., 40kHz, 80kHz) produces larger cavitation bubbles with higher energy release upon collapse, but lower cavitation bubble density. Utilizing strong impact force and microjets, it effectively removes firmly attached large particles (such as grinding debris and dust) and strongly adhesive organic films. Starting cleaning at a lower frequency allows for the initial peeling and removal of macroscopic, strongly adhered contaminants. The contamination layer creates conditions for subsequent fine cleaning, preventing large particles from scratching the surface during high-frequency cleaning. High-frequency (e.g., 120kHz to 270kHz) cleaning produces cavitation bubbles that are small in size and high in density, but have low single-bubble collapse energy. By utilizing the penetration and oscillation of dense micro-cavitation bubbles, it effectively removes loosely attached micron and submicron-sized fine particles, as well as molecular-level thin-layer contamination adsorbed by van der Waals forces. As the frequency gradually increases, the characteristic size of the removable contaminants gradually decreases. Through a stepwise scanning from low to high frequency, it can cover a broad spectrum of contaminants, from large particles to fine attachments, achieving stepwise and deep cleaning of multi-scale surface contamination.The cleaning temperature is controlled at 30℃, striking a balance between optimizing the cleaning effect and ensuring process controllability. Temperature is a key parameter affecting the ultrasonic cavitation effect and the physicochemical properties of the cleaning fluid, and 30℃ is a mild and controllable temperature setting. Compared to room temperature (such as 20℃-25℃), moderately raising the temperature (to 30℃) can reduce the surface tension and viscosity of the cleaning fluid (deionized water), which is conducive to the generation and collapse of cavitation bubbles and can enhance the wetting and penetration ability of the cleaning fluid to contaminants (especially organic matter), thereby improving cleaning efficiency. This temperature is much lower than the boiling point of water, which can avoid the cavitation threshold from rising sharply due to excessive temperature, weakening the cavitation effect, or causing water to evaporate rapidly and leave watermarks on the surface of the component. This temperature has no effect on the physical properties of the fused silica component itself and is easy to control accurately and stably in the equipment, ensuring the stability and repeatability of the process. After ultrasonic cleaning, nitrogen is used for drying, achieving rapid drying without contact or residue, avoiding secondary pollution caused by liquid evaporation. Using high-purity nitrogen is a physical drying method. Compared with natural air drying or oven drying, the high-speed, clean nitrogen flow directly removes the water film from the component surface, avoiding the formation of spots, water stains, or adsorption of new contaminants on the component surface due to trace amounts of solutes remaining in the water or dust in the air during slow evaporation of water on the surface. As an inert gas, nitrogen is chemically stable and will not react with the fused silica surface, thus ensuring that the high cleanliness of the surface is maintained after cleaning, providing a clean and dry starting surface for the subsequent magnetorheological polishing pit-making steps.

[0026] In this embodiment, the magnetorheological polishing in step S100 specifically involves randomly selecting two points on the surface of the component under test for magnetorheological polishing, creating two magnetorheological pits. The process parameters for magnetorheological polishing are: polishing wheel speed 120 r / min-160 r / min, flow rate 240 L / min-280 L / min, magnetic field current 6 A-10 A, and depth of 0.1 mm-0.3 mm. By randomly selecting two points and creating two pits, a balance is achieved between the representativeness of the evaluation results and the controllability and repeatability of the process. Without causing additional damage to the component under test, magnetorheological pits that meet the requirements of subsequent depth-performance correlation testing are manufactured efficiently and stably, thus laying the technological foundation for obtaining statistically significant subsurface damage performance evaluation data. By randomly selecting two points on the surface of the component under test for magnetorheological polishing, two magnetorheological pits are created, improving the representativeness and reliability of the evaluation results and reducing the risk of misjudgment due to the randomness of single-point detection. The subsurface damage distribution of optical components may exhibit spatial non-uniformity due to factors such as the uniformity of previous grinding and polishing processes, fluctuations in process parameters, and tool wear. Detecting pits at only a single location may only yield results (damage depth, performance curve) that are specific to that location and cannot represent the overall or typical condition of the component. However, the method of this invention increases the spatial coverage of sampling by randomly selecting at least two points for pit detection. By comprehensively considering the detection results of the two points (e.g., taking the larger value, the average value, or analyzing its distribution range), a more reliable evaluation conclusion that better reflects the overall subsurface damage characteristics of the component can be obtained than that of single-point detection. This makes subsequent post-processing decisions (such as polishing removal depth) more safe and universal. Limiting the specific process parameters of magnetorheological polishing to ensure that the formation quality of magnetorheological pits meets the requirements of "no additional damage, controllable contour, high efficiency and stability" is a prerequisite for achieving all subsequent inspection steps. The polishing wheel speed of 120r / min-160r / min directly affects the linear velocity of the polishing wheel driving the magnetorheological polishing fluid to act on the workpiece surface, balancing removal efficiency and processing stability. This is beneficial for obtaining a stable and controllable material removal process while ensuring a certain removal efficiency. Too low a speed may lead to insufficient removal efficiency and prolong pit formation time; too high a speed may cause unstable effective retention of polishing fluid due to centrifugal force or generate unnecessary fluid disturbance, affecting the smoothness and consistency of the pit slope contour.A flow rate of 240L / min-280L / min determines the sufficiency and renewal rate of the magnetorheological polishing slurry, maintaining the stability of the slurry composition, viscosity, and flow state in the polishing zone. This helps to form a continuous, stable, and uniformly composed flexible polishing head, thereby achieving smooth removal without subsurface damage. Insufficient flow rate may lead to insufficient slurry supply, uneven distribution of abrasive and carbonyl iron powder, affecting the consistency of polishing results, and even causing micro-scratches due to local overheating or insufficient abrasive. Excessive flow rate may cause fluid impact, affecting the stability of the polishing zone and resulting in unnecessary material waste. The magnetic field current of 6A-10A directly determines the strength of the electromagnetic field, which in turn controls the rheological properties (stiffness, shear stress) of the magnetorheological polishing slurry. This provides a sufficiently flexible and controllable grinding head, ensuring that the polishing slurry can efficiently remove material while maintaining good compliance and shear removal characteristics, thus preventing the formation of additional cracks. If the current is too low, the magnetic field is too weak, and the polishing slurry cannot form a sufficiently rigid flexible grinding head, resulting in low removal efficiency and potential instability. If the current is too high, the polishing slurry becomes too rigid, and its behavior may resemble that of a bonded abrasive, losing the shear removal advantage unique to magnetorheological polishing and increasing the risk of additional subsurface cracks or scratches. A depth of 0.1mm-0.3mm controls the interference between the polishing wheel and the workpiece surface, directly affecting the polishing pressure. This balances material removal rate and surface quality, helping to maintain a stable polishing contact state while achieving a reasonable removal rate and forming the required pit depth. This ensures smooth pit walls and provides a good foundation for subsequent accurate measurement of the inclined plane profile and optical scanning. Too little depth results in a low removal rate and poor pit-making efficiency; too much depth leads to excessive polishing pressure, potentially altering the stable flow field of the magnetorheological fluid, inducing unstable material removal, and even causing localized stress concentration, violating the principle of no additional damage. Optionally, and not limited to just two magnetorheological pits, more pits can be created. Optionally, two points on the surface of the component under test are selected for magnetorheological polishing to create two polishing pits. The process parameters are: polishing wheel speed 140r / min, flow rate 260L / min, magnetic field current 8A, and depth of 0.2mm.

[0027] In this embodiment, the acid etching of the device under test in step S200 specifically involves using 5% hydrofluoric acid for static shallow etching of the device under test for 10-15 minutes. By limiting the low-concentration, static, and short-duration hydrofluoric acid etching process, the hydrolytic layer formed after magnetorheological polishing can be removed precisely, controllably, and selectively. Simultaneously, the impact of the acid etching process on the device material (especially the subsurface damage layer to be evaluated) is minimized, thereby ensuring that subsequent optical test signals can accurately and completely reflect the performance characteristics of the original subsurface damage and avoiding the introduction of new interference due to excessive or improper acid etching. Using 5% hydrofluoric acid achieves highly selective and controllable removal of the hydrolyzed layer while maximizing the protection of the component's structure. Hydrofluoric acid is one of the few acids that can effectively react with fused silica (mainly composed of SiO2). The low concentration of 5% results in a lower concentration of activated HF molecules and ions in the reaction solution, leading to a moderate and controllable reaction rate. This avoids excessive erosion of the substrate material caused by overly vigorous reactions at high concentrations, making the etching process easily controllable through time parameters. This enhances the selectivity of removal. The hydrolyzed layer formed by magnetorheological polishing is typically a loosely structured, silanol-rich (-SiOH) or hydrated amorphous SiO2 thin layer, whose chemical activity is far higher than that of the structurally complete and dense fused silica substrate. The low concentration of hydrofluoric acid preferentially reacts with the highly active hydrolyzed layer, effectively removing this thin layer while minimizing additional erosion of the underlying, relatively intact subsurface damage layer and substrate material, achieving targeted cleaning. Static shallow etching ensures the uniformity and consistency of the etching process and clearly defines the etching target as only surface interference. Static means that the acid solution and the device surface remain relatively still during the etching process, without stirring or flowing. This method avoids local mass transfer unevenness caused by fluid disturbance, thereby achieving a consistent etching rate across the entire surface of the device under test (especially inside the magnetorheological pit). Uniform etching is a prerequisite for obtaining stable and reliable subsequent test results, avoiding different signal baselines in different areas due to uneven etching. Shallow etching clarifies the target and limits of this acid treatment, meaning that the etching depth is strictly limited to an extremely thin range. Its purpose is limited to removing the surface modification layer (hydrolysis layer) generated during the polishing process, rather than performing any deep material removal or morphological changes on the device body. Its function is only to clean the surface, not to process the surface.Etching the surface of the device under test with hydrofluoric acid for 10-15 minutes provides a quantitative and repeatable process window for shallow etching targets, ensuring sufficient removal of the hydrolyzed layer while preventing over-etching. Under a defined acid concentration (5%) and operating mode (static), etching time becomes the key variable controlling the removal depth. Setting a time range of 10-15 minutes is an empirical process window based on the balance between sufficient removal of the hydrolyzed layer and avoiding over-etching. This is sufficient for low-concentration hydrofluoric acid to fully react with the hydrolyzed layer of typical thickness, removing it essentially completely. At the same time, the relatively short time range and the control of concentration together constitute a safe process boundary, preventing the acid from continuing to cause significant and uncontrollable additional erosion to the subsurface crack tips or deformed layers that may have slightly higher chemical activity due to manufacturing defects after the hydrolyzed layer has been removed. This maximizes the protection of the morphology and state of the original subsurface damage to be tested from being altered by the acid etching process itself.

[0028] In this embodiment, after acid etching, the device under test (DUT) is rinsed with deionized water for 4-8 minutes and then rapidly dried with nitrogen to prevent water residue. By setting timed deionized water rinsing and rapid nitrogen drying, the etching reaction is terminated, acid residue is completely removed, and traceless drying is achieved. This eliminates any chemical residues and physical traces that may be introduced during the acid etching post-processing, ensuring that the surface of the DUT is restored and maintained in a clean, dry, and chemically neutral stable state, providing an interference-free reference surface for subsequent high-sensitivity optical performance testing (photothermal weak absorption, fluorescence testing). After acid etching, rinse the device under test with deionized water for 4-8 minutes. This thorough dilution and displacement completely terminates the chemical reaction and removes all soluble reaction products and acid residues, preventing secondary contamination or chemical reactions on the surface. Acid etching (especially hydrofluoric acid etching) is a chemical reaction process. After the reaction, reaction products (such as fluorosilicates, unreacted acid molecules, etc.) and other ions from the acid will adhere to the surface. Rinsing with deionized water utilizes its extremely high purity to avoid the formation of new contaminants or water stains on the device surface by impurities that may be present in ordinary water. Sufficient physical dilution and displacement, along with adequate rinsing time, ensures... Deionized water is thoroughly flowed over and wetted the entire surface of the component under test (especially the complex inclined structure of the magnetorheological pit). Through continuous water flow (or multiple water changes and soaking), the residual acid, reaction products and their ion concentrations are diluted to a negligible level, terminating any possible subsequent reactions (such as the slow erosion of the surface by residual acid). The thoroughness of rinsing is ensured. The longer rinsing time (compared to simple rinsing) is to overcome the liquid retention effect that may be caused by surface tension and the groove structure, and to ensure that the residue in the pit, the edges and other hard-to-reach areas are also effectively removed, thereby ensuring the consistency and cleanliness of the chemical state of the entire tested area, and establishing a uniform benchmark for subsequent tests. Even with thorough rinsing with deionized water, allowing the water to evaporate naturally on the component surface can cause the water film to shrink at the gas-liquid interface during evaporation. This can lead to localized concentration and deposition of any trace amounts of solutes that were not completely removed from the water, as well as particulate contaminants that fell from the air onto the wetted surface during rinsing. These contaminants can leave visible or invisible water stains, spots, or contamination films, which can severely affect subsequent optical testing. In photothermal weak absorption testing, any localized residues on the surface can become additional, non-intrinsic light absorption sources, generating false absorption signals and interfering with the judgment of the intrinsic absorption characteristics of the subsurface. In fluorescence testing, some residues may generate fluorescence themselves or quench fluorescence, introducing background noise or signal distortion.Nitrogen gas is used to rapidly dry the test element to prevent water residue, achieving rapid, non-contact, and residue-free physical drying. This completely eliminates the risk of water stains or trace contaminant accumulation on the surface due to natural evaporation. A high-speed, clean, and dry nitrogen gas flow physically disperses and removes the water film adhering to the surface before natural evaporation is complete. The rapid drying process is much faster than natural evaporation, shortening the time window for water film retention and contaminant accumulation. The airflow directly blows water away from the surface, rather than evaporating it, thus avoiding the process of solute localized concentration and deposition. High-purity nitrogen is chemically inert and dry, and will not introduce new contaminants. Rapid nitrogen drying is a non-contact drying method, avoiding scratches or fiber contamination that may occur with wiping. Optionally, after acid etching, the fused silica element is rinsed with deionized water for 5 minutes, and then rapidly dried with nitrogen gas to prevent water residue.

[0029] In this embodiment, the measurement of the inclined contour line of the magnetorheological pit in step S300 specifically involves: using a three-dimensional profilometer to perform one-dimensional measurement of the centerline contour of the magnetorheological pit to obtain positional information corresponding to different depths. By using a three-dimensional profilometer to perform one-dimensional measurement of the centerline contour of the magnetorheological pit, baseline geometric data characterizing the pit's depth variation can be obtained efficiently, accurately, and non-destructively. This provides a precise, continuous, and spatially traceable geometric reference baseline for subsequent optical performance scanning along the inclined contour line, thereby establishing a one-to-one correspondence and quantitative conversion relationship between the subsequently acquired optical performance signals and absolute depth coordinates. A 3D profilometer is used to achieve non-contact, high-resolution, and high-precision 3D topographic measurement, extracting precise 1D contour lines to provide data. The working principle of 3D profilometers (such as white light interferometers and confocal microscopes) is usually based on optical interferometry or confocal scanning, which can acquire 3D point cloud data of the surface under test in a non-contact and non-destructive manner, with micro-nano or even higher longitudinal and lateral resolution. Using a 3D profilometer, complete and detailed 3D topographic information of the entire magnetorheological pit region can be obtained, providing a rich and accurate data source for subsequent extraction of the contour of any specific path (such as the centerline). This ensures that the extracted contour lines can truly reflect the actual geometry of the pit, avoiding the risk of damage or contamination to the cleaned, fragile surface under test (especially the slope of the pit) caused by probe pressure or scratches, which is possible with contact measurements (such as probe profilometers). One-dimensional measurement of the centerline profile of the magnetorheological pit simplifies the data dimensions, focuses on core depth information, and obtains the most representative profile line, providing a precise moving path reference for subsequent point-to-point optical scanning. Selecting the centerline profile of the magnetorheological pit (usually the longitudinal profile line where the deepest point of the pit is located) for measurement can most directly and effectively reflect the continuous change in depth from the pit edge to the bottom of the pit, representing the ridge line of the pit and the typical path of the pit depth change. Using this as the path for subsequent optical scanning can most effectively explore the evolution of subsurface damage from the surface to the maximum removal depth, avoiding the problem of unrepresentative data that may be caused by selecting atypical paths. Extracting and focusing on the curve of height (depth) changing with horizontal position along the path of the centerline from the 3D topography data greatly simplifies the complexity of subsequent data association. In the subsequent step S400, the optical test probe (such as the laser focus point for photothermal and fluorescence testing) only needs to scan precisely along this known one-dimensional path (centerline). This is simpler and more efficient than the need to perform surface scanning on the entire 2D pit surface or random point selection testing. Furthermore, the data association (converting the horizontal coordinates of each test point to depth through this contour line) is more direct and accurate, providing a clear and unique coordinate mapping rule.Obtaining location information corresponding to different depths generates key lookup tables or functional relationships required for subsequent data association, thereby associating the test location with the subsurface depth. Through measurement with a 3D profilometer, the final data obtained is a dataset of the correspondence between the horizontal coordinates X and the corresponding longitudinal height (or depth relative to the original surface) Z of a series of discrete points (or continuous functions) along the pit centerline. This dataset (or the curve fitted by it) is the quantitative expression of the slope profile, establishing a precise mapping of spatial location. In step S400, when the optical testing system performs a test at a certain horizontal position Xi on the pit centerline, the system can immediately and uniquely determine the subsurface depth Zi corresponding to the test point by querying this profile data. The optical performance signal (such as absorption coefficient, fluorescence intensity) measured at point Xi is directly and quantitatively correlated with the depth Zi of the subsurface damage characterized by the signal, which is beneficial for realizing the subsurface damage performance distribution curve with depth (i.e., performance-depth profile).

[0030] In this embodiment, step S400 specifically involves: S401, performing a photothermal weak absorption test on the region where the magnetorheological pit is located on the surface of the component under test, obtaining the photothermal weak absorption change curve on the central contour line of the magnetorheological pit, and recording the horizontal distance at which the absorption rate peak disappears. l a S402. Along the central axis of the magnetorheological pit, select test areas sequentially from shallow to deep for fluorescence testing, and record the horizontal distance at which the fluorescence signal of the subsurface defect of the test element disappears. l f Two complementary optical tests are performed along a specific path (central axis), and the locations where specific signal characteristics disappear are recorded. The characteristic distributions of two physical signals directly related to laser damage performance as a function of depth are obtained, and quantifiable and definable subsurface damage boundary indices are extracted from them. From two independent dimensions of light energy absorption and defect emission, an objective and quantitative characterization of the subsurface damage layer depth and its performance degradation boundary is achieved, providing mutually verifiable performance criteria for the final determination of the damage layer depth. Based on the energy absorption dimension, the sensitivity distribution of the subsurface damage layer to laser energy is obtained, and the boundaries of its influence range are determined. The principle of photothermal weak absorption testing is to detect the slight temperature rise (or related thermal effect) of the material due to the absorption of light energy under laser irradiation. Subsurface damage regions (such as cracks, impurity doping, and amorphous layers) usually have a higher light absorption coefficient than the intact bulk material due to structural damage or the introduction of impurities. Scanning along the central axis of the magnetorheological pit (i.e., the path with continuously changing depth) yields a curve of absorptivity (or absorption signal intensity) versus horizontal position (corresponding depth). In areas with damage, the curve will show a peak or plateau higher than the background baseline. The horizontal distance at which the absorptivity peak disappears is recorded. l aAs the test point gradually moves from the damaged layer region into the intact bulk material region below, due to the low and uniform light absorption coefficient of the bulk material, the corresponding absorption signal will significantly decrease from a high value (peak) and tend towards a stable, low background value. The horizontal position corresponding to the disappearance of the peak marks the termination boundary of the abnormal light absorption effect caused by subsurface damage (a key performance directly related to laser-induced damage) along this path. The horizontal distance at which the absorption peak disappears is... l a The contour line established by S300 corresponds to a specific depth value, serving as a performance criterion for the depth of the damaged layer. Based on the defect energy level dimension, the distribution information of subsurface defects is independently acquired, and the boundaries of their existence range are determined. Fluorescence testing uses a specific wavelength laser to excite the material and detect its emitted fluorescence signal. Defects introduced by subsurface damage (such as oxygen vacancies, non-bridging oxygen hole centers, and metal impurity ions) will produce specific fluorescence emission peaks, the intensity of which is related to the defect concentration. The fluorescence signal of the intact fused silica body is very weak and has specific spectral characteristics. Testing along the central axis from shallow to deep conforms to the rule that the damaged layer usually decreases from the surface to the interior. The horizontal distance at which the defect fluorescence signal disappears is recorded. l f As the test point moves from the damaged layer towards the bulk material, the intensity of the characteristic fluorescence peak associated with the damage gradually decreases; when the test point penetrates into the undamaged bulk material, the characteristic fluorescence signal weakens to a level comparable to or indistinguishable from the background fluorescence level of the bulk material; the horizontal distance at which the defect fluorescence signal disappears corresponds to... l f This marks the distribution boundary of subsurface defects with specific fluorescence characteristics introduced by the manufacturing process along this path. The horizontal distance corresponding to the disappearance of the defect fluorescence signal can also be converted into a depth value through the contour line, which is a criterion for damage layer depth defined from the perspective of defect chemical and structural state. The two tests are synergistic and complementary, and through the measurement of two independent physical principles, they verify and complement each other to achieve a more comprehensive and reliable assessment of subsurface damage. The photothermal weak absorption test is mainly sensitive to defects that can effectively absorb laser energy and convert it into heat (such as cracks, certain metallic impurities), and is directly related to the thermal damage mechanism; the fluorescence test is sensitive to defects with specific energy level structures that can be excited to emit light (such as various point defects, color centers), and is related to the microstructure and chemical state of the defect; the two reflect damage from different physical levels (photothermal conversion and photo-photothermal conversion); recording two disappearance distances provides two boundary indicators that may be the same or different; the two can verify each other, if l a and l f Proximity enhances the reliability of damage depth determination; the two can complement each other. If differences exist (e.g., some defects have strong absorption but weak fluorescence, or vice versa), comprehensive analysis is necessary. la and l f It can more comprehensively reveal the complex composition and scope of influence of the damage layer, avoiding underestimation or misjudgment that may be caused by a single criterion.

[0031] In this embodiment, the photothermal weak absorption test in step S401 specifically involves: using a transmission mode, a test laser wavelength of 300nm-600nm, a power of 3W-8W, a step interval of 30μm-100μm, and scanning an area covering magnetorheological pits. Preferably, a transmission mode is used, with a test laser wavelength of 355nm, a power of 4W, a step interval of 50μm, and scanning an area covering magnetorheological pits. The transmission mode enables bulk material sensitivity detection of thermal effects caused by absorbed energy, making it particularly suitable for assessing subsurface and bulk defects in transparent or translucent materials. In transmission mode photothermal testing, the probe light (usually another low-power laser beam) passes through the sample under test. When the pump laser (such as a 355nm laser) irradiates the sample and is absorbed, generating heat, it causes local changes in the sample's refractive index and thermal expansion, thereby modulating the phase or intensity of the probe light. It is sensitive to the overall temperature rise or thermal gradient caused by absorption within the sample (including the subsurface), and can effectively detect defects distributed within a certain depth of the material that absorb laser energy and convert it into heat. Compared to the reflection mode, the transmission mode usually provides better sensitivity for bulk defect detection. The test laser wavelength is 355nm, which excites the unique absorption of fused silica material and its subsurface damage in the ultraviolet band, enhancing the signal-to-noise ratio of defect detection. The 355nm wavelength is located in the ultraviolet band, where fused silica material itself has an intrinsic absorption edge. Many subsurface defects introduced by manufacturing processes (such as grinding and polishing) (such as oxygen vacancy-related defects, non-bridging oxygen hole centers, impurities, etc.) will produce significantly enhanced absorption bands in the ultraviolet band. Using a 355nm laser as a pump source can efficiently excite the absorption of light energy by these defects, thereby generating a stronger photothermal signal. This results in a higher signal contrast (signal-to-noise ratio) between the defects and the intact material substrate, which is beneficial for more clearly identifying absorption rate peaks and thus more accurately determining their disappearance locations. The power is 4W, striking a balance between generating a sufficiently strong and stable photothermal signal and avoiding irreversible changes in the tested sample (especially at defects) caused by the test laser itself. The intensity of the photothermal signal is usually proportional to the pump laser power. The 4W power level provides a sufficiently high energy injection to ensure that even for defects with weak absorption, a temperature rise signal that can be clearly identified by the detection system can be generated. For fused silica materials and their subsurface damage, this power level is usually carefully controlled to be significantly below their laser-induced damage threshold, thereby ensuring that the testing process itself is non-destructive and will not change or even generate new defects due to the irradiation of the test laser during the detection process, thus ensuring the authenticity of the test results (i.e., reflecting the original subsurface damage state, rather than an artifact introduced by the test).A step size of 50 μm achieves an optimized match between spatial resolution and testing efficiency, ensuring effective differentiation of the distribution characteristics of subsurface damage while controlling overall testing time. The step size determines the density of data points along the scanning path (the central axis of the magnetorheological pit). A 50 μm interval is spatially sufficient to differentiate the scale of most subsurface cracks and damage areas introduced by conventional grinding and polishing processes, thus clearly depicting the fluctuations of the absorptivity curve and accurately capturing the peaks and their disappearance points. Too small a step size (e.g., less than 10 μm) will significantly increase the number of data points and testing time, but may have limited contribution to improving the accuracy of damage boundary determination. Too large a step size (e.g., greater than 200 μm) may miss some small-sized damage features or make the measured curve too smooth, resulting in blurred boundary positioning of peak disappearance. 50 μm is a typical value that balances sufficient resolution and reasonable testing efficiency in engineering practice. The scanning area covers the magnetorheological pit, ensuring complete detection of the entire depth variation region and acquiring a complete signal profile from the intact surface area, the damaged layer to the intact substrate. By ensuring that the scanning path (central axis) completely covers the entire range from the edge of the magnetorheological pit (corresponding to the original surface or very shallow layer) to the bottom of the pit (corresponding to the maximum exposure depth), a continuous signal curve can be obtained, starting from the area near the original surface where the damage is known to be undamaged or negligible, passing through the entire expected subsurface damage layer, and extending to the interior of the intact substrate material where the damage is confirmed to be undamaged. This complete coverage is a prerequisite for accurately determining when the signal peak appears, when it reaches its peak value, and when it finally disappears and returns to the background level. Without complete coverage, it is impossible to reliably determine the start and end boundaries of the damage, and thus impossible to accurately calculate la.

[0032] In this embodiment, the fluorescence test in step S402 specifically involves: a laser power of 40mW, a fluorescence imaging objective magnification of 20×, and a field of view of 120μm×120μm. By setting the excitation source power, microscopic magnification, and field of view, high spatial resolution and high signal-to-noise ratio excitation and collection of defect-induced fluorescence signals on the test area (magnetorheological pit slope) are achieved, ensuring that the detected fluorescence information precisely corresponds to a specific subsurface depth location in space. Within the limits allowed by the optical diffraction limit, with sufficient excitation intensity and spatial resolution, the fluorescence of microscopic defects related to subsurface damage is detected and located, providing a reliable microscopic detection basis for quantitatively determining the boundary of the damage layer in the defect luminescence dimension. A laser power of 40mW strikes a balance between effectively exciting defect fluorescence and avoiding signal saturation or photobleaching / photodamage, ensuring appropriate, stable, and repeatable fluorescence signal intensity. Within a certain power range, the intensity of the fluorescence signal is generally proportional to the excitation power. The 40mW laser power provides sufficient energy injection to excite the characteristic fluorescence of subsurface defects in fused silica (such as oxygen vacancies, non-bridging oxygen hole centers, and impurity ions), producing a fluorescence signal of moderate intensity that is easily captured by detection systems (such as CCDs or photomultiplier tubes), thus ensuring a good signal-to-noise ratio. This power level is set within a range that does not cause significant fluorescence saturation, photobleaching (attenuation of the fluorescence signal due to continuous irradiation), or additional photodamage to the sample. 40mW is a trade-off value designed to optimize excitation efficiency, signal stability, and measurement safety. A 20× fluorescence imaging objective provides moderate spatial resolution and working distance, enabling clear imaging and fluorescence collection of the inclined region (a non-ideal plane) of the magnetorheological pit. Objective magnification directly affects the spatial resolution, field of view, and working distance of the microscope system. A 20× objective provides micrometer-level optical resolution, facilitating the resolution and localization of microscopic defects associated with subsurface damage (such as microcracks and tiny impurity clusters). While higher magnifications (such as 50× or 100×) offer higher resolution, they typically come at the cost of reduced field of view and working distance. A 20× objective typically has a millimeter-level working distance; this longer working distance allows sufficient space at the front of the objective to approach and focus on the inclined surface of the pit without physical collision, facilitating continuous or point-by-point testing along the entire inclined profile. Choosing 20× magnification represents an engineering optimization between achieving micrometer-level resolution and maintaining sufficient field of view and working distance to meet the needs of inclined measurement.The field of view is 120μm × 120μm, defining a clear and precisely controllable detection area for each test point. This ensures the spatial positioning accuracy of fluorescence signal acquisition and matches the scanning strategy (along the central axis, from shallow to deep). Within the framework of step S400, fluorescence testing is performed by sequentially selecting test areas along the central axis of the magnetorheological pit, from shallow to deep. Each test area (i.e., each point) actually corresponds to a finite-area region centered on a point on the central axis. The 120μm × 120μm field of view clearly defines the actual sample area covered by each fluorescence imaging or spectral acquisition, ensuring that the fluorescence signal collected within this field of view can be uniquely identified. The image is correlated with the spatial location determined by step S300, corresponding to the center of the field of view, and further correlated with a specific depth. This provides a clear spatial sampling window for establishing a quantitative relationship between fluorescence signal intensity (feature) and spatial location (depth). Considering the width of the magnetorheological pit, a field of view width of 120 μm is sufficient to provide a representative sampling area near the central axis. At the same time, it ensures that when moving the test position along the central axis, there is a certain overlap between adjacent test fields of view to ensure continuity, while avoiding spatial information ambiguity due to an excessively large field of view. This is beneficial for accurately judging the trend of fluorescence signal change with position (depth) and accurately identifying the boundary where the signal disappears.

[0033] In this embodiment, step S500 specifically involves: when determining the depth of the subsurface damage layer of the device under test based on the horizontal distance of the subsurface damage extension and the inclined profile of the magnetorheological pit, comparing the horizontal distance at which the absorption rate peak disappears. l a The horizontal distance from the disappearance of fluorescence signals of subsurface defects l f Take the horizontal distance at which the subsurface defect disappears. l max =max( l a , l f Then, comparing the horizontal distance to the centerline profile of the magnetorheological pit... l max The corresponding depth h is the measured subsurface damage layer depth (SSD). By comparing and selecting the larger of the horizontal distances of the damage boundary determined by two independent performance tests, and mapping it to the final damage layer depth, a damage boundary covering the widest range of influence is determined from two key dimensions based on conservative and comprehensive evaluation principles. The quantitative indicators obtained in the preceding steps, reflecting different damage mechanisms, are integrated and transformed into a unique, clear, and engineering safety-oriented damage layer depth value, providing a direct, reliable, and relatively safe basis for the removal depth in post-processing. The horizontal distances at which the absorption rate peak disappear are compared. l aThe horizontal distance from the disappearance of fluorescence signals of subsurface defects l f Take the horizontal distance at which the subsurface defect disappears. l max =max( l a , l f Following the principle of least adverse or full coverage, the determined damage layer depth is ensured to cover all detected key defect types that have a potential negative impact on laser damage performance. The boundaries of photothermal weak absorption testing and fluorescence testing are based on two different physical criteria: energy absorption and defect presence. In actual subsurface damage layers, the distribution and influence range of different types of defects (such as cracks, impurities, and point defects) may not completely overlap. l a and l f There are three possible scenarios regarding the size relationship; l a ≈ l f This indicates that the damage boundaries of the two performance characteristics are basically consistent, and the influence range of the damage layer at the energy absorption and defect microstructure levels is similar. l a > l f This indicates that the energy absorption anomaly extends further than the specific fluorescence defect. This is due to the existence of certain defects with strong absorption but weak or no fluorescence (such as certain non-luminescent impurities or microcracks with specific orientations), or that the material at deeper depths, although lacking obvious fluorescence defects, has had its light absorption characteristics altered by residual stress, lattice distortion, etc. In this case, if only... l f Based on depth, this deep region with abnormal absorption characteristics will not be considered as a damaged layer that needs to be removed, but may become a potential damage hazard under subsequent high-power laser irradiation. l f > l a This indicates that specific fluorescence defects extend deeper than the macroscopic absorption anomaly. This is because there are certain point defects (such as deep-level defects) with low concentrations and small absorption cross-sections but characteristic fluorescence. Their fluorescence signals can be sensitively detected, but their absorption contribution is insufficient to form a significant peak on the photothermal test curve. In this case, if only... l a Based on depth, these deep point defect areas will not be removed, as they may be activated and accumulate under long-term or repeated high-power laser irradiation, eventually causing damage. (Maximum value will be used.) l max =max( l a ,l f To ensure the reliability of the assessment results and provide a relatively safe process guide for the subsequent manufacturing of high-damage-threshold components, a boundary that covers the most far-reaching impact of all the above possibilities needs to be adopted. That is, the final determined horizontal range of the damage layer should simultaneously cover all detectable defects with anomalous photothermal absorption and all detectable defects with characteristic fluorescence. This is equivalent to establishing a performance union criterion, ensuring that the final determined damage depth (SSD) is based on the furthest boundary revealed by two independent tests in both the energy absorption hazard and defect presence dimensions, thus theoretically eliminating the assessment risk of missing a potential damage source due to reliance on a single criterion. (Referring to the centerline profile of the magnetorheological crater, the horizontal distance...) l max The corresponding depth h is the measured subsurface damage layer depth SSD. This accurately converts the one-dimensional horizontal boundary position into a final, engineering-guided damage layer depth value, completing the conversion from signal location to process parameters. This is the final application of spatial coordinate mapping. The centerline profile of the magnetorheological pit has been accurately measured in step S300, essentially establishing a one-to-one correspondence between the horizontal coordinate X and the depth coordinate Z, Z=f(X). When the final horizontal boundary position is determined through comparison... l max Then, by querying or calculating the contour function, the corresponding unique and precise result can be obtained. l max The depth value h; this depth h is the maximum extension depth of the subsurface damage layer in the direction perpendicular to the component surface (SSD); this conversion process transforms the relative horizontal distance measured on the inclined plane based on optical performance testing into an absolute depth value perpendicular to the surface that can be directly used in engineering to guide subsequent polishing or etching removal processes. This is the final form of the output result of the entire evaluation method, thereby linking the detection evaluation with process decisions. The specific calculation method of step S500 is the final integration and output link of the evaluation logic of this invention. By introducing the comparison principle of taking the maximum value, it transforms two performance boundary indicators based on different physical principles ( l a , l f This is integrated into a comprehensive, relatively safe damage layer horizontal range. l max This not only reflects a scientific understanding of the complexity of subsurface damage (different types of defects may have different distribution characteristics), but also embodies the engineering conservatism principle for manufacturing high-reliability laser components, ensuring that the evaluation results cover all detected potential risk factors; finally, by... l maxMapped onto the precisely measured slope profile, the subsurface damage layer depth (SSD) with direct process guidance value was obtained. This completed the closed loop from multi-dimensional performance signal acquisition and analysis to a single, clear, and executable process depth parameter, enabling the output of the entire evaluation method (SSD) to be used directly, quantitatively, and reliably to guide subsequent processing, precisely control the amount of material removed, and thus optimize processing efficiency while ensuring effective damage elimination, thereby serving the precision manufacturing of high-damage-threshold fused silica high-intensity optical components.

[0034] In practice, a method for evaluating the subsurface damage performance of fused silica high-intensity optical elements is provided. The implementation steps include: cleaning the surface of the element under test; selecting two points on the surface of the element under test and performing magnetorheological polishing, utilizing the characteristic that magnetorheological polishing does not produce additional cracks to create pits (spots or bevels) on the surface of the element under test to expose the subsurface damage layer of the processed element; cleaning the surface of the element under test and performing acid etching to remove the hydrolysis layer caused by magnetorheological polishing; measuring the bevel contour line of the magnetorheological pit; performing photothermal weak absorption test and fluorescence test on the subsurface of the element under test from shallow to deep along the bevel contour line of the magnetorheological pit; determining the depth of the subsurface damage layer of the element based on the horizontal distance of the subsurface damage extension and the bevel contour of the magnetorheological pit. This invention has a simple process flow, strong operability, and can directly obtain subsurface damage information of the element, providing a direct processing basis for the manufacture of high-damage-threshold fused silica high-intensity optical elements.

[0035] Compared with the prior art, the subsurface damage performance evaluation method for fused silica high-intensity optical elements of the present invention has the following advantages: 1. The process of this invention is simple to operate and has high detection efficiency. This method utilizes magnetorheological polishing to create magnetorheological pits for subsurface damage detection. No additional damage is generated during this process, and the skill requirements for the operator are low. Simultaneously, magnetorheological polishing, with its unique shear removal mechanism, ensures a high removal rate of fused silica material, and the processing depth of the magnetorheological pits is controllable, thus improving detection efficiency.

[0036] 2. This invention offers high measurement accuracy. By introducing photothermal weak absorption testing and fluorescence testing, this method does not rely on microscopic detection or human visual damage assessment. It can directly obtain the damage performance characteristics of different depths of the subsurface of fused silica elements, thereby accurately determining the subsurface damage depth of the elements and providing direct processing basis for the manufacture of high-damage-threshold fused silica high-intensity optical elements.

[0037] like Figure 2As shown, this is the sample surface and magnetorheological pits after shallow etching with HF in an embodiment of the present invention. In the experiment, a magnetorheological polishing machine was used to create two polishing pits on the surface of the optical element under test. After polishing, a hydrolysis layer will be covered on the surface, which will cover the subsurface cracks. The sample can be shallowly etched with 5% hydrofluoric acid for 10-15 minutes to fully remove the polishing hydrolysis layer and expose the subsurface damage, which is beneficial for the observation of subsurface damage.

[0038] like Figure 3 As shown, this is the contour of the central axis of the magnetorheological pit in an embodiment of the present invention. After shallow etching with HF, a one-dimensional contour measurement of the pit on the surface of the sample to be tested is performed. A high-precision three-dimensional profilometer can be used to measure the central axis contour of the magnetorheological pit to obtain the position information corresponding to different depths.

[0039] like Figure 4 As shown, this is the photothermal absorption signal of the magnetorheological pit region on the surface in an embodiment of the present invention. Photothermal weak absorption analysis is performed on the magnetorheological pit region on the surface of the component under test. The scanning area covers the magnetorheological pit to obtain the laser damage performance at different depths of the component subsurface.

[0040] like Figure 5 The figure shows the evolution of the absorptivity along the central axis of the magnetorheological pit in an embodiment of the present invention. Figure 6 The image shows the evolution of fluorescence damage along the central axis of the magnetorheological pit in an embodiment of the present invention. Combined with... Figure 5 and Figure 6 The test results show that due to the clustering of cracks, such as Figure 6 As shown in (a), the surface absorption value of the component is unstable, and the surface absorption rate is generally very high, remaining on the order of hundreds of ppm. When the test depth along the central axis increases, the clustered cracks disappear, as... Figure 6 As shown in (b), the photothermal absorptivity drops sharply, reaching the substrate level. Subsurface cracks generated during the pre-processing of components are typically densely distributed in shallower regions. The crack density gradually decreases with increasing depth; beyond a certain depth, cracks become sporadic and their distribution varies across different regions. Even after the clustered cracks disappear, sporadic spikes still appear in the photothermal signal. Fluorescence detection identifies additional absorption caused not only by individual cracks but also by other defects, such as… Figure 6 (c) and Figure 6 As shown in (d), such isolated damage may be caused by uncontrollable vibrations, transient changes in the external environment, large abrasive particles, etc. When these sporadic peaks also disappear, the subsurface absorption characteristics of the sample are now consistent with the matrix material, and no damage is observed in the fluorescence test, such as... Figure 6 As shown in (e). Figure 5 The distance at which the absorption peak completely disappears and Figure 6The distance at which fluorescence damage completely disappears, along with the other two results, together determine the subsurface damage depth of the element.

[0041] Matters not covered in this invention are common knowledge.

[0042] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0043] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the subsurface damage performance of fused silica high-intensity optical elements, characterized in that, Includes the following steps: S100. Select points on the surface of the component under test, and use the characteristic of magnetorheological polishing that it does not produce additional cracks to create pits on the surface of the component under test in order to expose the subsurface damage layer of the component under test. S200, Acid etching is performed on the device under test to remove the hydrolytic layer formed on the surface of the device under test by magnetorheological polishing; S300, measuring the inclined profile of a magnetorheological pit; S400, along the inclined contour line of the magnetorheological pit, perform photothermal weak absorption test and fluorescence test on the subsurface of the element under test from shallow to deep; S500. Determine the depth of the subsurface damage layer of the device under test based on the horizontal distance of the subsurface damage extension and the inclined profile of the magnetorheological pit.

2. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 1, characterized in that, Before step S100, a step of cleaning the surface of the component under test is added, specifically: When cleaning the surface of the component under test, deionized water is used for ultrasonic cleaning; the ultrasonic cleaning temperature is controlled at 30℃, and the cleaning is performed sequentially at frequencies of 40KHz for 5 minutes, 80KHz for 5 minutes, 120KHz for 5 minutes, 160KHz for 5 minutes, 200KHz for 5 minutes, 240KHz for 5 minutes, and 270KHz for 5 minutes; after ultrasonic cleaning, nitrogen gas is used for drying.

3. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 1, characterized in that, The magnetorheological polishing in step S100 is specifically as follows: Two points were randomly selected on the surface of the component under test for magnetorheological polishing, resulting in two magnetorheological pits. The process parameters for magnetorheological polishing were: polishing wheel speed 120r / min-160r / min, flow rate 240L / min-280L / min, magnetic field current 6A-10A, and pressure depth 0.1mm-0.3mm.

4. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 1, characterized in that, Step S200 involves acid etching of the device under test, specifically as follows: When performing acid etching on the device under test, use 5% hydrofluoric acid to perform static shallow etching on the device under test. The surface of the device under test is etched with hydrofluoric acid for 10-15 minutes.

5. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 4, characterized in that, After acid etching, rinse the device under test with deionized water for 4-8 minutes, and then quickly dry the device under test with nitrogen to prevent water residue.

6. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 1, characterized in that, The measurement of the inclined profile of the magnetorheological pit in step S300 is specifically as follows: A three-dimensional profilometer was used to perform one-dimensional measurement of the centerline profile of the magnetorheological pit of the component, and the position information corresponding to different depths was obtained.

7. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 1, characterized in that, Step S400 is as follows: S401. Perform photothermal weak absorption tests on the region where the magnetorheological pit is located on the surface of the component under test, obtain the photothermal weak absorption change curve on the central contour line of the magnetorheological pit, and record the horizontal distance at which the absorption peak disappears. l a ; S402. Along the central axis of the magnetorheological pit, select test areas sequentially from shallow to deep for fluorescence testing, and record the horizontal distance at which the fluorescence signal of the subsurface defect of the component under test disappears. l f .

8. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 7, characterized in that, The photothermal weak absorption test in step S401 is as follows: The transmission mode was used, with a test laser wavelength of 355nm, a power of 4W, a step interval of 50μm, and the scanning area covering magnetorheological pits.

9. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 7, characterized in that, The fluorescence test in step S402 is as follows: The laser power is 40mW, the fluorescence imaging objective has a magnification of 20×, and the field of view is 120μm×120μm.

10. The method for evaluating the subsurface damage performance of fused silica high-intensity optical elements according to claim 1, characterized in that, Step S500 is as follows: When determining the depth of the subsurface damage layer of the device under test (DUT) based on the horizontal distance of the subsurface damage extension and the inclined profile of the magnetorheological crater, the horizontal distance at which the absorption rate peak disappears is compared. l a The horizontal distance from the disappearance of fluorescence signals of subsurface defects l f Take the horizontal distance at which the subsurface defect disappears. l max =max( l a , l f ); Then, comparing the horizontal distance to the centerline profile of the magnetorheological pit... l max corresponding depth h This is the measured subsurface damage layer depth (SSD).

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