Laser damage threshold analysis method

Abstract

The present invention belongs to the field of laser damage analysis technology, and in particular relates to a laser damage threshold analysis method. The method comprises: S1: establishing a hypervelocity impact finite element model based on finite element simulation software; S2: performing a hypervelocity impact simulation based on the established hypervelocity impact finite element model to obtain a target model after the impact, and extracting three-dimensional morphological data of the impact crater from the target model after the impact; S3: establishing an optical element model, importing the three-dimensional morphological data of the impact crater into multi-physics field coupling calculation software, and fitting the three-dimensional morphological data and the optical element model to obtain a model of the optical element after the impact, and using pulsed laser and the optical element model after the impact to obtain the laser damage threshold; S4: selecting the film layer and mirror material of the optical element. The present invention analyzes and studies the laser damage threshold, which has a guiding role in the selection of materials for space telescopes.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser damage analysis, and in particular relates to a laser damage threshold analysis method. Background Art

[0002] In the complex space environment, the performance stability and service life of optical components used in laser systems can be significantly affected by external environmental factors. Therefore, the numerous micrometeoroids and space debris pose a significant threat to the service life and imaging quality of optical components. This is especially true for laser systems, where high-power lasers can cause difficult-to-quantify damage due to tiny defects.

[0003] In the space environment, there are many factors that affect the damage threshold of optical components, such as high vacuum environment, high and low temperature cycles (-80℃~120℃), solar ultraviolet radiation, charged particles and micrometeorites, etc. This paper focuses on the impact of micrometeorites and space debris. In the space environment, micrometeorites and space debris with a size less than 1mm are small particles in space. Space debris is usually some aluminum alloys and metal oxides such as zinc and titanium, with a density of 2.8 The average impact velocity of a micrometeoroid is 10 km / s, while the average impact velocity of a micrometeoroid can reach up to 20 km / s. These numerous tiny particles pose a significant threat to spacecraft on mission. Optical payloads such as space telescopes onboard spacecraft are inevitably exposed to harsh environments, subject not only to impacts from micrometeoroids but also to extremely strong ultraviolet and cosmic rays. For example, the James Webb Telescope has been struck by a micrometeoroid. Although researchers simulated this with small samples before launch, similar impacts are unavoidable. Impacts inevitably result in mirror defects or the accumulation of microscopic contaminants. These defects and microscopic contaminants alter light absorption, leading to localized temperature increases in optical components, damage to the optical component morphology, and a reduction in the laser-induced damage threshold. Furthermore, they can damage optical coatings and mirrors, reducing the lifespan of the space telescope. Therefore, at present, in order to deal with the damage caused by ultra-high-speed impacts of tiny particles such as micrometeoroids and space debris on space optical components, there is an urgent need to invent a method for analyzing and simulating the impact of the light field distribution on the damaged space optical components, as well as a method for analyzing and simulating the laser damage threshold on the surface of the damaged space optical components. Summary of the Invention

[0004] In view of this, the present invention aims to provide a laser damage threshold analysis method to solve the problem that the existing technology lacks a method for analyzing and simulating the damage caused by ultra-high-speed impacts of tiny particles such as micrometeoroids and space debris on space optical components. The present invention uses multi-physics field coupling technology to study the laser damage threshold problem caused by defect damage after the impact, which is of great significance to the selection of space telescope materials and the preparation of protective measures.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A laser damage threshold analysis method is used to perform laser damage threshold analysis on the surface of an optical component after a hypervelocity impact, specifically comprising the following steps:

[0007] S1: Establish a hypervelocity impact finite element model based on finite element simulation software. The hypervelocity impact finite element model includes an impactor model and a target model.

[0008] S2: Setting the equation of state and failure model for the hypervelocity impact finite element model, and performing a hypervelocity impact simulation based on the set hypervelocity impact finite element model to obtain a target model after the impact, and extracting the three-dimensional morphology data of the impact crater from the target model after the impact;

[0009] S3: Build an optical component model, import the 3D morphology data of the impact crater into multi-physics field coupling calculation software, and fit the 3D morphology data and the optical component model to obtain the optical component model after the impact. Use the pulsed laser and the optical component model after the impact to obtain the laser damage threshold;

[0010] S4: Select the coating and mirror materials of optical components based on laser damage threshold and laser ablation rate.

[0011] Furthermore, the physical properties of the impactor include shape, density, size, impact velocity and impact angle, and the physical properties of the target include density, specific heat capacity, melting point, maximum principal stress, shear modulus, Poisson's ratio, static yield limit and strain hardening modulus.

[0012] Furthermore, in step S1, the impactor includes micrometeoroids and space debris, and the density of micrometeoroids is in the range of 0.16g / -4g / Between, the size range is 0.5 -1cm, the density of space debris is 2.7 ;

[0013] The density of micrometeoroids ranges from 0.16 g / to 4g / The density-mass relationship of micrometeoroids is:

[0014] ;

[0015] Where m represents the mass of the micrometeoroid in g. is the density.

[0016] Furthermore, the target body includes a mirror surface and an optical film coated on the mirror surface, and the thickness of the mirror surface is at least five times the length of the impactor.

[0017] Furthermore, in step S2, the 3D morphology data of the impact crater is extracted using the built-in algorithm of LS-prepost to obtain the crater depth and defect diameter of the target body;

[0018] The calculation formula of the target pit depth is:

[0019] ;

[0020] in, Because the pit is deep, is the impactor diameter, is the impactor density, is the impactor velocity, is the target density, is the target yield strength;

[0021] The defect diameter of the target is:

[0022] ;

[0023] in, is the defect diameter.

[0024] Furthermore, in step S3, the structure of the optical element model is consistent with that of the target model in step S1.

[0025] Furthermore, in step S3, the specific steps of obtaining the laser damage threshold using the pulsed laser and the optical element model after being impacted include:

[0026] S31: Set a pulse laser above the defect of the optical component model after impact. The pulse time interval of the pulse laser is s, the laser function of the pulsed laser is a Gaussian function, and the ramp function and heat transfer coefficient function are inserted into the multi-physics field coupling calculation software;

[0027] S32: Using multi-physics field coupling calculation software, the initial temperature is set to room temperature (300K), and the laser damage caused by the pulsed laser irradiation power to the optical component model after the impact is simulated to obtain the laser damage threshold of the optical component model after the impact of the current material;

[0028] S33: Replace the mirror material of the target body, repeat steps S1-S32, and obtain the laser damage threshold of the optical element model after being impacted by different materials.

[0029] Furthermore, step S4 specifically includes the following steps:

[0030] S41: ablating the impacted optical component models of different materials using a pulsed laser, and calculating the laser ablation rates of the impacted optical component models of different materials based on the ablation times taken for the impacted optical component models of different materials to reach the same ablation depth;

[0031] S42: Using the pulsed laser of step S31, laser ablation simulation is performed on intact optical component models of different materials to obtain laser damage thresholds of the intact optical component models of different materials;

[0032] S43: Repeat step S41 using intact optical component models made of different materials to calculate the laser ablation rate of the pulsed laser on the intact optical component models made of different materials;

[0033] S44: Calculate the percentage of the laser damage threshold of the intact optical component model of different materials and the laser damage threshold of the optical component model of the corresponding material after impact, and select the film layer and mirror material of the optical component based on the laser ablation rate of the pulsed laser on the intact optical component model and the optical component model after impact.

[0034] Furthermore, the intact optical element model is the optical element model that is not fitted with the three-dimensional shape data in step S3.

[0035] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0036] This invention proposes a laser damage threshold analysis method for optical component surfaces based on hypervelocity impacts. Using FEM-SPH finite element simulation technology to simulate hypervelocity impacts between micrometeoroids and space debris, and employing multi-physics coupling techniques, this method investigates the laser damage threshold caused by post-impact defect damage. This method focuses on post-damage simulation technology for defects and is of great significance for the selection of materials for space telescopes and the preparation of protective measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0038] Figure 1A schematic diagram of a simulation process for obtaining the laser damage threshold of an optical element according to an embodiment of the present invention;

[0039] Figure 2 A schematic flow chart of the laser damage threshold analysis method according to an embodiment of the present invention;

[0040] Figure 3 Schematic diagram of the FEM-SPH theory described in the embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of laser damage simulation according to an embodiment of the present invention;

[0042] Figure 5 A finite element model diagram of a hypervelocity impact according to an embodiment of the present invention;

[0043] Figure 6 The impact effect diagram described in the embodiment of the present invention is created;

[0044] Figure 7 This is a diagram of the laser 3D damage effect described in the embodiment of the present invention;

[0045] Figure 8 This is a schematic diagram of the isotherms described in the embodiment of the present invention;

[0046] Figure 9 A schematic diagram of the grid skewness described in an embodiment of the present invention.

[0047] Description of reference numerals:

[0048] 1. Pulsed laser; 2. Glass; 3. Plasma ball; 4. Damage crater; 5. Impactor; 6. Target; 7. Impact area; 8. Stress wave; 9. Debris cloud. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0050] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0051] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0052] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0053] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0054] like Figure 1As shown, in order to explore the damage caused by tiny particles in space to optical components and the impact of their laser damage, the present invention proposes an analysis method for the laser damage threshold of tiny particles impacting the surface of optical components at high speed based on finite element simulation: first, the hypervelocity impact process is modeled. During the modeling process, the damage morphology is first estimated. The laser damage thresholds corresponding to the three damage conditions are different. Taking pit opening as an example, the physical parameters are imported into the established hypervelocity impact model. Since the transient pressure of the impact is huge, the state equation is supplemented in the hypervelocity impact model. During the simulation process, the Grüneisen and Tillotson equations are compared. According to the comparison results, the state equation adopts the more appropriate Grüneisen model. Finally, a failure model is added. The failure model mainly adopts the FEM-SPH adaptive grid method. At this point, the simulation of the hypervelocity impact is completed, and the three-dimensional damage morphology of the impact damage is obtained (derived by LS-Prepost). The three-dimensional damage morphology is then imported into the multi-physics coupling calculation software for analysis, mirror fitting, and laser ablation simulation is performed. The key step in the laser ablation simulation is to set the grid gradient (adding a ramp function and heat transfer coefficient) to make the laser ablation conform to the actual situation, thus completing the laser damage study. Finally, data analysis is performed. The first intuitive step is to obtain the three-dimensional damage morphology of the optical element. The simulation time is then derived from the multi-physics coupling calculation software. The laser ablation rate of optical elements of different materials is compared. Finally, a scattering analysis of the laser damage is performed (scattering analysis is closely related to the process of determining the laser damage threshold. After the optical element is impacted, there will be impact craters of varying depths on the surface. Different impact craters scatter the laser, thereby determining the scattering of the laser damage. Those skilled in the art believe that obtaining the laser damage threshold of the optical element after the impact can determine the scattering analysis results of the laser damage. Therefore, the present invention does not elaborate on scattering analysis) to determine the impact of defect scattering. The use of the optical element is evaluated based on the damage condition, ablation rate, and scattering condition to complete the laser damage threshold analysis.

[0055] like Figure 2As shown, the present invention provides a laser damage threshold analysis method for performing laser damage threshold analysis on the surface of an optical element after a hypervelocity impact, specifically comprising the following steps: S1: establishing a hypervelocity impact finite element model based on finite element simulation software, the hypervelocity impact finite element model including an impactor 5 model and a target body 6 model; S2: setting a state equation and a failure model for the hypervelocity impact finite element model, and performing a hypervelocity impact simulation based on the set hypervelocity impact finite element model to obtain a target body 6 model after the impact, and extracting three-dimensional morphology data of the impact crater from the target body 6 model after the impact; S3: establishing an optical element model, importing the three-dimensional morphology data of the impact crater into multi-physics field coupling calculation software, and fitting the three-dimensional morphology data and the optical element model to obtain a model of the optical element after the impact, and obtaining the laser damage threshold using a pulsed laser 1 and the optical element model after the impact; S4: selecting the film layer and mirror material of the optical element based on the laser damage threshold and the laser ablation rate.

[0056] It should be noted that the equation of state and failure model in step S2 are modules within the ANSYS software. Hypervelocity impact simulation is performed in ANSYS's LS-DYNA software. The selection of the equation of state is primarily based on the material properties and the specific effects of material deformation (such as vaporization) under hypervelocity impact. Currently, the main equations of state are the Tillotson equation of state and the Grüneisen equation of state. The Tillotson equation of state is suitable for describing the state changes of materials such as metals under high pressure and is particularly well-suited for numerical simulation of hypervelocity impacts. Examples include Be metal and Al alloys. The Grüneisen equation of state is relatively simple in its basic form, typically consisting of equations relating pressure, volume, and energy. It is primarily used to describe the state changes of solid materials and is particularly widely used in explosion and shock wave simulations. It is applicable to ceramics such as SiC, ultra-low expansion quartz glass (ULE), glass-ceramics (Zerodur), and carbon fiber composites. The selection of the equation of state should be tailored to the specific material of the optical element (target plate). The failure model is the maximum principal stress that the optical element (target plate) can withstand. When the optical element (target plate) is subjected to the maximum principal stress of the material, deformation and breakage will occur.

[0057] In some embodiments, the physical properties of the impactor 5 include shape, density, size, impact velocity and impact angle, and the physical properties of the target 6 include density, specific heat capacity, melting point, maximum principal stress, shear modulus, Poisson's ratio, static yield limit and strain hardening modulus.

[0058] It should be noted that the specific steps of step S1 include: using CAD or other software to establish a geometric model of the impactor 5 and a geometric model of the target 6; setting the physical properties of the impactor 5 and the physical properties of the target 6 in LS-DYNA software; importing the geometric models of the impactor 5 and the geometric models of the target 6 into LS-DYNA software to match the geometric models of the impactor 5 with the physical properties, and also to match the geometric models of the target 6 with the physical properties; setting the calculation time, velocity of the impactor 5, and mesh size of the hypervelocity impact finite element model in LS-DYNA software; based on the above settings, LS-DYNA software automatically fills data into the hypervelocity impact finite element model; and importing the automatically filled data of the hypervelocity impact finite element model into LS-Prepost software for data improvement (adjustment based on actual needs) to obtain the hypervelocity impact finite element model.

[0059] In some embodiments, in step S1, the impactor 5 includes micrometeoroids and space debris, and the density of the micrometeoroids is in the range of 0.16 g / -4g / Between, the size range is 0.5 -1cm, the density of space debris is 2.7 ;

[0060] The density of micrometeoroids ranges from 0.16 g / to 4g / The density-mass relationship of micrometeoroids is:

[0061] ;

[0062] Where m represents the mass of the micrometeoroid in g. is the density.

[0063] It should be noted that the present invention investigates the size of micrometeoroids and space debris. Space debris is mainly composed of failed aerospace components, with a density close to that of aluminum, which is 2.7 The density of micrometeoroids is uncertain. According to radar observation, the density of micrometeoroids is 0.16g / to 4g / The specific density-mass relationship between them is:

[0064] ;

[0065] Where m represents the mass of the micrometeoroid in g. The main object of this invention is the tiny particles whose size cannot be numbered (less than 1 cm) but will affect the optical elements. Specifically, the particle size range of this invention is 0.5 -1mm. The flight speed of space debris is usually around 10km / s, and can reach up to 15km / s. The flight speed of micrometeoroids has a wide range, with a speed relative to the earth of 11-72km / s and an average speed of about 20km / s. Due to the limitations of experimental conditions, the present invention focuses on tiny particles with a speed of 1km / s-10km / s. The impact pressure generated by solid materials during hypervelocity collisions is much greater than their yield strength. Therefore, in the initial stage of such collision processes, the morphology of the colliding solid is similar to that of a compressible fluid, that is, both the impactor 5 and the target 6 will exhibit a flow state. Therefore, in the simulation response, the fluid mechanics properties of the material need to be considered. During a hypervelocity collision, due to the high collision speed and the high transient pressure of the collision, the material will produce phenomena that are impossible to occur under low-speed collisions, such as melting and vaporization. Therefore, the factors that affect the cratering of the target body 6 are: (1) Geometric factors: the size and shape of the impactor 5 and the target body 6 (the size of the target body 6 is five times the size of the impactor 5, and the thickness of the target body 6 is five times the diameter of the impactor 5); (2) The collision factors, impact angle, speed and pressure parameters of the impactor 5 and the target body 6 (the projectile velocity, the impact angle ... , impact angle ); (3) Material physical factors, such as the density, modulus, strength, temperature, sound velocity and specific heat of the impactor 5 and the target 6 (the density of the impactor 5 is , the density of target 6 is , the modulus of impactor 5 is , the modulus of target 6 is , the strength of impactor 5 is , the modulus of target 6 is , the modulus of impactor 5 is , the modulus of target 6 is ).

[0066] Based on the above parameters, the target body 6 has a crater diameter of for:

[0067] ;

[0068] in, The diameter of the impactor 5.

[0069] The depth of the target 6 Expressed as:

[0070] ;

[0071] Use the dimensional method to simplify the above two equations:

[0072] ; ;

[0073] When the geometry of the simulated target is the same as that of the original target (impactor 5 and target body 6), and the impact posture is also the same, eliminating similar terms yields:

[0074] ;

[0075] After summarizing the experimental laws and empirical formulas, the classic "2 / 3 law" was derived:

[0076] ;

[0077] In the thin plate perforation experiment, considering the influence of inertia and material strength, the aperture expression obtained by fitting is:

[0078] ;

[0079] After deriving these two formulas, we obtain the expressions for the defect pit depth and defect radius of hypervelocity impact.

[0080] In some embodiments, the target 6 includes a mirror surface and an optical film coated on the mirror surface, and the thickness of the mirror surface is at least five times the length of the impactor 5 .

[0081] In some embodiments, in step S2, the LS-prepost built-in algorithm is used to extract the three-dimensional morphology data of the impact crater to obtain the crater depth and defect diameter of the target body 6;

[0082] The calculation formula of the pit depth of the target body 6 is:

[0083] ;

[0084] in, Because the pit is deep, is the diameter of the impactor, is the density of the impactor 5, For the impactor 5 speed, is the density of target 6, is the yield strength of target 6;

[0085] The defect diameter of target 6 is:

[0086] ;

[0087] in, is the defect diameter.

[0088] In step S2, the density of the impactor 5 and the target 6 is kept constant, and the impact speed is changed to form different impact craters. The speed range of the impactor 5 is 1 km / s - 10 km / s, with a step size of 1 km / s; the size and density of the target 6 are kept constant, the geometric diameter of the impactor 5 is changed, and the same speed is maintained to observe the morphology of the impact crater; the size and speed of the target 6 are kept constant, the density of the impact material is changed, and the size of the impact damage is studied. The density of the impactor 5 is set to: 0.5g / , 1g / , 0.9 g / , 2g / , 2.8g / Then, a comparison table of various indicators of impact object 5 and the morphology of the impact crater is obtained.

[0089] Next, set the failure model. Setting the failure model mainly involves dividing the FEM-SPH adaptive grid. The failure value is that the hexahedral grid deformation exceeds 1 and is converted into SPH particles. The state equation is added using the keyword module in LS-Prepost. The calculation time is set according to the flight speed of the impactor 5 and the thickness of the target 6. Generally, it is set to one microsecond. SPH particles have been added when setting the FEM-SPH adaptive grid. This is mainly based on the limitation of computer performance. Here, one SPH particle is set for one hexahedral unit, such as Figure 3 As shown, the SPH particle smoothing length constant is generally filled in automatically by the system, and the setting of the maximum principal stress is mainly set according to the mirror material through the keyword module.

[0090] Then the laser damage analysis is performed on the damage defects (including defect pit depth and defect radius). Figure 4 The laser damage simulation process of the defective reflector is also the same as Figure 4 Similarly, the mirror structure is first irradiated with a laser, causing the surface of the glass 2 (target 6) to begin to melt. Then, irradiation is added to heat conduction, causing the material on the surface of the glass 2 (target 6) to vaporize. Under continuous energy input and material changes, a plasma ball 3 is formed. After the irradiation is completed, a damage pit 4 appears on the mirror structure (target 6).

[0091] In some embodiments, in step S3 , the structure of the optical element model is consistent with the structure of the target 6 model in step S1 .

[0092] In some embodiments, in step S3, the specific steps of obtaining the laser damage threshold using the pulsed laser 1 and the optical element model after being impacted include:

[0093] S31: Set pulse laser 1 above the defect of the optical element model after impact, and the pulse time interval of pulse laser 1 is s, the laser function of pulse laser 1 is a Gaussian function, and the ramp function and heat transfer coefficient are inserted into the multi-physics field coupling calculation software;

[0094] S32: Using multi-physics field coupling calculation software, the initial temperature is set to room temperature (300K), and the laser damage caused by the irradiation power of pulse laser 1 to the optical element model after the impact is simulated to obtain the laser damage threshold of the optical element model after the impact of the current material;

[0095] S33: Replace the mirror material of the target 6, and repeat steps S1-S32 to obtain the laser damage threshold of the optical element model after being impacted by different materials.

[0096] It should be noted that the ramp function y is y=10 6 x, the heat transfer coefficient is y×(TT a ), where x is the pit depth, T is the initial temperature (room temperature), and T a is the ablation temperature.

[0097] Furthermore, let the absorption coefficient of the optical film be , the energy density of the incident laser is , after passing through a distance of thickness d, the light intensity will drop to:

[0098] ;

[0099] Where R is the reflectivity of the optical film surface.

[0100] Let C be the heat capacity of the optical film, is the material density, M is the relative molecular mass, and the surface temperature rise caused by intrinsic absorption after laser irradiation is approximately:

[0101] ;

[0102] When the surface temperature of an optical film rises and exceeds the critical damage temperature, the optical film will be damaged. This temperature is the thermal stress failure temperature or the melting point of the optical material.

[0103] The present invention focuses on the change of laser damage threshold caused by defects. Therefore, more consideration should be given to impurity absorption. Assuming that the impurity shape is spherical, such as Figure 5 As shown in Figure 2, the splashing SPH particles are also spherical. Compared with the impurity absorption, the matrix absorption can be ignored. The corresponding heat conduction equation is:

[0104] ;

[0105] ;

[0106] ;

[0107] Where T is the temperature, the subscripts i and h represent the impurity and the matrix respectively, x and k are the diffusion coefficient and thermal conductivity respectively, a is the radius of the impurity (ball), and q is the heat source term. Since the present invention assumes that the absorbing impurity is spherical, the absorption cross section is ,but:

[0108] ;

[0109] Where t is the pulse width of the incident laser. When the light absorption length is greater than the defect length, the energy deposition inside the defect can be considered uniform. If the impurity is in close contact with the matrix, then:

[0110] ;

[0111] ;

[0112] Therefore, the exact solution of the impurity heat conduction equation is:

[0113] ;

[0114] in,

[0115] ;

[0116] When laser irradiated, the temperature at the defect increases, the absorption increases, and the reflection coefficient R decreases. The relationship between the reflection coefficient R and temperature can be expressed as:

[0117] ;

[0118] in, is the nonlinear coefficient, when =0, the model becomes a linear absorption model. represents the reflection coefficient at the surface defect of the film on the right side of the initial laser. When the temperature rises to the melting point of the film and the reflector, the impact area 7 is visible, indicating the effect of laser damage. The derivation here mainly serves to supplement the explanation of the possible changes in reflectivity caused by temperature changes in optical components made of different materials during laser ablation, and the impact of temperature changes on light absorption (i.e., laser ablation).

[0119] In some embodiments, step S4 specifically includes the following steps:

[0120] S41: ablating the impacted optical component models of different materials using the pulsed laser 1, and calculating the laser ablation rates of the impacted optical component models of different materials using the pulsed laser 1 based on the ablation times taken for the impacted optical component models of different materials to reach the same ablation depth;

[0121] S42: Using the pulsed laser 1 of step S31, laser ablation simulation is performed on intact optical component models of different materials to obtain laser damage thresholds of the intact optical component models of different materials;

[0122] S43: Repeat step S41 using intact optical component models of different materials to calculate the laser ablation rate of the pulsed laser 1 on the intact optical component models of different materials;

[0123] S44: Calculate the percentage of the laser damage threshold of the intact optical component model of different materials and the laser damage threshold of the optical component model of the corresponding material after being impacted, and select the film layer and mirror material of the optical component based on the laser ablation rate of the pulse laser 1 on the intact optical component model and the optical component model after being impacted.

[0124] It should be noted that an optical element with a low ablation rate and a small percentage value is selected.

[0125] In some embodiments, the complete optical element model is the optical element model that is not fitted with the three-dimensional topography data in step S3.

[0126] The optical element is irradiated with a pulsed laser 1, and the irradiation power is increased according to a preset step size. The boundary probe can detect the time taken for mirrors of different materials to reach the same ablation depth. Comparing the irradiation power can more intuitively reflect the laser ablation rate. Irradiation power that does not reach damage cannot produce laser damage. For the selection of reflector and film layer data, most of the research materials targeted by the present invention are optical elements used in aerospace and other fields. After the geometric model is established, different parameters are adjusted to obtain the most suitable optical element material, such as: the density of the mirror, the thickness of the optical film, and the refractive index coefficient of the film layer of the optical film. The ablation time is the pulse time interval of the pulsed laser 1. s multiplied by the number of shots of pulse laser 1.

[0127] like Figure 6 As shown, the three-dimensional coordinates represent the size of the optical element model, and the temperature scale is on the right. The stress wave 8 and the debris cloud 9 are shown in the figure. Figure 7 The damage morphology of laser damage is intuitively shown.

[0128] like Figure 8 As shown, the time in the upper left corner represents the time required for ablation to the current depth. The Y-axis and X-axis in the figure represent the size of the ablation and the size of the optical element respectively. The right side represents the temperature. The isotherms in the figure have colors before grayscale, indicating that the temperature near the ablation pit is higher, which also represents the heat transfer ability of the optical element model.

[0129] like Figure 9 As shown, the coordinate axis is schematically shown in Figure 8 Same as above, with the skewness scale on the right. This is the effect after adding the slope equation and refining the grid. Figure 9 It mainly demonstrates the grid changes of laser ablation and the role of ramp function.

[0130] The present invention is primarily implemented through simulation, so the damage situation can be intuitively represented in the simulation results. Furthermore, the simulation results include a value called laser damage time, which is primarily based on a comparison of the time it takes for an intact mirror to be laser damaged to a certain depth and the time it takes for it to be laser damaged again after being damaged by hypervelocity impact. These two values ​​are then expressed as percentages and tabulated based on the different optical materials to compare the damage situations. The service life is also evaluated based on the time parameter, and scattering analysis is incorporated into the data analysis to assess the impact of damage morphology on optical components.

[0131] The laser damage threshold (LDT) refers to the maximum laser energy density or power density that a material or optical component can withstand without permanent damage under specific laser parameters (such as wavelength, pulse width, and repetition rate). Exceeding this threshold causes irreversible damage to the material, such as melting, ablation, and coating loss. This study primarily examines the impact of physical damage to optical components, such as space telescopes, from tiny particles like space debris or micrometeoroids. The assessment process primarily compares the LDT of an intact optical component with the percentage of the LDT after impact. If the pit depth exceeds the thickness of the optical film, damage to the mirror itself is present. This involves comparing the LDT of the mirror with the LDT after impact. Different optical materials (optical films and mirrors) have different LDTs, which is why percentages are compared. The pit depth indicates the depth of the impact and has a direct impact on laser damage. For example, an impact crater can focus light, increasing absorbed energy. The defect diameter affects the area of ​​light (energy) absorption.

[0132] This study investigates the physical damage caused by impact, specifically the maximum pit depth and maximum defect radius of hypervelocity impact. These two parameters are combined to extract the defect damage morphology, which is then fitted onto a reflector for laser damage analysis. The goal is to investigate the impact of small defects on laser damage, with the primary metric being the time it takes for the film and reflector to reach their melting points—the laser damage time. Based on this study of hypervelocity impact, the post-damage effects of small defects are analyzed, primarily using finite element simulation techniques to address the difficult challenges of quantifying damage and lifetime assessment.

[0133] In summary, this method can be used to analyze damage caused by ultrahigh-velocity particle impacts on optical components in complex space environments. It also investigates the post-damage behavior of defects—the effects of laser damage. This method uses finite element simulation to analyze laser damage to defects. This method provides data support for the protection of space telescopes and the assessment of the service life of optical components. It also provides guidance for the development of new materials for coatings and reflectors, as well as for the improvement of existing materials.

[0134] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0135] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A laser damage threshold analysis method for performing laser damage threshold analysis on the surface of an optical component after a hypervelocity impact, characterized by: The specific steps include: S1: Establish a hypervelocity impact finite element model based on finite element simulation software. The hypervelocity impact finite element model includes an impactor model and a target model. S2: Setting the equation of state and failure model for the hypervelocity impact finite element model, and performing a hypervelocity impact simulation based on the set hypervelocity impact finite element model to obtain a target model after the impact, and extracting the three-dimensional morphology data of the impact crater from the target model after the impact; S3: Build an optical component model, import the 3D morphology data of the impact crater into multi-physics field coupling calculation software, and fit the 3D morphology data and the optical component model to obtain the optical component model after the impact. Use the pulsed laser and the optical component model after the impact to obtain the laser damage threshold; In step S3, the specific steps of obtaining the laser damage threshold using the pulsed laser and the optical element model after being impacted include: S31: Setting a pulse laser above the defect of the optical element model after the impact, wherein the pulse time interval of the pulse laser is s, the laser function of the pulsed laser is a Gaussian function, and a ramp function and a heat transfer coefficient function are inserted into the multi-physics field coupling calculation software; S32: Using multi-physics field coupling calculation software, the initial temperature is set to room temperature (300K), and the laser damage caused by the pulsed laser irradiation power to the optical component model after the impact is simulated to obtain the laser damage threshold of the optical component model after the impact of the current material; S33: replacing the mirror material of the target body, repeating steps S1-S32, and obtaining the laser damage threshold of the optical element model after being impacted by different materials; S4: Select the coating and mirror materials of optical components based on laser damage threshold and laser ablation rate; Step S4 specifically includes the following steps: S41: ablating the impacted optical component models of different materials using a pulsed laser, and calculating the laser ablation rates of the impacted optical component models of different materials based on the ablation times taken for the impacted optical component models of different materials to reach the same ablation depth; S42: Using the pulsed laser of step S31, laser ablation simulation is performed on intact optical component models of different materials to obtain laser damage thresholds of the intact optical component models of different materials; S43: Repeat step S41 using intact optical component models made of different materials to calculate the laser ablation rate of the pulsed laser on the intact optical component models made of different materials; S44: Calculate the percentage of the laser damage threshold of the intact optical component model of different materials and the laser damage threshold of the optical component model of the corresponding material after impact, and select the film layer and mirror material of the optical component based on the laser ablation rate of the pulsed laser on the intact optical component model and the optical component model after impact.

2. The laser damage threshold analysis method according to claim 1, characterized in that: The physical properties of the impactor include shape, density, size, impact velocity and impact angle; the physical properties of the target include density, specific heat capacity, melting point, maximum principal stress, shear modulus, Poisson's ratio, static yield limit and strain hardening modulus.

3. The laser damage threshold analysis method according to claim 1, wherein: In step S1, the impactor includes micrometeoroids and space debris, and the density of the micrometeoroids is in the range of 0.16 g / -4g / Between, the size range is 0.5 -1cm, the density of the space debris is 2.7 ; The density of the micrometeoroids is in the range of 0.16 g / to 4g / The density-mass relationship of the micrometeoroid is: ； Where m represents the mass of the micrometeoroid in g. is the density.

4. The laser damage threshold analysis method according to claim 1, wherein: The target body comprises a mirror surface and an optical film coated on the surface of the mirror surface, and the thickness of the mirror surface is at least five times the length of the impact object.

5. The laser damage threshold analysis method according to claim 1, wherein: In step S2, the LS-prepost built-in algorithm is used to extract the three-dimensional morphology data of the impact crater to obtain the crater depth and defect diameter of the target body; The calculation formula of the pit depth of the target body is: ； in, Because the pit is deep, is the impactor diameter, is the impactor density, is the impactor velocity, is the target density, is the target yield strength, is the modulus of the target; The defect diameter of the target is: ； in, is the defect diameter.

6. The laser damage threshold analysis method according to claim 1, characterized in that: In step S3, the structure of the optical element model is consistent with that of the target model in step S1.

7. The laser damage threshold analysis method according to claim 1, characterized in that: The complete optical element model is the optical element model that is not fitted with the three-dimensional morphology data in step S3.

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