A method for evaluating laser damage threshold of optical materials based on multi-scale calculation of damage precursors

Abstract

The present invention discloses a method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors. (1) The present invention takes into account the Mie scattering theory, uses various types of damage precursors as laser absorption sources, and combines the heat transfer model to dynamically introduce laser energy into the optical material to evaluate the impact of the damage precursor on the material damage threshold. This is different from the existing simulation method of a simple surface fixed heat source (setting a local initial high temperature). (2) The present invention covers a variety of parameters related to optical materials. By adjusting the relevant parameters, the damage threshold and damage radius of various optical materials can be simulated and analyzed. This is different from the existing laser damage simulation model that only targets a single material.

Description

Technical field:

[0001] The present invention relates to the field of calculation and evaluation of damage precursors to laser damage thresholds of optical materials, and in particular to an evaluation method of damage precursors to laser damage thresholds of optical materials based on multi-scale calculation. Background technology:

[0002] The existing three-dimensional heat absorption model based on the general heat conduction equation can simulate the heat transfer process of optical materials under specific circumstances, analyze the temperature field distribution, and obtain damage-related information. However, these models can only analyze a certain optical material, and ignore the absorption process of laser energy by defects as damage precursors. They simply set high temperature as a heat source in a certain area of ​​the material to simulate the energy generated by laser-induced absorption. Summary of the invention:

[0003] The purpose of the present invention is to solve the existing problems and to provide a method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors.

[0004] The technical solution of the present invention is as follows: A method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors, comprising the following steps:

[0005] S1. Design the optical and thermodynamic properties of damage precursors and optical components: First, construct and optimize the optical material defect model in the presence of stable damage precursors. Secondly, obtain the structural density, electronic structure (band gap Eg) and dielectric function ε of the defect model in the presence of various damage precursors through first-principles calculations. Finally, use molecular dynamics calculations to obtain the various thermodynamic parameters of defect-free optical components at different temperatures, mainly including thermal conductivity k(T) and specific heat capacity Cp(T).

[0006] S2. Design the dynamic introduction of incident laser: first set the laser power density I and laser pulse width λ, and select the dielectric function ε of the precursor at this wavelength; then combine the size r, absorption cross section, scattering cross section and reflection cross section of the damaged precursor defect structure obtained by Mie scattering theory to complete the operation of embedding the heat source, and finally solve the laser energy Q absorbed by the damaged precursor defect as the heat source;

[0007] S3. Construct a macroscopic laser damage model combined with microscopic calculations for different optical materials: (1) Introduce the laser energy term Q into the conventional heat conduction model, and set boundary conditions in the contact area between the damage precursor and the optical element to improve the transmission process of laser energy from the precursor to the element; (2) Bring the temperature-related element parameters k(T) and Cp(T) into the model, and introduce the dynamic process of element performance changing with temperature; (3) Make the improved heat transfer model three-dimensional, add boundary conditions, and use the time domain difference method to solve and obtain the material lattice temperature distribution information during laser irradiation. Based on the above information and according to the criterion of thermal damage, calculate the damage threshold and damage radius of the optical material.

[0008] Preferably, the boundary conditions include but are not limited to setting the heat flow transfer state between the component surface and the air when solving the component surface damage problem.

[0009] Preferably, the criterion for determining the thermal damage is based on the critical temperature of the material lattice.

[0010] Preferably, the construction of the optical material defect model in S1 comprises the following steps: constructing the material crystal structure using MS software, establishing doping models of different defect types, and relaxing the structure using the DFT method.

[0011] Preferably, the various parameters of the damage precursor in S1 are used in the introduction process of the incident laser, and the various parameters of the optical element can be brought into the macroscopic laser damage model to simulate the dynamic laser damage process.

[0012] The beneficial effects of the present invention are:

[0013] (1) The present invention considers Mie scattering theory, uses various types of damage precursors as laser absorption sources, and combines the heat transfer model to dynamically introduce laser energy into the optical material to evaluate the impact of damage precursors on the material damage threshold. This is different from the existing simulation method of simply fixing the surface heat source (setting the local initial high temperature).

[0014] (2) The present invention covers a variety of parameters related to optical materials. By adjusting the relevant parameters, the damage threshold and damage radius of various optical materials can be simulated and analyzed. This is different from the existing laser damage simulation model that only targets a single material.

[0015] (3) The present invention combines the microscopic properties of defects (light absorption, band gap, etc.) with the macroscopic properties of optical materials (thermodynamic properties), which is different from existing theoretical models that focus on the macroscopic or microscopic scale.

[0016] (4) The present invention can control the incident laser parameters, thereby analyzing the influence of laser parameters (pulse width, power density, etc.) on the damage threshold of optical materials. This is different from the theoretical model of laser damage for a single wavelength. Description of the drawings:

[0017] Figure 1 It is a schematic diagram of the process of the present invention;

[0018] Figure 2 The temperature field distribution of fused quartz in Example 1 when the damage threshold is reached under laser irradiation with a power density of 1.7 GW / cm2, a pulse width of 5 ns, and a wavelength of 355 nm;

[0019] Figure 3 The temperature field distribution of fused quartz when the damage threshold is reached under different laser pulse widths in Example 1;

[0020] Figure 4 The temperature field distribution on the surface of single crystal silicon in Example 2 when the ambient temperature is 300K, the pulse width is 400ps, and the laser energy is 0.36j / cm2;

[0021] Figure 5 This is a graph showing the relationship between the laser-induced damage threshold of single-crystal silicon material and the ambient temperature, with iron as the damage precursor in Example 2; Specific implementation method:

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0024] The method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors includes the following steps:

[0025] S1. Design the optical and thermodynamic properties of damage precursors and optical components: First, construct and optimize the optical material defect model in the presence of stable damage precursors. Secondly, obtain the structural density, electronic structure (band gap Eg) and dielectric function ε of the defect model in the presence of various damage precursors through first-principles calculations. Finally, use molecular dynamics calculations to obtain the various thermodynamic parameters of defect-free optical components at different temperatures, mainly including thermal conductivity k(T) and specific heat capacity Cp(T).

[0026] S2. Design the dynamic introduction of incident laser: first set the laser power density I and laser pulse width λ, and select the dielectric function ε of the precursor at this wavelength; then combine the size r, absorption cross section, scattering cross section and reflection cross section of the damaged precursor defect structure obtained by Mie scattering theory to complete the operation of embedding the heat source, and finally solve the laser energy Q absorbed by the damaged precursor defect as the heat source;

[0027] S3. Construct a macroscopic laser damage model combined with microscopic calculations for different optical materials: (1) Introduce the laser energy term Q into the conventional heat conduction model, and set boundary conditions in the contact area between the damage precursor and the optical element to improve the transmission process of laser energy from the precursor to the element; (2) Bring the temperature-related element parameters k(T) and Cp(T) into the model, and introduce the dynamic process of element performance changing with temperature; (3) Make the improved heat transfer model three-dimensional, add boundary conditions, and use the time domain difference method to solve and obtain the material lattice temperature distribution information during laser irradiation. Based on the above information and according to the criterion of thermal damage, calculate the damage threshold and damage radius of the optical material.

[0028] Specifically, the boundary conditions include but are not limited to setting the heat flow transfer state between the component surface and the air when solving the component surface damage problem.

[0029] Specifically, the criterion for the thermal damage is based on the critical temperature of the material lattice.

[0030] Specifically, the construction of the optical material defect model in S1 includes the following steps: constructing the material crystal structure using MS software, establishing doping models of different defect types, and relaxing the structure using the DFT method.

[0031] Specifically, the various parameters of the damage precursor in S1 are used in the introduction process of the incident laser, and the various parameters of the optical element can be brought into the macroscopic laser damage model to simulate the dynamic laser damage process.

[0032] Example 1

[0033] The damage threshold of fused quartz material under triple frequency laser irradiation under different laser pulse widths was simulated when neutral oxygen vacancy defects were used as damage precursors. Firstly, a fused quartz defect model with a large number of neutral oxygen vacancy defects was constructed, and the complex refractive index was 1.08-0.16i and Eg was 6.08eV calculated by first-principles. Then, the molecular dynamics method was used to simulate and calculate the k(T) and Cp(T) of defect-free fused quartz. The defect size was set to 200nm and the density of fused quartz was 2.2g / cm3. All parameters were brought into the thermal transfer model with added boundary conditions. By adjusting the laser power density I (GW / cm2) and the laser pulse width λ (ns), the damage threshold of fused quartz material under triple frequency laser irradiation under different laser pulse widths was finally obtained. Figure 2 The temperature field distribution of the fused quartz surface at different times under laser irradiation with a power density of 1.7GW / cm2, a pulse width of 5ns, and a wavelength of 355nm. In the figure, the black and red curves represent that when the laser is acting, the absorption wavefront advances with the temperature, generating a black curve every 0.5ns; and a red curve every 0.25. The results show that when the laser power density is 1.7GW / cm2, the central temperature of the precursor increases greatly, directly rising to about 14500K. At this time, the radius of the obvious high-temperature area on the fused quartz surface will reach 650nm. In addition, when the irradiation time exceeds 4ns, that is, the red curve part, the temperature of the precursor area rises rapidly, and the propagation range of the high temperature also increases greatly, and an obvious absorption wavefront appears. Figure 3 The temperature field distribution on the surface and inside of fused quartz when the damage threshold is reached under different laser pulse widths is shown. The smaller the pulse width, the smaller the damage threshold. This simulation result satisfies the square root relationship found in the experiment (the damage threshold is proportional to the square root value of the pulse width).

[0034] Example 2

[0035] Taking iron as the damage precursor, the damage threshold of single crystal silicon material under 1064nm laser irradiation at different ambient temperatures is simulated. First, the dielectric function of the precursor defect model and k(T) and Cp(T) of single crystal silicon are obtained by first-principles calculation and molecular dynamics calculation. Then the laser parameters are set to a wavelength of 1064nm and a pulse width of 400ps. By manually setting the surface temperature of single crystal silicon, the damage threshold of single crystal silicon material under 1064nm laser irradiation at different ambient temperatures is simulated. Figure 4 The display shows the temperature distribution of the single crystal silicon surface under room temperature and laser energy of 0.36j / cm2. At this time, the temperature of the central area reaches 4000K, which can be judged as exceeding the damage threshold (the damage threshold is based on the surface temperature exceeding 1500K, and 1500K is the melting point of single crystal silicon material). The damage threshold results at different ambient temperatures are shown in Figure 2. Figure 5As shown, it can be seen that there is a linear relationship between ambient temperature and damage threshold. As the ambient temperature gradually increases, the damage threshold of single crystal silicon material decreases accordingly.

[0036] The above description is only used to understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the rights of the present invention.

Claims

1. A method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors, characterized in that: The following steps are involved: S1. Design the optical and thermodynamic properties of the damage precursor and optical element: First, construct and optimize the optical material defect model in the presence of a stable damage precursor. Second, obtain the structural density, electronic structure band gap Eg and dielectric function ε of the defect model in the presence of various damage precursors through first-principles calculations. Finally, use molecular dynamics calculations to obtain the thermodynamic parameters of defect-free optical elements at different temperatures, mainly including thermal conductivity k(T) and specific heat capacity Cp(T). S2. Design the dynamic introduction of incident laser: first set the laser power density I and laser pulse width λ, and select the dielectric function ε of the precursor at this wavelength; then combine the size r, absorption cross section, scattering cross section and reflection cross section of the damaged precursor defect structure obtained by Mie scattering theory to complete the operation of embedding the heat source, and finally solve the laser energy Q absorbed by the damaged precursor defect as the heat source; S3. Construct a macroscopic laser damage model combined with microscopic calculation for different optical materials: (1) Introduce the laser energy term Q into the conventional heat conduction model, and set the boundary conditions in the contact area between the damage precursor and the optical element to improve the transmission process of laser energy from the precursor to the element; (2) Bring the temperature-related element parameters k(T) and Cp(T) into the model, and introduce the dynamic process of element performance changing with temperature; (3) Make the improved heat transfer model three-dimensional, add boundary conditions, and use the time domain difference method to solve and obtain the material lattice temperature distribution information during laser irradiation. Based on the above information and according to the criterion of thermal damage, calculate the damage threshold and damage radius of the optical material; The surface and internal temperature field distribution of fused quartz when the damage threshold is reached under different laser pulse widths shows that the smaller the pulse width, the smaller the damage threshold.

2. The method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors according to claim 1, characterized in that: The boundary conditions include but are not limited to setting the heat flow transfer state between the component surface and the air when solving the component surface damage problem.

3. The method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors according to claim 1, characterized in that: The criterion for the thermal damage is based on the critical temperature of the material lattice.

4. The method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors according to claim 1, characterized in that: The construction of the optical material defect model in S1 includes the following steps: constructing the material crystal structure using MS software, establishing doping models of different defect types, and relaxing the structure using the DFT method.

5. The method for evaluating the laser damage threshold of optical materials based on multi-scale calculation of damage precursors according to claim 1, characterized in that: The various parameters of the damage precursor in S1 are used in the introduction process of the incident laser, and the various parameters of the optical element can be brought into the macroscopic laser damage model to simulate the dynamic laser damage process.

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