A brittle material optical element laser damage evaluation method considering stress concentration
By establishing a laser damage assessment method for brittle material optical elements that takes stress concentration into account, the error problem of traditional assessment methods has been solved, achieving high-precision laser damage assessment and improving the strike accuracy of laser weapons and the lightweighting of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTH WEST INST OF TECHN PHYSICS
- Filing Date
- 2022-12-29
- Publication Date
- 2026-07-24
AI Technical Summary
Existing technologies are insufficient to accurately assess the laser damage state of optical components made of brittle materials. Traditional methods have significant errors and do not consider the impact of internal stress concentration on failure.
By calculating the maximum local stress inside the component and combining optical and thermodynamic theories, a simulation model is established to evaluate the failure state of the optical component and consider the impact of stress concentration on brittle materials.
It has achieved high-confidence laser damage assessment, improved the accuracy of laser weapon systems in striking different targets, and promoted the lightweighting and miniaturization of laser weapon systems.
Smart Images
Figure CN116183167B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of laser damage technology and relates to a laser damage assessment method for brittle material optical components that takes stress concentration into account. Background Technology
[0002] With the continuous development of weaponry research and development technology, laser weapons, as one of the new concept weapons, have gradually become a key focus of weaponry development in countries around the world. Countries worldwide regard laser weapons as an important means to enhance their deterrence and strike capabilities. Laser weapons are directed-energy weapons that use high-energy laser beams to directly destroy targets. They are characterized by high attack speed, accurate positioning, no recoil, and low cost. With the development of new long-range precision unmanned equipment, laser weapons are being widely deployed in modern warfare. However, due to the extremely high output energy requirements of laser weapons, their current size and weight are very large, posing a significant obstacle to the future development of lightweight and miniaturized weaponry.
[0003] To optimize the performance parameters of laser weapons, accurate and effective assessment of their destructive power is crucial. Current theoretical evaluation methods, such as thermal diffusion and thermal ablation, can analyze the damage characteristics of typical targets like metals and plastics under intense laser irradiation. However, the window elements of precision-guided weapon optics typically utilize high-strength, impact-resistant optical materials. Traditional theoretical calculation methods suffer from significant errors in assessing laser damage to these typically brittle materials. This is primarily because the internal mechanical properties of brittle materials often play a more significant role in component failure than thermal damage. Furthermore, these optical elements are generally manufactured using ultra-precision grinding and polishing processes. While the surface roughness of the finished product can reach sub-nanometer levels, structural defects inevitably remain on the surface or subsurface. These defects further exacerbate internal stress concentration, increasing the risk of material fracture. Currently, a high-confidence laser damage assessment for brittle material optical elements remains an unresolved issue in the field of laser damage assessment for components. Summary of the Invention
[0004] (I) Purpose of the Invention
[0005] The purpose of this invention is to propose a laser damage assessment method for brittle material optical components that takes stress concentration into account. By calculating the maximum local stress inside the component and based on the fracture criteria of brittle materials, the failure state of the optical component can be assessed more accurately.
[0006] (II) Technical Solution
[0007] To address the aforementioned technical problems, this invention provides a laser damage assessment method for brittle material optical components considering stress concentration, comprising the following steps:
[0008] Step 1. Determine the type of target material for high-intensity laser irradiation. For brittle optical materials, obtain their fracture strength parameters through theoretical or experimental methods.
[0009] Step 2. Use a microscope to inspect the morphology and size of surface or subsurface defects of the optical element to obtain the lateral dimension w and longitudinal dimension d of the defects;
[0010] Step 3. Obtain the target laser power density through relevant theories or experimental methods such as laser atmospheric transmission, and determine the laser wavelength and irradiation time. If it is a pulsed laser, the pulse width and frequency also need to be determined.
[0011] Step 4. Based on optical and thermodynamic theories, establish a simulation model of stress concentration inside optical materials induced by defect structures, and compare and analyze the stress magnitude caused by defect structures of different shapes and sizes in the laser-acting region;
[0012] Step 5. Select the value of the maximum internal stress of the brittle optical material and compare it with the material fracture strength parameter. According to the fracture criterion of brittle materials, evaluate the damage and failure state of the component under the laser parameter irradiation.
[0013] Furthermore, the specific process of step 4 is as follows:
[0014] 4.1 Solving for the energy density distribution near optical element defects:
[0015] Since component defects are generally much smaller than the laser spot size, the laser in the defect region is simplified as a uniform time-harmonic plane electromagnetic wave as the incident excitation. The propagation equation of the excited electromagnetic wave inside the component is:
[0016]
[0017] In the formula, E represents the electric field intensity vector, k is the wave vector, and ε r is the relative permittivity of the optical element.
[0018] When a powerful laser beam propagates inside an optical element, the energy concentration of the light intensity I is related to the square of the electric field modulus |E|. 2 It is directly proportional to the power density of the laser applied to the target, so the energy density distribution near the defect of the optical element can be obtained from the power density of the laser applied to the target.
[0019] 4.2 Solving for the temperature distribution near defects in optical components:
[0020] Using the light intensity energy density distribution near the defect as input, and combining the thermal absorption characteristics of optical materials, solve the heat conduction equation:
[0021]
[0022] Where ρ is the material density, T is the temperature, and k is the kJ / m³ / s. Tα is the thermal conductivity coefficient, and α(T) is the thermal absorption coefficient that varies with temperature.
[0023] Solving the above equations will yield the temperature distribution near the defects in the optical element.
[0024] 4.3 Solving for stress distribution near defects in optical components:
[0025] Non-uniform temperature distribution within the optical element can cause local expansion, triggering transient displacement fields. For thermoelastic materials, Navier functions can be used to describe this. The stress distribution near defects in the optical element can be solved using the material constitutive equations.
[0026] Based on the stress concentration phenomenon caused by defects in the structure of optical components, the magnitude of local stress caused by defects of different shapes and sizes in the laser-acted area is compared and analyzed.
[0027] (III) Beneficial Effects
[0028] The laser damage assessment method for brittle material optical elements considering stress concentration provided by the above technical solution not only enables high-confidence laser damage assessment of brittle material optical elements, but also lays the foundation for establishing a database of laser-damaged target characteristics and damage effects based on statistical results of the morphology and size characteristics of initial defect points on the surface or subsurface of optical elements. Ultimately, this improves the accuracy of laser weapon system simulation analysis in striking different targets. Furthermore, based on optical and thermodynamic theories, this invention conducts comparative simulation analysis of the stress concentration effects caused by defect structures in different brittle material optical elements, enabling the optimization of parameters such as laser wavelength and pulse width. This helps in planning the optimal laser emission power, significantly improving the strike efficiency of laser weapons. This method not only facilitates the establishment of a future high-confidence laser damage database, but also provides a theoretical basis and parameter guidance for optimizing performance indicators such as lightweighting and miniaturization of laser weapon systems. Attached Figure Description
[0029] Figure 1 A schematic diagram of a simulation model for stress concentration inside optical materials induced by defect structures.
[0030] Figure 2 This is a schematic diagram of the simulation results of the internal energy distribution of optical materials induced by defect structures.
[0031] Figure 3 This is a schematic diagram of the simulation results of the internal temperature distribution of optical materials induced by defect structures.
[0032] Figure 4 This is a schematic diagram of the simulation results of stress concentration inside optical materials induced by defect structures. Detailed Implementation
[0033] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.
[0034] This embodiment considers the laser damage assessment method for brittle material optical components under stress concentration, which includes the following steps:
[0035] Step 1. The target material of the high-intensity laser irradiation target is determined to be fused silica, a typical brittle optical material. Its fracture strength is determined to be 20-60 MPa through indentation finite element simulation and material fracture experiments.
[0036] Step 2. The high-resolution ultra-depth-of-field microscope used is the VH-1000E ultra-depth-of-field stereomicroscope system manufactured by Keyence Corporation of Japan. It can be used for the precise detection of the lateral and longitudinal depth dimensions of surface or subsurface defects of optical components. The maximum magnification can reach 5000x, and the depth direction detection can achieve a resolution of 1μm. It can detect the morphology and size of surface or subsurface defects and obtain the lateral dimension w (width) and longitudinal dimension d (depth) of the defects.
[0037] Step 3. The measured laser power density at the target was determined to be 71 W / cm². 2 The continuous laser wavelength is 1064nm, and the irradiation time is 5s.
[0038] Step 4. Based on optical and thermodynamic theories, establish a simulation model of stress concentration within optical materials induced by defect structures, such as... Figure 1 As shown.
[0039] Step 4.1. Solving for the energy density distribution near the optical element defect:
[0040] Since component defects are generally much smaller than the laser spot size, the laser in the defect region is simplified as a uniform time-harmonic plane electromagnetic wave as the incident excitation. The propagation equation of the excited electromagnetic wave inside the component is:
[0041]
[0042] In the formula, E represents the electric field intensity vector, k is the wave vector, and ε r is the relative permittivity of the optical element.
[0043] When a powerful laser beam propagates inside an optical element, the energy concentration of the light intensity I is related to the square of the electric field modulus |E|. 2 Proportional to the target laser power density, the energy density distribution near the optical element defect can be obtained from the target laser power density. For a surface defect with a transverse dimension w of 1 μm and a longitudinal dimension d of 3 μm, the nearby light intensity energy distribution is as follows: Figure 2 As shown.
[0044] 4.2 Solving for the temperature distribution near defects in optical components:
[0045] Using the light intensity energy density distribution near the surface defects of the fused silica element as input, and combining the thermal absorption characteristics of optical materials, the heat conduction equation is solved:
[0046]
[0047] Where ρ is the material density, T is the temperature, and k is the kJ / m³ / s. T α is the thermal conductivity coefficient, and α(T) is the thermal absorption coefficient that varies with temperature.
[0048] Solving the above equations yields the temperature distribution inside the material induced by the defect structure of the fused silica optical element, such as... Figure 3 As shown.
[0049] 4.3 Solving for stress distribution near defects in optical components:
[0050] The non-uniform temperature distribution inside the fused silica element causes local expansion, exciting transient displacement fields. For thermoelastic materials, Navier functions can be used to describe this. The stress distribution near defects in the optical element is then solved using the material constitutive equations.
[0051] Based on the stress concentration phenomenon caused by defects in the optical component structure, this paper compares and analyzes the magnitude of local stress caused by defects in the laser-acted region, such as... Figure 4 As shown.
[0052] Step 5. Compare the maximum internal stress value of the brittle optical material with the material fracture strength parameter. It is found that under this condition, the stress value at the crack tip of the fused silica is much greater than its tensile fracture strength. According to the fracture criterion of brittle materials, it is judged that the element will be in a fracture failure state under the irradiation of this laser parameter.
[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for evaluating laser damage to brittle material optical components considering stress concentration, characterized in that, Includes the following steps: Step 1. Determine the type of target material for high-intensity laser irradiation. For brittle optical materials, obtain their fracture strength parameters. Step 2. Use a microscope to inspect the morphology and size of surface or subsurface defects of the optical element to obtain the lateral dimension w and longitudinal dimension d of the defects; Step 3. Determine the target laser power density, laser wavelength, and irradiation time. For pulsed lasers, determine the pulse width and frequency. Step 4. Based on optical and thermodynamic theories, establish a simulation model of stress concentration inside optical materials induced by defect structures, and compare and analyze the stress magnitude caused by defect structures of different shapes and sizes in the laser-acting region; Step 5. Select the value of the maximum internal stress of the brittle optical material and compare it with the material fracture strength parameter. According to the fracture criterion of brittle materials, evaluate the damage and failure state of the component under the laser power density, laser wavelength, irradiation time, pulse width and frequency irradiation. In step 1, the fracture strength parameter of the brittle optical material is obtained through theory or experiment; In step 3, the target laser power density is obtained through laser atmospheric transmission theory or experiments; Step 4 includes the following sub-steps: 4.1 Solving for the energy density distribution around defects in optical components; 4.2 Solving for the temperature distribution around defects in optical components; 4.3 Solving for stress distribution around defects in optical components; In step 4.1, since the component defect is much smaller than the laser spot size, the laser in the defect region is simplified as a uniform time-harmonic plane electromagnetic wave as the incident excitation. The propagation equation of the excited electromagnetic wave inside the component is: In the formula, E represents the electric field intensity vector, k is the wave vector, and ε r The relative permittivity of the optical element; When a powerful laser beam propagates inside an optical element, the energy concentration of the light intensity I is related to the square of the electric field modulus |E|. 2 Proportional to the target laser power density, the energy density distribution around the optical element defect is obtained; In step 4.2, using the light intensity energy density distribution around the defect as input, and combining the thermal absorption characteristics of the optical material, the heat conduction equation is solved: in, ρ is the material density, T is the temperature, and kJ / m³ is the kJ / m³ temperature. T α is the thermal conductivity coefficient, and α(T) is the thermal absorption coefficient that varies with temperature; Solving the above equations yields the temperature distribution near the defects in the optical element. In step 4.3, the non-uniform temperature distribution inside the element causes local expansion of the element, which excites a transient displacement field. For thermoelastic materials, the Navier function is used to describe it. According to the material constitutive equation, the stress distribution near the defects of the optical element is solved.