Research On Thermal Effect Of Laser Irradiated Optical Materials Based On The Finite Element Method

With the development of laser technology,laser is applied more and more widely in life and it develops in the direction of higher power and higher energy after the emergence of high power laser based on solid-state technology.Thermal effect of optical components in laser systems such as the output coupler,a folding mirror and output window and so on become the main factors limiting the output beam quality of high-power laser system.In order to make better use of the laser,especially high power and high energetic laser and expand the application field of laser,the study on the thermal effect of laser irradiating optical materials has important practical value for improving the laser damage resistance of optical materials.The main reference point is that the finite element method is used to study the thermal effect of optical materials under intense laser irradiation.The mechanism of the interaction between the laser and the material is analyzed.Especially,the absorption mechanism of the laser beam and the damage mechanism of the material are studied under the intense laser irradiation and the finite element formulation for calculating the temperature field of threedimensional model of arbitrary material is deduced.The temperature field distribution of the real optical lens model is obtained and the mechanism and influence of the different defects of the material on the laser-induced damage are studied.The main work is as follows:1.The mechanism of interaction between laser and material is introduced in detail.The absorption and reflection of irradiated laser are studied from the macroscopic point of view.Electromagnetic theory is used to derive the formula.From the microscopic point of view,Thermal stress damage,avalanche ionization damage,multi-photon ionization damage and impurity defect destruction mechanism are analyzed and the differential expression of the heat transfer equation is derived according to the law of conservation of energy and Fourier experimental law.2.Based on the finite element method,a detailed formula derivation of the parabolic partial differential equation is given.The finite element calculation program of temperature field distribution of arbitrary three dimensional model material under laser irradiation is prepared by using MATLAB language.The results are consistent by using the software ABAQUS to verify the program kernel and verify the correctness of the programming.3.The finite element model of the optical element is established by using the optical lens,which is commonly used in the optical system.The influence of different laser parameters and material parameters on the temperature field distribution are analyzed.The anti-laser damage threshold of quartz glass and K9 glass material is obtained,which can provide reference for the selection of optical components in optical system and the ability of antilaser damage of optical components.4.The problem of laser-induced damage of material defects including cracks and impurities in the process of material processing is studied.By analyzing the temperature field and stress field of the laser irradiation under the condition of defects,it is found that these defects in the material will reduce the laser damage threshold of the material,especially the impurity.Impurities are the most serious absorption of laser energy,which is the main factor leading to laser induced damage.Under the condition that the laser parameters are constant and the laser is completely covered with impurities,the larger the impurity size,the more absorbed the laser energy,the more likely to lead to damage to the material.5.The thermal field effect of the laser irradiation on the multi-layer dielectric model of the CCD detector is simulated.By analyzing the temperature field distribution and the stress field distribution of the layers under the irradiation of the pulsed laser,it is found that with the increase of the laser power,the temperature and stress of the irradiation layer are increasing,and the change of the silicon layer is the most prominent.Therefore,it is concluded that the silicon layer easily leads to the damage of the CCD and the effect of temperature is greater than that of the stress.When the power of the irradiated laser is increased to a certain value,the multilayer dielectric model of the CCD will be stratified to melt,which leads to CCD damage or failure.