First-principles Calculation Of Laser Irradiation Effect Of Fused Silica With Impurities

Fused Silica,as the most common optical element in high-power laser systems,is widely used in large-scale laser devices for inertial confinement fusion.However,high-frequency laser irradiation can cause various laser-induced damages such as densification,cracks,jetting,melting,and pits in fused silica materials.The laser damage will seriously reduce the light transmission performance of the material,and greatly reduce the service life of optical components,which seriously restricts the research and development of con-trollable nuclear fusion.Therefore,it is very important to study and analyze the causes of light damage caused by fused silica laser irradiation and find ways to increase the laser damage resistance threshold of fused silica components.Laser-induced damage of fused silica components is mainly caused by mechanical fracture defects and impurity contamination defects.Experiments have proved that pol-ishing is an effective method to deal with mechanical fracture defects,but the polishing process will also cause metal impurities represented by iron to enter the fused silica.In recent years,researchers have found through experiments that pickling and etching can significantly reduce the impurity content on the surface and subsurface of fused silica.However,the removal of remaining impurities has become increasingly difficult.There-fore,it is becoming more and more important to study the influence of residual impurities on the damage threshold of fused silica laser.Iron impurities and aluminum impurities are two representative impurities that are widely present in fused silica amorphous materials.They are often unavoidable infiltra-tion in the production and processing of fused silica components,and are one of the im-portant reasons for the lowering of the laser damage threshold of fused silica.Therefore,studying the laser damage mechanism of fused silica containing such metal impurities is of great significance for improving the working life of fused silica laser transmission de-vices.This paper is based on density functional theory,using first-principles combined with plane wave pseudopotential methods to study the effects of iron(Fe)and aluminum(Al)impurities on the laser damage of the amorphous structure of fused silica.Specific work includes:1)Construction of pure fused silica structure model,iron-containing impurity fused silica structure model,and aluminum-containing impurity structure model.The bond fused silica model was constructed using the BSMC program based on the Monte Carlo algorithm,and the bond length and bond angle distribution of the model were counted to judge the rationality of the structure.On this basis,gap doping is used to construct struc-tural models of iron-containing impurity fused silica and aluminum-containing impurity fused silica.2)Analyze the microstructure and electronic properties of fused silica containing iron impurities and fused silica containing aluminum impurities.Statistic of bond length and bond angle distribution of fused silica after doping,compared with before doping.Calculate the electronic density of states of pure fused silica,iron-containing impurity fused silica,and aluminum-containing impurity fused silica,and analyze the change of state density before and after doping.3)Use the VASP software to calculate the molecular dynamics module from scratch to simulate the relaxation process of fused silica after absorbing photon energy by laser ir-radiation.Analyzed the microstructure and electronic structure changes of iron-containing impurity fused silica and aluminum-containing impurity fused silica models before and after simulated irradiation,and concluded that iron atoms cause fused silica to tend to be dense under laser irradiation.And it is found that the inclusion of these two impurities will have a significant impact on the laser irradiation effect of the fused silica model,es-pecially iron impurities can cause significant changes in the electronic energy level of the fused silica before and after the energy is absorbed(irradiation),such as the narrowing of the band gap,Absorption peak position shift,etc.