| How to improve the LIDT(Laser Induced Damage Threshold)of optical components is the crucial problem of developing ICF(Inertial Confinement Fusion)technology.Al2O3 is a material widely used in high-power laser amplifiers,and the main factor causing the reduction of its laser-induced damage resistance is the residual microstructure and surface pollutants on its processed surface.Laser damage will occur under the irradiation of high energy stray light gathering point(ghost reflection),which restricts the development of ICF Technology.Therefore,it is of great significance to study the influence of micro nano structure and pollutants on the laser damage resistance of Al2O3.In this dissertation,the effects of surface micro nano structure and solid particles on the laser damage resistance of Al2O3 surface are systematically analyzed,and the distribution of temperature and stress under laser irradiation is discussed.The adsorption and desorption behavior of organic pollutants on the surface of Al2O3 with different morphologies is studied in order to reduce the laser damage caused by organic pollution.The simulation of laser micro nano structure is verified by experimental method,and the damage of different surface topographies under laser irradiation is observed.The main work is as follows:1.The types of machined surface defects are analyzed,and some typical micro nano structure types of Al2O3 surface are extracted.A computational model for the interaction between laser and Al2O3 is established.Then the ideal plane,rectangular groove structure and saw tooth groove structure under pulsed laser irradiation are simulated,respectively.The laser damage is analyzed from the perspective of the distribution of temperature and stress in the microstructure region and substrate.2.The sources and classification of pollutants in high-power laser amplifiers are analyzed.A finite element simulation model(FEM)is established to study the damage caused by typical solid particle contaminants(Al,Fe,Cu,Cr and Ce O2)on the surface of Al2O3 under laser irradiation.The effects of impurity types,impurity radius and impurity depth on the LIDT of Al2O3 substrate are studied from the point of temperature and stress distribution.It is found that there is a critical size value which maximizes the damage.3.The C12 in the high power amplification system is selected as a typical organic contaminant to study the laser damage induced by organic pollutants on the surface of Al2O3,Molecular dynamics method(MD)is adopted to simulate the adsorption and desorption process,The the adsorption and dedsorption mechanisms and laws for different surface structures are studied.The effects of surface organic pollutants on laser induced damage are also analyzed.4.A laser target experiment was carried out to study the damage of Al2O3 under different surface topographies.The sawtooth grooves were set up.After that,the morphology changes before and after shooting were observed.Subsequently,the simulation of laser action was verified.Moreover,this paper performed the target experiment of surfaces before and after polishing with different roughness.The damage law was revealed according to the n?mber of damaged particles,and the effect of surface morphology on the laser damage resistance of Al2O3 was analyzed.In this dissertation,the FEM is used to analyze the laser damage resistance of Al2O3 from the perspective of micro nano structure and solid pollutants.The mechanism of adsorption and desorption of organic pollutants is analyzed by MD method,which can be used for reference for the removal of pollutants and the improvement of the laser induced damage resistance. |
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