Study On Thermal Characteristics Of Laser Induced Damage In Optical Materials

The study of laser-induced damage in optical materials has always been one of the most important problems in high-power laser facility.The high-power-density laser pulse puts forward strict requirements for the laser damage resistance of the optical material.The material damage directly affects the safe operation of the laser system and limits its output capability.Therefore,it is of great significance to study how to improve the damage threshold of optical materials.Analytical methods and numerical calculation methods are used to theoretically analyze the interaction mechanism of laser and materials.The analytical method is computationally complex and applies to only a few cases;the finite element method(FEM)has great flexibility and a strong ability to handle complex problems compared with the finite difference method.Based on this,this paper applied software ANSYS based on FEM to calculate field effects of laser-pulse-induced damage in optical glass and optical film.The modulation of impurity defects on laser energy distribution was considered,and the physical laws of damage generation were analyzed which provided a reference value for improving the application of laser system in scientific research,national defense,production and other fields.In this thesis,the calculation of the optical material damage model irradiated by laser pulse based on ANSYS was mainly investigated,and the development law of laser damage was analyzed.The thermal diffusion pattern and stress action pattern of laser energy in the model were given based on Fourier heat conduction theory and classical thermoelastic theory,and then the thermal effects of laser-induced damage in optical materials were analyzed in detail with FEM.The theoretical models of laser damage in optical glass(k9 glass and fused silica)and impurity-induced damage in K9 glass ware established.The influence of laser parameters and material properties on damage threshold was analyzed.In addition,the transient temperature and stress field distribution of the film-substrate interface were calculated,and the field effect analysis of the optical film modulated by laser pulse was studied.Results show that the thermal stress damage in K9 glass is mainly determined by the hoop stress,and the bulk damage occurs earlier than surface damage below the melting temperature.The tensile stress damage threshold,compressive stress damage threshold and the melting damage threshold in K9 sample are 4.62,8.40 and 10.25 J/cm2,respectively,which means that the process of damage generation is 'stress before melt,stretch berore compress'.The maximum thermal stress in K9 glass is about 19 times that of fused silica at the same laser parameters.The film-substrate interface has high temperature and thermal stress,and the TiO2 film is damaged before the K9 substrate.The field-modulated HfO2 film of surface layer has the highest electric field strength when the optical film irradiated by laser pulse.The light field intensity modulated by Pt-impurity makes the film area near the impurity become weak position of laser damage,and the highest electric field strength and temperature increase approximately linearly as the impurity size increases.