Study On The Influence Of Surface Defects Of Optical Materials On Its Resistance To Laser Damage

High-power laser devices have been widely used in China’s national defense construction and related fields.A large number of optical components are required to transmit and control the laser beam,and fused silica and K9 glass are widely used due to their excellent optical properties.However,surface defects may occur during processing,transportation,and assembly,which may lead to laser-induced damage of the components,affecting the performance of the optical components and reducing the system’s load capacity.Thus,it is important to investigate the influence of surface defects of optical materials on their resistance to laser damage.In this paper,fused silica and K9 glass are taken as the research objects,through simulation modeling and experimental verification,to explore the influence of surface scratch defects and metal copper pollutants on their ability to resist laser damage.This paper first summarizes the generation and types of surface defects in optical materials,analyzes and compares the thermal damage mechanism and optical field damage mechanism of optical materials under intense laser irradiation.A theoretical model of optical materials under laser irradiation is established using the finite-difference time-domain method,providing a theoretical basis for establishing the relationship between surface defects in optical materials and their resistance to laser damage.Aiming at the theoretical simulation of surface defect-induced damage of optical materials,this paper establishes a three-dimensional finite-difference time-domain simulation model of scratch defects and contamination defects based on the surface characteristics of the two materials,and analyzes and calculates different structural parameters under 1064nm laser irradiation.effect on material damage.The light intensity enhancement factor(LIEF)represents the degree of field enhancement inside the material.The larger the field enhancement factor is,the more serious and concentrated the field enhancement inside the material is,and the material is more likely to be damaged,and vice versa.The simulation results show that the impact of scratch defects on fused silica and K9 glass is basically similar.The reflection and diffraction of the incident laser on the edge of the scratch cause the electric field inside the material and the rear surface to increase.The scratches within the incident wavelength range The light intensity enhancement factor reaches the maximum,and damage is prone to occur;the wider the scratch,the more obvious the inhibition effect on the field enhancement.Metal pollutants have strong absorption,and the strong diffraction effect will cause the electric field near the surface of the material to increase.The LIEF can reach up to 100,which can easily cause damage to the front surface of the substrate material.The size and location of defects generated during the processing and transportation of optical material components are very random,and it is difficult to carry out systematic and quantitative research on defect damage characteristics.In order to evaluate the influence of surface defects on the ability of materials to resist laser damage,this paper artificially uses nano-indentation Instrument and magnetron sputtering machine to create scratch defects and contamination defects on fused silica and K9 glass,observe the structural parameters of defects under white light interferometer,and then conduct laser damage test.The experimental results show that the rear surfaces of fused silica and K9 glass are extremely prone to damage.Under the action of 1064nm laser,the anti-laser damage thresholds of fused silica and K9 glass samples are 15.8J/cm~2 and20.5J/cm~2 respectively.At about the laser wavelength,the laser damage resistance thresholds of fused silica and K9 glass decreased by 33%and 32%,respectively.As the scratch depth continued to increase,the laser damage resistance thresholds first decreased and then stabilized.Due to the high absorption intensity of metal copper pollutants on light,it is easy to cause damage to the front surface of the material.When the size is 1mm,the damage threshold of the substrate has a significant impact.The damage threshold of the polluted fused silica and K9 glass substrates are both 10.0J/cm~2 and 15.4J/cm~2,respectively,so the substrate damage threshold increases negatively exponentially with the increase of the height of the pollutant,while the influence of the radius of the pollutant on the threshold is relatively small.