A Research Of Metal Impurity Induced Laser Damage On Fused Silica Element And Dynamic Repair

The damage resistance of a large-scale high-power laser device is a core technical capacity that uses the principle of inertial confinement fusion to solve the energy crisis for humanity in the future.The damage threshold value of the fused silica element directly restricts the future increase of the laser energy density of the ignition device.Metal impurities are one of the main reasons for reducing the damage threshold of fused silica components.The changes of temperature and stress fields are recognized by analyzing and simulating the physical processes of metal impurities induced fused silica damage and repair damage.In order to prolong the service life of fused silica components as much as possible and ensure the stable operation of large-scale high-power laser devices,it is necessary to increase the damage threshold of fused silica components according to the characteristics of radiation damage,and it is important to use damage repair technology to suppress the increase in the damage of fused silica components.Using the finite element analysis software COMSOL for simulation,the physical process of metal impurity induced fused silica element irradiation damage and repair damage has been numerically simulated.The research and conclusions of this paper are as follows:(1)By analyzing the distribution of temperature field induced by metal impurities in the fused silica element,the irradiation damage is analyzed.The width of the fused silica element is 20 mm and the thickness is 10 mm.The long axis of the ellipsoidal metal impurity is 30μm and the short axis is 10μm.The metal impurity is using Cu in the material library and the temperature of the metal impurities changes very much after the high-power laser irradiation(laser power is 250 W and spot radius is 2.5mm).At 0.05 s,the metal impurity temperature had reached 2000 K.At 0.45 s,the temperature of the metal impurity had reached as high as 4000 K,far exceeding the melting point of fused silica,and the surface configuration of the fused silica element began to be destroyed.(2)By analyzing the stress field distribution induced by metal impurities in the fused silica element,it is found that the maximum value of the melt flow rate appeared in the radial direction of 600μm from the center of the spot,and the maximum flow velocity is 9.88×10-4m/s.The maximum value of the stress pressure is at the maximum of the melting velocity and the maximum pressure is 748 Pa.Finally,it was found that the damage characteristics of spherical and ellipsoid metal impurities induced are very similar,while the damage pits caused by thin film metal impurities are the smallest.(3)By analyzing the temperature field distribution of CO2 laser-irradiated fused silica element damage repair,the CO2 laser power is 50 W and the spot size is 0.02 mm.The damage pit depth is 0.4μm and the width is 3μm.At 0.5s,the temperature at the center light spot had reached 2300 K,exceeding the melting point of fused silica.At 4.5s,the irregular damage pit structure of the fused silica element had been repaired to a smooth Gaussian structure.(4)By analyzing the stress field distribution of CO2 laser-irradiated fused silica element damage,it is found that the maximum value of the melt flow velocity appeared in the radial direction of 6μm from the center of the spot,and the maximum flow velocity is 2.07×10-6m/s.The maximum value of the stress pressure is at the maximum of the melting velocity and the maximum pressure is 4320 Pa.Finally,it is concluded that the irradiation time and the laser power are very similar,and the radius of the light spot has the most obvious effect on the depth of the damage pit repair.