Research On Thermal Effects Of Optical Components Irradiated By High-power Continuous-wave Laser Beam

High-power lasers have become an important tool for cutting-edge scientific research and advanced technology research,and are widely used in particle acceleration,fusion energy,laser processing,military defense and other fields.Output capability and beam quality are two core properties pursued when developing high-power laser systems.For high average power laser systems,the thermal effects in optical components irradiated by continuous-wave(CW)laser are inextricably linked to the output performance of the laser system.In this paper,the thermal effects in optical components irradiated by high-power CW laser are studied.The contents are as follows:First,the theory of heat conducticity and thermoelasticity based on linear model and nonlinear model are studied.The analytical solution of the temperature of a radially infinite and finite sample irradiated by CW laser is deduced,and the solution process of typical two-dimensional,approximate three-dimensional and strict three-dimensional thermoelastic problems are combed.The nonlinear model of thermal effects of compnents irradiated by high-power CW laser is established,and the related theories of heat conductivity and thermoelasticity based on nonlinear model are introduced.Secondly,based on the finite element method,the related calculations of temperature rise and deformation are carried out.With the help of COMSOL finite element simulation software,based on linear and nonlinear model,the temperature rise and deformation distribution of optical components with different materials(fused silica and silicon)and irradiated by light beams with different shapes(Gaussian beam and annular flat-top spot)were solved.The effects of different parameters on the temperature rise and deformation of optical components are discussed.The research results show that nonlinear effects exist in the thermal,mechanical and optical absorption of optical components irradiated by high-power CW lasers.For example,based on this nonlinear model,when a fused silica sample with an absorptivity of 100 ppm was irradiated by a laser with Gaussian beam,if the nonlinear factors of physical parameters and temperature boundary conditions are not considered,there are a relative error of 16% of the maximum surface temperature rise and the relative error of 10% of peak-to-valley value of surface deformation.Finally,numerical calculations and experimental study of thermally induced birefringence are carried out.The temperature rise distribution of the Nd:YAG slab irradiated by pump laser was measured.The thermal conductivity of the sample,the heat transfer coefficient in the temperature boundary condition and the absorption coefficient of the sample were determined from the above results.Based on the related theory of birefringence,the thermally induced birefringence of Nd:YAG laser crystal irradiated by pump laser was solved by means of COMSOL finite element simulation software.The thermally induced birefringence was accurately measured by the cavity ring-down technique,which has been studied for a long time by our team,and the relevant photoelastic constant used in the calculation was determined at the same time.The numerical calculation and measurement results are analyzed and discussed.