Simulation and Compensation Technology of Thermal Lens Effect in High-Power CO<sub>2</sub> Laser

高功率CO2激光器广泛应用于加工处理等各个领域。随着功率增大，热效应是影响高功率CO2激光光束质量的主要原因。文章主要针对CO2激光器中高功率导致的热透镜效应，将有限元方法与光线追踪相结合，建立了元件/模块附近空气的温升和对流模型，分析了光学元件与附近气体之间的传热过程。利用该模型，探究了光学元件的热变形及其对光学系统的影响。结果表明，ZnS、ZnSe和金刚石透镜在5 kW功率下的形变量分别为13.7 μm、1.02 μm、0.00291 nm。随着功率增大到50 kW，ZnS透镜形变更明显，分别是204 μm、15 μm、0.0288 nm。在此基础上，研究基于波前优化技术，设计了一种补偿透镜来补偿热效应导致的波前畸变。结果表明，球面镜和非球面镜均能对波前畸变进行有效补偿。在高功率下，将三种透镜的RMS值分别从1.4773λ、5.2824 λ、4.9372 × 10−6 λ优化到0。偶次非球面镜补偿后的波前面型更平坦，能够更有效地校正高阶像差。High-power CO2 lasers are widely used in various fields, such as processing. As the power increases, thermal effects are the main reason affecting the quality of high-power CO2 laser beams. This article mainly focuses on the thermal lens effect caused by high power in CO2 lasers. By combining the finite element method with ray tracing, a temperature rise and convection model of the air near the component/module is established, and the heat transfer process between the optical component and the nearby gas is analyzed. Using this model, the thermal deformation of optical components and its impact on optical systems were analyzed. The results showed that the deformation of ZnS, ZnSe, and diamond lenses at a power of 5 kW were 13.7 μm, 1.02 μm, and 0.00291 nm, respectively. As the power increased to 50 kW, the deformation of ZnS lenses changed significantly, reaching 204 μm, 15 μm, and 0.0288 nm, respectively. On this basis, a compensating lens is designed based on wavefront optimization technology to compensate for wavefront distortion caused by thermal effects. The results indicate that both spherical and non-spherical mirrors can effectively compensate for wavefront distortion. At high power, optimize the RMS values of the three lenses from 1.4773 λ, 5.2824 λ, and 4.9372 × 10−6 λ to 0, respectively. The wavefront shape after even non-spherical mirror compensation is flatter, which can more effectively correct high-order aberrations.