为了提高传统球面镜腔3kW射频板条CO2激光器光束质量, 设计了新型抛物面镜负支非稳-波导混合腔; 结合标量光束的瑞利-索末菲衍射理论与特征向量法, 研究了大菲涅耳数下镜面类型对非稳波导混合腔光场传输特性的影响; 利用矩形波导理论、1维近似分析得出了波导传输损耗及偏振情况。结果表明, 将非稳方向输出镜和尾镜改为与光轴交点处曲率半径为R1=951.32mm和R2=1088.68mm的抛物镜面, 能够避免尾镜漏光, 可有效改善模式鉴别特性; 常用波导电极镀膜材料中, 镀铝电极内波导方向传输损耗最小, 传输光场为x偏振的EH1模。采用电极镀铝的抛物面非稳波导腔能够降低损耗、提升光束质量。

In order to improve the beam quality of traditional spherical mirror cavity in 3kW radio frequency slab CO2 laser, a new negative branch unstable-waveguide hybrid resonator with parabolic mirrors was designed. Based on Rayleigh-Sommerfeld diffraction theory for scalar beam, the influence of mirror type on optical field transmission characteristics of unstable hybrid waveguide cavity in the condition of large Fresnel number was studied. Based on rectangular waveguide theory and 1-D approximation, the waveguide propagation loss and polarization were analyzed. The research shows that, in the unstable direction, rear mirror and output mirror with paraboloid of curvature radius R1=951.32mm, R2=1088.68mm can avoid light leak of rear mirror and effectively improve the mode identification characteristic. Among common waveguide electrode coating materials, aluminum electrode can supply minimum waveguide propagation loss and transmission optical field is x polarization EH1 mode. Using unstable-waveguide hybrid resonator with parabolic mirrors whose electrodes are coated with aluminum can reduce loss and improve beam quality.