为了与大面积放电增益区匹配,千瓦级射频板条CO2激光器采用大菲涅尔数的条状离轴负支共焦非稳腔,其输出模式是对整个输出平面上光场分布在特定区间的截断,对应的傅里叶谱(空间频率)会无限展宽。通过改进的虚源法求得其输出平面的场分布,然后通过对输出光场的傅里叶谱的分析,研究了条状离轴负支共焦非稳腔的两个主要参数——有效菲涅尔数Neq以及几何放大率M对输出光束质量的影响。数值模拟的结论显示输出光束的质量只与M相关,随着M的绝对值的增加,光束质量会呈现周期振荡式的下降,周期约为0.05。

In order to match the size of the large gain area, the strip negative branch confocal unstable resonator is employed in kW RF-excited slab CO2 laser. The output beam is the certain truncation from the mode distribution on the output plane, the corresponding Fourier spectrum (space frequency) expand to infinite. In this paper, the mode on the output plane is calculated by the modified virtual source method, the effect of the parameters of resonator: the equivalent Fresnel number Neq and the geometric magnification M on the output beam quality is analyzed by its Fourier spectrum. The numerical results show that the output beam quality is only relevant to M, it will decline periodically as the absolute value of M increase, and the period is about 0.05