为了实现波导CO2激光调Q脉冲输出, 需要搭建半外腔激光器以在谐振腔内插入Q开关。实验研究了波导纵横比m=2的半外腔矩形波导CO2激光器的输出功率与谐振腔光学结构参数之间的关系, 对比了平面反射镜紧贴波导口激光器的输出功率, 得到谐振腔模式耦合进入波导口的损耗与谐振腔全反镜曲率半径R以及全反射镜至波导口的距离d的关系。基于菲涅耳衍射积分理论, 采用变步长辛普森算法理论计算了m=2的矩形波导谐振腔耦合效率与R、d之间的关系。基于实验及理论结果, 得到了适合高纵横比矩形波导CO2激光器半外腔搭建的两个耦合效率较高的谐振腔光学及结构参数：d=10 mm、d=R的位置, 并且R越大这两个位置对应的耦合效率越高。

In order to achieve Q-switched pulse output of the CO2 waveguide laser, a half-external cavity laser is necessary to insert the Q switch in the resonator. We study the relationship between the output power of the rectangular waveguide half-external cavity CO2 laser with the waveguide aspect ratio m=2 and the optical structural parameters of the resonator. We compare the output powers of the laser whose waveguide port clings to the plane mirror, and obtain the relationship between the loss generated by the resonant cavity mode coupling to the waveguide port and the radius of the total reflection mirror R, and the distance between the total reflection mirror and the waveguide port d. Based on the Fresnel diffraction integral theory, the relationship between the coupling efficiency of the resonator and R, d when m =2 is calculated with the Simpson algorithm variable step length theory. The results show that d=R and d=10 mm are two optical and structural parameters which are suitable for the rectangular waveguide half-external cavity CO2 laser with a high aspect ratio, where larger R will induce higher coupling efficiency.