反射式扩束常用于大功率的激光发射装置，但在离轴状态下，仅仅控制多组镜片之间的相对距离并不能像透射式扩束一样顺利实现变倍。从扩束望远镜系统的失调状态得到启发，提出一种两片次镜切换变倍的光学方案，针对一束CO2激光器发出的直径为54 mm的激光束，完成了离轴工作时1.5倍和3.0倍两个档位的扩束光学设计。仿真结果证明了扩束功能的正确性，而且与主次镜相同曲率半径下同轴使用的失调望远镜系统的调制传递函数(MTF)曲线基本吻合，对离焦量进行补偿之后的成像效果能够达到衍射极限。

Reflective beam expanders are widely used for high-power laser launchers. However, compared with refractive expander, it is harder to realize zoom effects because of off-axis. This paper focuses on a new program, using one piece of main mirror and two different secondary mirrors to change the magnification of expanders, and a system is designed to expand a CO2 laser beam from 54 mm diameter to 81 mm (1.5×) and 162 mm (3.0×) in the state of off axis. The simulation results indicate that this kind of design is of great practicality with almost the same modulation transfer function (MTF) curves as a maladjusted telescope, having the same order of magnification with commonly used expanders. After compensating the defocus amount, the system′s imaging achieves the diffractive limit.