说明：  有一平面镜和曲率半径为 的凹面镜，画出光束发散角与腔长 的关系曲线。 设计要求：（1）具有友好输入输出界面； （2）可输入不同凹面镜曲率半径值，查看结果变化情况。
(Plane mirror and one has a radius of curvature of the concave mirror, draw the beam divergence angle and cavity length curve. Design requirements: (1) friendly input and output interface (2) may enter a different value of the radius of curvature concave mirror to see the results of the changes.)