说明：  设计半径为1mm的平面波经凸面曲率半径为25mm，中心厚度3mm的平凸透镜。用matlab仿真平面波在透镜几何焦平面上的聚焦光斑强度分布，计算光斑半径。并与理论光斑半径值进行对比，得出误差大小。（方法：采用波动理论，利用基尔霍夫—菲涅尔衍射积分公式。）
(Design a plano-convex lens with a plane wave radius of 1 mm and a convex curvature radius of 25 mm and a center thickness of 3 mm. Matlab simulates the intensity distribution of the focused spot on the geometric focal plane of the lens with a plane wave, and calculates the spot radius. The error is compared with the theoretical beam spot radius.)