说明：   用基于 Matlab 的小容量 FFT (比如 256×256)程序，将取样窗口划分为 若干个全等的小矩形,对每个小矩形内离散点的复振幅作 FFT 变换,然后将所有变 换结果叠加，再乘以复数相位因子,相当于对整个物面上点进行菲涅耳衍射计算， 利用这种方法可以迅速的实现高精度的轴对称傍轴光学系统中的激光衍射计算
(With a small volume based on Matlab FFT (eg 256 × 256) procedure to sample window divided into a number of small identical rectangles, each small rectangle of discrete points within the complex amplitude for the FFT transform, and then transform the results of all the superposition multiplied by the complex phase factor, the equivalent point on the object plane Fresnel diffraction calculation, the use of this method can rapidly achieve high-precision optical system axis of symmetry in the paraxial calculation of laser diffraction)