激光传输模拟中基于衍射过程FFT算法的参量优化

Parameter optimization based on FFT algorithm in numerical simulation of laser propagation in turbulent atmosphere

为实现采用相位屏法正确模拟准直激光束经湍流大气的传输特性,根据湍流特性、抽样定理以及两屏间衍射过程FFT算法本身所决定的相邻两屏网格间距之间的关系,得出相位屏间距和网格间距确定网格数目最优取值的解析表达式,数值模拟高斯光束经自由空间和湍流大气传输的远场分布,网格数目取解析式求得的最优值848时,光束经自由空间传输的模拟结果与ABCD定律求得的解析结果完全一致;网格数目取836或860时,等效于光束通过偶数相位屏时被正透镜或负透镜阵列会聚或发散,削弱或夸大湍流大气对光束的影响,模拟结果出现严重偏差。

To correctly simulate laser propagation in turbulence with phase screen method, based on the turbulent atmosphere＇s property, the sampling principle and the grid intervals＇ relation between two adjacent screens determined by FFT, a formula to calculate the optimal value for grid number based on step distance and grid intervals is derived, and laser propagation in free space and turbulent atmosphere is simulated. It is shown that the simulation result for laser propagation in free space coincides with the theory result when grid number＇s value is 848 calculated by the given formula. Specifying grid number a smaller or lager value such as 836 or 860, it is equivalent to that light ray is converged or diverged by a convex lens arrays or a concave lens arrays when passing through even screens, which weaken or exaggerate turbulence＇s effect on propagation beam and generate erroneous simulation result.