相位不连续点数目随湍流强度的变化

Variation of-Phase Branch Point Number with Turbulence Strength in Laser Propagation through Atmosphere

激光在湍流大气中传输时,若光束波前中出现相位不连续点,自适应光学的校正能力将明显降低,利用4维程序计算了激光在大气中传输时产生的相位不连续点的数目。通过选取不同的相位屏数、计算网格和网格间距,得到了畸变光场中产生的相位不连续点的数目随湍流强度变化的过程,即:相位不连续点的数目随湍流的增强有一个从无到有,从缓慢增加到近似线性的急剧增加,而后又缓慢增加,最后趋于饱和的变化过程。另外,在不同的传输条件下,相位不连续点的数目及其变化存在很大差异。

When branch points are present in laser beam wavefront during the propagation in turbulence, the adaptive-optics system for atmosphere turbulence compensation will be degraded greatly. The number of branch points was computed by four-dimensional code. By choosing different phase screen number, grid size and grid step, the variation of branch point number with turbulence strength in distorted optical fields was emulated. The result indicates that branch points cannot be detected in the region of weak turbulence. In the intermediate region between the weak and the strong turbulences, the branch points begin to appear, and the number of branch points grows rapidly at the outset of this region, almost linearly. When the turbulence strength continues growing, the rapid growth of the branch point number is replaced by a slower but nonlinear increase. In the end, the branch point number reaches a saturation state. In addition, the branch point number and its evolvement are different in different propagation conditions.