激光在云中传输时会出现能量降低、角度弥散、时间展宽和空间分散等现象。 利用蒙特卡洛法研究了云的高度和厚度对激光下行传输的影响。在云厚度固定、云高度变化和云高度固定、 云厚度变化两种情况下, 分别仿真了激光透过云下行传输到海平面时的能量、角度、时域和空域分布。 结果表明, 当云厚度固定时, 随着云高度的增加, 到达海平面的激光脉冲半峰全宽和光斑尺寸明显增加, 但是能 量和角度分布基本保持不变; 当云高度固定时, 随着云厚度的增加, 到达海平面的激光脉冲能量降低, 角度 分布先弥散后趋于稳定, 半峰全宽增加, 光斑尺寸先增大后趋于稳定。该研究为评价光通信系统的性能提 供了一定的参考。

When a laser pulse propagates through a cloud, the phenomena such as energy decay, angle diffusion, temporal broadening and spatial dispersion may occur for it. The Monte Carlo method is used to study the effect of cloud altitude and thickness on laser downward transmission. The energy, angular, temporal and spatial distribution values of a laser pulse after it transmits downward to the sea level through a cloud are simulated respectively in both a situation that the cloud thickness is fixed while the cloud altitude is changing and a situation that the cloud altitude is fixed while the cloud thickness is changing. The result shows that when the cloud thickness is fixed, the Full Width Half Maximum (FWHM) and spot size of the laser pulse at sea level increase obviously with the increase of the cloud altitude. However, its energy and angular distribution values remain unchanged. When the cloud thickness is increasing while the cloud altitude is fixed, the energy of the laser pulse at sea level decreases, its angular distribution firstly diffuses and then trends to be stable, its FWHM increases and its spot size firstly increases and then trends to be stable. This research is of a referential value to the performance evaluation of optical communication systems.