基于Mie散射的CO_2激光大气传输特性测量

为了更准确地计算大气透过率,在Mie散射理论基础上,分析了雷达系统设计中需考虑的大气透过率的经验计算公式,指出了该经验公式的不足。考虑大气分析软件MODTRAN自身的优点,采用经验公式和软件计算相结合的方式计算大气透过率,给出了MODTRAN计算结果的修正表达式。在该理论指导下,进行了CO2激光大气传输实验。由于没有考虑大气湍流,理论计算和实验结果存在一定偏差,但不影响本文方法的实用性。实验测量显示,激光器出口处光斑能量抖动比为6.18%,而在50m和1km处能量抖动比分别为8.3%和50.2%,表明随着传输距离增加,能量抖动比增大。除掉激光器本身输出能量抖动外,在50m和1km处由大气传输造成的能量抖动比分别为2.12%和44.02%。实验结果提示,水平传输1km时能量抖动已相当剧烈,所以对更远距离的激光传输,自适应光学补偿显得尤为重要。

Measurement of CO2 laser atmospheric transmission property based on Mie scattering

In order to calculate the atmospheric transmittance more correctly, the empirical expression of atmosphere transmittance which should be considered in the design of lidar systems based on Mie theory was analyzed in this paper, and the disadvantage of the empirical expression was demonstrated. In consideration of the merits both the empirical expression and MODTRAN software, they were combined to calculate the atmospheric transmittance. As a result, a modified transmittance expression was achieved. The atmospheric transmittance experiments of CO2 laser were completed under the theory above. The actual results and the theory have some differences without considering the atmosphere turbulence, but there is no impact on the practicability of the theory. The experimental results show that the energy drift ratio of the laser is 6.18% at the output window, and 8.3% and 50.2% at the distances of 50 m and 1000 m, respectively, which means the ratios increase with the enlargement of distance. The main reason of the drift is the atmospheric transmission according to the experimental environments. Excluding the drift ratios at the output window of the CO2 laser, the energy drift ratios are 2.12% and 44.02% at 50 m and 1 000 m, respectively. The experimental results demonstrate that the energy twitter has been so fiercely at 1 000 m, therefore, the adaptive optics compensation is very important in the long-range atmospheric transmission.