Experimental Study for the Relative Humidity Effect on Laser Transmission in Air

Abstract

Laser weaponization had been considered impossible for decades because laser essentially has light properties such as refraction, reflection, scattering, and absorption. However, several weapon projects are underway due to technological advances. Hence, it is important to accumulate experimental data on laser transmission in the atmosphere. In this thesis, the tendency of the laser transmission in the humid air is statistically summarized through numerous repetitive experiments. Nd:YAG laser beam was propagated in the moist air of the cylinder. The RH of the air in the cylinder was changed in every experiment. The extinction coefficients were measured to determine the transmission. The measured coefficients were compared with the simulation results of the U.S. Air Force to ensure the reliability of this study. The results show a similar tendency of the laser transmission without significant change up to 48 ~ 70 % RH. The transmission decreases sharply as RH increases from 70 ~ 100 % RH. Various conditions were changed to reduce the influence on the divergence of the laser itself. Conditions are the distance of propagation, collimation, and the mode of the laser. The extinction coefficients were measured to be 5-20 times higher than those of the simulation. Different attempts were performed, but the results were still high. The expected reason is the difference between the air in the experiments and that of the simulation. Further study is required to make clear this question.