Mid-infrared laser beam scintillation study

摘要

We present results of propagation measurements (over 545 m and 5.7 km paths) carried out with a pulsed laser beam (12 ns pulse width) at a wavelength of 3.7 um under sunny and cloudy atmospheric conditions. The objective of the study was to evaluate, for these distances, the effects of atmospheric turbulence on the deposited power levels achievable on targets having diameters of a few tens of mm. Measurements of scintillation levels, probability distributions, and durations of intervals where the power level stays continuously above or below its mean value were carried out. The results show that, for all atmospheric conditions encountered, the lognormal probability distribution can be used to correctly describe the probability of obtaining some given power levels. Also, the statistics of continuous time intervals spent above and below the mean power are shown to follow an exponential probability distribution. Experimental results relating the mean durations of these intervals to the scintillation levels, the wind speeds, and the probability distribution of collected power levels are also presented. These results could help in determining the source power required to ensure a given level of exposure on targets with a pre-determined probability, taking into account the reaction times of the targets.