Propagation of High Energy Laser Beams Through Atmospheric Stagnation Zones

Stagnation zones, i.e., regions in which the effective wind velocity is zero, can greatly enhance the thermal blooming of high-energy laser (HEL) beams in the atmosphere. An expression for the Strehl ratio of a focused HEL beam propagating through a stagnant absorbing region is derived. The propagation of a HEL beam in a maritime atmosphere is numerically modeled in a fully three-dimensional and time-dependent manner. The beam is focused onto a remote target, and a stagnation zone is created by slewing the laser in the direction of the wind. The laser power delivered to the target is calculated as a function of slew rate. For the parameters considered, it is found that a stagnation zone near the laser source has little effect on the propagation efficiency while a stagnation zone near the target can significantly reduce the power on the target. The original document contains color images. Prepared in collaboration with Icarus Research Inc., Bethesda, MD.