Thermal blooming of a rapidly moving laser beam.

We have theoretically evaluated aspects of high speed thermal blooming and have found that refractive effects are negligible except for the case of a beam moving at transonic velocities. The density perturbation at Mach I is determined primarily by nonlinear flow field effects induced by heating of the atmosphere. Although the temperature perturbation is very small for a beam moving at sonic velocity, the density perturbation is not. It is approximately 2 orders of magnitude higher than the temperature perturbation. This large increase in the density perturbation is confined to a narrow range of Mach numbers that define a transonic flow in atmospheric propagation. Outside this transonic flow regime, thermal blooming is negligible.