NONLINEAR SELF-CHANNELING OF HIGH-POWER LASERS THROUGH TURBULENT ATMOSPHERES
DiComo, Gregory Putnam
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A variety of laser applications have been considered which depend on long-distance atmospheric propagation of the beam to attain practical utility. The effectiveness of these applications is limited to some extent by beam distortions caused by atmospheric optical turbulence. Often the limiting factor is the instantaneous beam spreading due to turbulence, which makes it impossible to create a small laser spot at the receiver. In the absence of turbulence, laser beams of sufficient peak power propagating in atmosphere have been shown to undergo nonlinear self-guiding, in which the beam size remains constant over multiple Rayleigh lengths. Recent research suggests that self-guiding beams of sufficiently small diameter might exhibit resistance to turbulent spreading, in a propagation mode known as nonlinear self-channeling. Presented here is an experimental demonstration of such self-channeling through an artificially controlled turbulent atmosphere, with investigation into the region of parameter space over which it can occur. This research makes use of a distributed-volume turbulence generator and long propagation ranges at the Naval Research Laboratory and the Air Force Research Laboratory in order to produce a controlled propagation environment suitable for the study of high-power beams. Nonlinear self-channeling is found to resist the diffractive effects of turbulence, with its effectiveness decreasing significantly as the inner scale of turbulence decreases below the size of the beam.