A. James Clark School of Engineering
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Item NONLINEAR SELF-CHANNELING OF HIGH-POWER LASERS THROUGH TURBULENT ATMOSPHERES(2018) DiComo, Gregory Putnam; Antonsen, Thomas; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)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.Item EFFICIENT SIMULATION OF ELECTRON TRAPPING IN LASER AND PLASMA WAKEFIELD ACCELERATION(2009) Morshed, Sepehr; Antonsen, Thomas M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma based laser Wakefield accelerators (LWFA) have been a subject of interest in the plasma community for many years. In LWFA schemes the laser pulse must propagate several centimeters and maintain its coherence over this distance, which corresponds to many Rayleigh lengths. These Wakefields and their effect on the laser can be simulated in the quasistatic approximation. The 2D, cylindrically symmetric, quasistatic simulation code, WAKE is an efficient tool for the modeling of short-pulse laser propagation in under dense plasmas [P. Mora & T.M. Antonsen Phys. Plasmas 4, 1997]. The quasistatic approximation, which assumes that the driver and its wakefields are undisturbed during the transit time of plasma electrons, through the pulse, cannot, however, treat electron trapping and beam loading. Here we modify WAKE to include the effects of electron trapping and beam loading by introducing a population of beam electrons. Background plasma electrons that are beginning to start their oscillation around the radial axis and have energy above some threshold are removed from the background plasma and promoted to "beam" electrons. The population of beam electrons which are no longer subject to the quasistatic approximation, are treated without approximation and provide their own electromagnetic field that acts upon the background plasma. The algorithm is benchmarked to OSIRIS (a standard particle in cell code) simulations which makes no quasistatic approximation. We also have done simulation and comparison of results for centimeter scale GeV electron accelerator experiments from LBNL. These modifications to WAKE provide a tool for simulating GeV laser or plasma wakefield acceleration on desktop computers.