Title of Dissertation: HIGH POWER NONLINEAR PROPAGATION OF LASER PULSES IN TENUOUS GASES AND PLASMA CHANNELS

The nonlinear propagation over long distances of moderate intensity laser pulses in tenuous gases is studied. The dynamics of these pulses will be affected by nonlinear focusing and dispersion due to the background gas, and by plasma induced refraction and dispersion. Laser propagation is studied numerically using the simulation code WAKE. Different phenomena are found for different regimes of peak input power. For powers near the critical power, temporal pulse narrowing and splitting due to phase modulation and group velocity dispersion is seen. For slightly higher powers, plasma generation and the formation of a trailing pulse, which is guided off axis by plasma refraction and nonlinear gas focusing, is observed. For even higher powers, the laser pulse is partially trapped by the plasma and then exhibits a form of self-interference. The processes affecting the spectrum of the pulse is also studied. Among these are self-phase modulation, nonlinear self-focusing, plasma generation, and group velocity dispersion. The combination of these factors leads to an asymmetric spectrum. If group velocity dispersion cannot arrest nonlinear self-focusing, self