Date of Award

10-11-2007

Document Type

Thesis

Degree Name

Master of Science in Applied Physics

Department

Department of Engineering Physics

First Advisor

Thomas A. Niday, PhD

Abstract

Long distance propagation, or filamentation, of short, intense laser pulses is suggested to be possible through the balance of two effects: self-focusing, when a nonlinear index of refraction of air is induced by high intensities, and de-focusing, due to the plasma created by the pulse. Applications for filamentation include areas such as remote sensing and directed energy. A split-step spectral propagation simulation is used to model the behavior of a high intensity ultraviolet laser pulse propagating through air. Convergence of femtosecond duration collapses that form on the leading edge of the pulse in the time domain is achieved with an increase in the multi-photon ionization coefficient. Through an analysis of the relative sizes of each term in the propagation equation, a lack of plasma present at the leading edge of the pulse is found to cause these collapses. Results for a more recent value of the electron-positive ion recombination rate are compared to results from a higher value used in previous works. A linear stability analysis shows inherent instability of the pulses in all cases. The inclusion of group velocity dispersion is shown to increase stability at high temporal frequencies except at zero spatial frequencies. A run similar to an experiment that produced UV filamentation is shown to propagate 70 cm without exceeding numerical limitations.

AFIT Designator

AFIT-GAP-ENP-08-M03

DTIC Accession Number

ADA476947

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