Time Resolution of Collapse Events During the Propagation of Ultraviolet Light Filaments

<p>Long distance propagation or filamentation of short intense laser pulses is 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 femtocecond 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 work. 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 claiming UV filamentation is shown to be artificially limited by numerical parameters.</p><p>This work has been selected by scholars as being culturally important and is part of the knowledge base of civilization as we know it. This work was reproduced from the original artifact and remains as true to the original work as possible. Therefore you will see the original copyright references library stamps (as most of these works have been housed in our most important libraries around the world) and other notations in the work.</p><p>This work is in the public domain in the United States of America and possibly other nations. Within the United States you may freely copy and distribute this work as no entity (individual or corporate) has a copyright on the body of the work.</p><p>As a reproduction of a historical artifact this work may contain missing or blurred pages poor pictures errant marks etc. Scholars believe and we concur that this work is important enough to be preserved reproduced and made generally available to the public. We appreciate your support of the preservation process and thank you for being an important part of keeping this knowledge alive and relevant.</p>