Recurrent femtosecond pulse collapse in air due to plasma generation: numerical results

In this report we present numerical simulations of nonlinear pulse propagat ion in air to elucidate the physical mechanism underlying the experimentall y observed long distance propagation of filaments. Simulations of the nonli near Schrodinger equation for the electromagnetic field coupled to the elec tron plasma generated via multiphoton ionization yield a very dynamic pictu re of long distance propagation in which pulses form, are absorbed, and sub sequently are replenished by new pulses, thereby creating the illusion of o ne pulse, of energy much less than the input, which is self-guided. Moreove r, the evolution of the field and plasma display rich spatio-temporal struc tures with strong gradients, eventually leading to the breakdown of the num erics. Adaptive mesh refinement methods are explored to overcome these diff iculties and to address the onset and recurrence of multiple light filament s during the long distance propagation of intense femtosecond infrared puls es in air and point out the features which are common to strong turbulence in other physical systems. The space-time collapse events drive the turbule nce here, and plasma defocusing, not dissipation, is the dominant mechanism regularizing the collapse. (C) 2001 IMACS. Published by Elsevier Science B .V. All rights reserved.