Self-guiding of IR femtosecond laser pulses in air: experiments versus simulations

Summary form only given. There is presently a considerable interest in understanding the propagation of intense femtosecond laser pulses through the atmosphere. Self-guided IR laser beams with high peak power forming an intense filament over long distances have been reported by several groups. On the other hand, various attempts at modeling this phenomenon have been proposed, either by solving numerically nonlinear Schrodinger-like systems or by using more analytical approaches. However, although there is a wide consensus on the physical effects sustaining this unusual propagation, controversies still remain about the detailed explanation of the observed features. They partly originate from the fact that experiments are usually realized with pulses having an input transverse power exceeding by far the critical power, P/sub cx/, for self-focusing, whereas the simulations are mostly limited to powers close to P/sub cx/, which require considerably less computational time. We present a systematic study of the propagation of femtosecond IR pulses exhibiting a single transverse mode within a well-defined geometry, with pulse peak powers above critical. Emphasis is laid on precise measurements of the length of the self-guided filament and its inner energy, the power spectrum and the density of electrons liberated in the trail of the pulse. These data are compared in detail with results from a numerical code, which involves the main ingredients for describing ultrashort pulse propagation in air.