Femtosecond and picosecond ultraviolet laser filaments in air: experiments and simulations

We report a study of the long-range self-guided propagation of intense femtosecond and picosecond UV laser pulses in air. Measurements of the laser beam profile along the propagation axis together with the ionization rate. the pulse temporal profile and power spectrum provide a comprehensive image of the UV filamentation process and its characteristics. Self-guiding is shown to subsist in both fs and ps cases, with a robust filament propagating over several meters in air. Stable filamentation is accompanied by an important restructuring of the pulse temporal profile. Complementary numerical simulations, using a three-dimension propagation code. are compared to the experimental results. The simulations reproduce most experimental observations. allowing for a better understanding of the phenomena involved in this unique propagation mode. (C) 2001 Published by Elsevier Science B.V.