Femtosecond and picosecond ultraviolet laser filaments in air: experimentsand simulations

We report a study of the long-range self-guided propagation of intense femt osecond and picosecond UV laser pulses in air. Measurements of the laser be am profile along the propagation axis together with the ionization rate. th e pulse temporal profile and power spectrum provide a comprehensive image o f the UV filamentation process and its characteristics. Self-guiding is sho wn to subsist in both fs and ps cases, with a robust filament propagating o ver several meters in air. Stable filamentation is accompanied by an import ant restructuring of the pulse temporal profile. Complementary numerical si mulations, using a three-dimension propagation code. are compared to the ex perimental results. The simulations reproduce most experimental observation s. allowing for a better understanding of the phenomena involved in this un ique propagation mode. (C) 2001 Published by Elsevier Science B.V.