Time-space self-compression of femtosecond laser pulses in air

Summary form only given.We have observed that a pulse temporal self-compression takes place during the filamentation process. Pulse durations have been measured inside the filament by time-resolved self-diffraction between two identical filaments. We show this effect by comparing the pulse duration recorded before and well beyond the onset of filamentation. To obtain precise information on the physical origin of temporal self-compression, we have performed a three-dimensional numerical simulation of the propagation of an intense femtosecond laser pulse through atmosphere.