Abstract

Femtosecond laser pulses with an energy of a few mJ can be compressed spatially through Kerr self-focusing in air over a distance of a few meters.¹ Under appropriate initial conditions, the pulse propagates beyond the self-focusing distance over several tens of meters in the form of a stable filament with a diameter of a few hundred microns.^2-4 We have observed that a pulse temporal self-compression also takes place during the filamentation process. Pulse durations have been measured inside the filament by time-resolved self-diffraction between two identical filaments. Figure 1 shows this effect by comparing the pulse duration recorded before and well beyond the onset of filamentation.

© 1998 Optical Society of America