STABLE SELF-CHANNELING OF INTENSE ULTRAVIOLET PULSES IN UNDERDENSE PLASMA, PRODUCING CHANNELS EXCEEDING 100 RAYLEIGH LENGTHS

Spatially confined propagation of high-power subpicosecond (similar to 270-fs) ultraviolet (248-nm) pulses has been experimentally studied i n cold underdense plasma. The observed channels were longitudinally un iform, were approximately 1.4 mu m in diameter, and persisted for a le ngth of 3-4 mm, a distance exceeding 100 Rayleigh ranges. X rays with a quantum energy > 0.5 keV were also detected from the zone of propaga tion in coincidence with the channel formation. The occurrence of self -channeling with the rapid formation of a stable, extended, and longit udinally homogeneous filament is in qualitative agreement with a theor etical picture involving relativistic and charge-displacement nonlinea rities.