Self-trapping, self-focusing, and filamentation in air

Summary form only given. There have been numerous observations of self-trapping of ultrashort laser pulses in filaments. This paper presents an investigation of filamentation in air at 248 nm. At this short wavelength, ionization of air proceeds by a multiphoton process (rather than tunnel ionization) that can be quantified independently of the filamentation process. Using the measurements of Losev and Soskovs for the photoionization rate, we find a filament diameter of 200 /spl mu/m, which matches our experimental observations at that wavelength. The characteristic attenuation length for the corresponding "hollow waveguide" is now 5 m, still shorter than our experimental observation, but at least of the same order of magnitude.