TIME-RESOLVED SPECTRAL AND SPATIAL DESCRIPTION OF LASER-INDUCED BREAKDOWN IN AIR AS A PULSED, BRIGHT, AND BROAD-BAND ULTRAVIOLET-VISIBLE LIGHT-SOURCE

The optical breakdown induced in air at atmospheric pressure by Nd:YAG Q-switched laser pulses is studied in terms of the spectral features of the emitted radiation in the wavelength range 180-850 nm during the first 200 ns after the laser pulse onset. During the plasma build up, radiation emission features intense, broadband, and structureless ult raviolet-visible spectra before the appearence of atomic lines on the microsecond scale. Also, the emitting plasma kernel, imaged during the buildup and decay stages in the early tens of nanoseconds, turns out to have a size of similar to 0.3 mm and a volume of similar to 0.02 mm (3). The coupling of direct emission data and broadband absorption mea surements allowed us to retrieve peak values of electron temperature a bove 100,000 K and of an optical depth of the order of unity, under th e assumptions of local thermodynamic equilibrium and a homogeneous ker nel. The simultaneous occurrence of such temporal, spatial, and spectr al features of the plasma kernel suggests its exploitation as a pulsed , bright, and broadband ultraviolet-visible light source. (C) 1998 Opt ical Society of America.