SPECTRAL AND SPATIAL MODIFICATIONS TO AN INTENSE 1-MU-M LASER-PULSE INTERACTING WITH A DENSE ARGON GAS

Reported is the spectral shifting observed when a approximately 1 ps, 1 mum laser pulse is focussed into a cell containing argon at pressure s from 0-10 bar. Focal intensities of 1-5 X 10(15) W cm-2 would be exp ected in vacuum for the f/8 focussing used. Instead evidence is found in the spectra of a significant decrease in the focal intensity reache d when higher gas pressures are used. For the first time the spatial d istribution of the shifted spectra is investigated. Spectral shifts ar e found to increase off-axis in the transmitted beam profile. The dist ributions show many peaks and minima and contain much extra detail. A two-dimensional numerical propagation model shows good general agreeme nt with the experimental results.