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 pressures from 0-10 bar. Focal intensities of 1-5 X 10(15) W cm-2 would be expected in vacuum for the f/8 focussing used. Instead evidence is found in the spectra of a significant decrease in the focal intensity reached when higher gas pressures are used. For the first time the spatial distribution of the shifted spectra is investigated. Spectral shifts are found to increase off-axis in the transmitted beam profile. The distributions show many peaks and minima and contain much extra detail. A two-dimensional numerical propagation model shows good general agreement with the experimental results.