APPLICATION OF COHERENT 4-WAVE-MIXING FOR 2-DIMENSIONAL MAPPING OF THE SPATIAL-DISTRIBUTION OF EXCITED ATOMS IN A LASER-PRODUCED PLASMA

An experimental technique for the two-dimensional mapping of the relat ive populations of excited states of atoms and ions in a low-temperatu re plasma of optical breakdown is developed on the basis of coherent f our-wave mixing (FWM) with hyper-Raman resonances. The possibility to extract information concerning the spatial distribution of the populat ions of excited atomic and ionic states from two-dimensional maps of t he FWM intensity allowing for phase mismatch and one-photon absorption is considered. Conditions when FWM in a plasma occurs in the phase-ma tched regime and is not subject to a considerable influence of one-pho ton absorption are experimentally determined. (C) 1997 Elsevier Scienc e B.V.