PANORAMIC 2-DIMENSIONAL VISUALIZATION OF THE SPATIAL-DISTRIBUTION OF THE ATOMIC AND IONIC COMPONENTS OF A LASER-PLASMA BY THE METHOD OF COHERENT 4-PHOTON SPECTROSCOPY

An experimental method is proposed for two-dimensional mapping of the relative populations of excited states of atoms and ions in a low-temp erature optical-breakdown plasma. The method is based on a technique o f coherent four-wave mixing combined with a hyper-Raman resonance. A s tudy is reported of the possibility of obtaining information on the sp atial distribution of the excited-state populations of atoms and ions from two-dimensional maps of the four-wave mixing signal taking accoun t of the phase mismatch and of one-photon absorption. Conditions were found experimentally for the four-wave mixing in a plasma in a phase-m atched regime without a significant influence of the one-photon absorp tion.