Nonlinear-optical imaging and tagging of atoms and molecules in plasmas and gas flows

Summary form only given.Recently, much attention has been focused on the development of experimental techniques for the visualization of spatial distributions of atoms and molecules in plasmas and flames and velocity profiles in gas flows. In this paper, we discuss the possibilities of two nonlinear-optical techniques that use Raman resonances-coherent hyper-Raman four-wave mixing and Raman excitation + laser-induced electronic fluorescence for plasma imaging and flow tagging.