Diagrammatic representation of photon echoes and other laser-induced ordering processes in gases

Abstract

A simple diagrammatic approach to the description of laser-induced macroscopic ordering processes in gases is developed. We derive a set of simple rules which can be used to construct diagrams—each of which represents the macroscopic properties of a gaseous sample after it has been excited by a particular sequence of short, resonant, laser-excitation pulses. The features of the diagrams which signify various forms of laser-induced macroscopic ordering, e.g., photon echoes, grating echoes, stimulated echoes, standing-wave echoes, trilevel echoes, nonthermal velocity distributions, etc., are discussed. Important differences between the actions of traveling-wave and standing-wave excitation pulses are pointed out. The diagrammatic technique presented here for gases can easily be generalized to describe laser-induced macroscopic ordering in solids as well.