Mechanisms of stimulated emission from molecular lasers in far infrared

A theoretical analysis is made of the physical processes in diatomic and polyatomic molecular lasers emitting in submillimeter and far infrared parts of the spectrum. The rotational relaxation is considered in detail for a system of diatomic molecules. Analytic functions are obtained for the distributions of populations of rotational levels in the presence of a source of rotationally excited molecules. Estimates obtained for the adiabatic range of the rotational spectrum indicate the possibility of building efficient lasers. The mechanisms of stimulated emission from polyatomic molecules are considered. The problems of establishing a population inversion of rotational levels of weakly asymmetric tops are discussed briefly. The laser emission due to vibration-rotational transitions is analyzed. Several specific laser action schemes are suggested for water vapor and these should make it possible to achieve high-power cw emission.