Theory of gain and saturation for collision-induced lasing transitions

Abstract

Theoretical expressions are given for the inversion density, small-signal-gain coefficient, and saturation-energy flux which pertain to stimulated collision-induced emission, that is, the free-free and free-bound dipole emission from unbound excited states formed during a collision of an atomic metastable species and another atom. The probability of stimulated emission during a collision is assumed to remain much less than unity so that a Maxwellian velocity distribution of excited atoms is maintained. The gain and saturation are described in terms of a profile function k (ν), a frequency-dependent two-body rate coefficient per unit frequency. The final expressions are analogous to those for a homogeneously broadened two-level atom. The theory is applied to the collision-induced green continuum from oxygen 1S0 in argon.