Mode competition in lasers with homogeneous line broadening

This paper deals with the general concepts of mode interaction in the case of homogeneous line broadening. A simple analysis of rate equations for the radiation fields of the operating modes based on a somewhat phenomenological picture describes the asymptotic values of the mode intensities. Conditions are deduced in which mode interaction leads to the survival of only the most strongly excited mode, although initially all competing modes are above threshold. It is argued that this theory holds for CO
2
lasers. As examples we calculate competition between 1) the TEM
00
and TEM
01
mode and 2) two rotational transitions.