Two-mode emission from a ring gas laser with a twoisotope active medium

A theoretical analysis is made of steady-state two-mode (two- and four-wave) emission from a ring gas laser with a two-isotope active medium. The interaction coefficients of traveling waves are calculated for two longitudinal linearly polarized modes. Two cases are considered: Modes polarized in one direction and at right-angles to one another. The limits of stability of the two-mode (two- and four-wave) emission are investigated as a function of the following parameters of a ring gas laser: mode spacing, positions of modes on the gain curve, longitudinal dimensions and relative positions of tubes with the active medium, lifetimes and total momentum of the active levels, and width of the spontaneous emission line.