Ranges of existence and stability of two-mode stimulated emission from a mode-locked ring laser with two-isotope active medium

The ranges of existence and stability of two-mode stimulated emission from a ring gas laser with a twoisotope active medium are investigated theoretically as a function of various laser parameters. The analysis is made using a complete system of amplitude and phase equations and the normal oscillation method. It is shown that a stable steady-state value of the difference between the phase shifts of the two modes in the opposite waves may lie in the interval (0, 2π) but need not be close to 0 or π. The actual value of this difference between the phase shifts is governed by the ratios of the backscattering coefficients and relative Q factors to the coefficients of the combination interaction of different modes of the opposite waves.