Multimode oscillation of a cw unstable-cavity CO2 laser with a nonstationary active medium

A method of analysis of lasing at several transverse modes in a nonstationary active medium with substantial optical inhomogeneities is developed. It is based on the assumption that the round-trip transit time for radiation in the resonator is much shorter than the characteristic time of a change in the spatial distributions of the gain and refractive index. The nonstationary oscillation of a transverse-flow CO₂ laser is analysed by this method in a two-dimensional approximation in the case when the vibrational excitation of an active medium at the cavity input changes in time and phase distortions move.