Interaction of longitudinal oscillation modes emitted by a gas laser with a rapidly decaying lower level

A modification of the Lamb equations, suitable for fairly high saturation levels, is proposed for lasers with a rapidly decaying lower level. The interaction between modes is divided arbitrarily into competition and interaction proper. The latter governs the phase relationships between the fields of different modes and can be identified because of the smallness of the terms responsible for this interaction. If only the competition is allowed for, the system of equations for the field amplitudes always has a unique steady-state stable solution. However, there are conditions when the interaction must be allowed for in spite of its smallness. In this case we can have conditions when the laser action is accompanied by a continuous spontaneous pumping of the energy between different modes.