Semiclassical theory of stability in a laser using a generalized entropy

The stability criteria in the pumping and lasing states in a cw solid-state laser are investigated using the semiclassical theory of the multimode laser. The model admits of one (trivial) steady state corresponding to thermal equilibrium, for which an $N$-body principle of minimum-entropy production may be obtained the entropy production serving as a Lyapounov function in this case. The other (multiple) steady states are far from thermal equilibrium. It is possible to construct an $N$-body Lyapounov function in the general, multimode case for these states within the framework of the rate approximation. Near equilibrium, the linear thermodynamics of the multimode laser are developed with the entropy production.