SEMI-CLASSICAL LASER THEORY IN THE STOCHASTIC AND THERMODYNAMIC FRAMEWORKS

The thermodynamic properties of the laser distribution in the steadily oscillating state are investigated to determine the minimum characteristic of the entropy production. First, the laser Langevin equation for five random variables is treated in the light of the stochastic calculus to deduce the photon-number rate equation n = - C+(n - nc) + [A/(1 + sn)](n-nA), where nn and n4 are the two constants of the fluctuation attributed to the noise forces subject to the usual fluctuation-dissipation theorem, with n4 < 0 for the inverted atomic population. We then combine the dynamics of the lasing mode with a model open system of the Lebowitz type with two reservoirs for which the entropy production σ(p) is expressed and made subject to a variational principle: The modified variation scheme, the same as Prigogine's local potential method, is shown to give the exact lasing distribution p as the optimum between two distributions of thermal type with temperatures far from each other. © 1979 Plenum Publishing Corporation.