Theory of open systems: II. An application; The single-mode laser

Abstract The method given in part I of the present paper is applied to the single-mode laser model. The treatment is based on two coupled equations for the Glauber distribution function of the field and for another distribution, which is linked in a simple way to the atomic inversion. It is shown that such equations are the operator analogue, in the Schrodinger picture, of the semi-classical equations of the laser. The analysis leads to a quantum-mechanical formula for the atomic inversion, which describes the effect of fluctuations. A closed equation is deduced for the field distribution function. In the markoff approximation such an equation reduces to the Fokker-Planck equation recently deduced by Mandel, which generalizes the Risken equation to the case of high-intensity lasers. The present method completely avoids the resummation of infinite terms of the kernel of the generalized master equation, performed by Mandel.