Evolution of spontaneous emission of a laser active medium in a resonator of an unstable geometric configuration

The process of propagation of a beam of spontaneous emission inside the unstable resonator is considered. Spontaneous emission of the active element is taken as the sum of spatial-deltacorrelated fields from a set of point sources. The dependence of the correlation function of the output laser radiation from the number of intracavity passes explored. A relation to estimate the number of passes required to form a resonant field is derived.