  The simplest model of a single-emitter laser generating in the regime of
small number of photons in the cavity is theoretically investigated. Based on a
system of equations for different moments of the field operators the analytical
expressions for mean number of photons and its dispersion are obtained. Using
the master equation approach the differential equation for the phase-averaged
quasi-probability Q is derived. For some limiting cases the exact solutions of
this equation are found.
