Laser intensity fluctuations when the photon number at threshold is small

Previous calculations of laser threshold statistics have described the radiation field with a Fokker-Planck equation that embodies the approximation that the photon number at threshold is large. Here, the magnitude and correlation time of intensity fluctuations are calculated directly from the Scully-Lamb equation of motion for the reduced density matrix of a single-mode laser. This model does not embody a restriction to large photon number at threshold. We delineate the regime in which the threshold photon number is sufficiently small to produce measurable differences from the results of the usual Fokker-Planck analysis.