Photon statistics of a dye laser far below threshold

The relative mean square fluctuations //sup 2/ of the intensity I of a single-mode dye laser have been measured by a photon counting technique, in the region from about threshold to intensities 1000 times below threshold. The results show a steady increase of //sup 2/ from less than 1 to about 150 as is reduced, followed by a rapid drop to zero. This behavior appears to be described fairly well by an equation of motion containing both additive spontaneous emission fluctuations and multiplicative pumping fluctuations.