We have measured the photon number probability distribution of a laser in which the inversion is not slaved to the field. For the experiments, we have used a ${\mathrm{Nd}}^{3+}:{\mathrm{YVO}}_4$ laser which has a sufficiently slow inversion to allow measurement of the photon fluctuations at a time scale much shorter than that of the relaxation oscillations. The photon distribution function becomes highly nonstandard (i.e., non-Poissonian) in such a laser; this is consistent with available theoretical work. We point out the relevance of our results for the case of the semiconductor microlaser.

• Received 22 September 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.2786