Laser linewidth and operator orderings

Abstract

We demonstrate explicitly that, after including the saturation effects of a laser diffusion coefficients,(i) the phase diffusion coefficients given by the normal-ordering P and the antinormal-ordering Q functions become equal, implying that the laser linewidth is independent of the operator orderings of different quasiprobability functions; and (ii) the intensity diffusion coefficients given by the two functions are still different, but leading to the same photon-number variance.