Perturbative solution to the single-mode model of superradiance
Lorenzo M. Narducci, V. Bluemel · Physical Review A · 1975
We use a perturbative approach to analyze the diffusion equation for the atomic quasiprobability function derived by Narducci, Coulter, and Bowden, and demonstrate explicitly that the first-order correction contributes to the atomic moments only to order $\frac{1}{N}$, where $N$ is proportional to the cooperation number.