Atomic correlations in a laser

Regular perturbation theory is used to construct the theory of a single-mode laser based on two-level atoms with appropriate allowance for atomic correlations. As small parameters, the adiahaticity parameter (the ratio of the relaxation constants of the field and the atoms) and the ratio of the coupling constant to the atomic relaxation constant are chosen. A solution is obtained for the density matrix of the field in the stationary ease; this being a generalized function of the amplitude in the representation of coheren states.