Laser-noise suppression in the dressed-atom approach. I. Fluctuations in a regularly pumped laser

The dressed-atom approach to the fluctuation problem in lasers is described. Such an approach allows one to analyze the fluctuations in various kinds of laser models. The intensity fluctuations in a regularly pumped laser are considered in the framework of the dressed-atom approach. The Fokker-Plank equation for the field density matrix is derived from first principles without heuristic assumptions. An alternative interpretation of the noise suppression in the regularly pumped laser is given. It is based upon the nonstationary picture for atomic variables. In such a regime the statistics of the output laser field may be controlled by the input statistics of the atomic initial conditions. It is the regular pump that provides the best input statistics. In the latter case the atoms are essentially nonstationary and coherently oscillate at the Rabi frequency. They are treated in a framework of the time-dependent picture in spite of the short atomic lifetime as compared with the cavity mode lifetime. The nonstationary version of the dressed-atom approach is employed to treat the regular pump case. It is demonstrated that a coherent coupling of the Rabi oscillations in the quadratic dressed-atom terms gives rise to a survival of a linear inverse proportional dependence of the atomic correlation functions upon field intensity. This survival in turn accounts for the anomalously large dressed-atom contribution to the fluctuations. Our results are in quantitative agreement with those of other approaches.