Heisenberg approach for superradiant lasers and nonlinear open systems

Nonlinear operator equations for micro-lasers and resonant optical devices are solving beyond the rate equation approach, without adiabatic elimination of polarization. Frequency component operators are found, fluctuation power spectra and mean values are calculated. Various analytical approximations are discussed. Thresholdless lasing, radiation linewidth, collective Rabi splitting, super-thermal photon statistics and the radiation power increase by population fluctuations are discussed.