Linear and quadratic behaviors in a two-level laser

A two-level atom is enclosed in a single-mode optical cavity, and the occurring processes in this system have been theoretically examined in the steady-state. In the non-resonance case and in several different instances, the lasing and non-lasing regimes are specified in the semiclassical approximation in the parameter space. The behavior of the system is fully described for the time when there are a small or large number of photons in the cavity. The semiclassical approximation is shown in two different frameworks, and its results are well confirmed by the quantum simulations when there are many photons in the cavity. To observe the change in the behavior of the emitted light near the laser threshold, the second order coherence function and the Fano factor have been used. In explaining the antibunching process, the explicit form of the second order coherence function has been obtained in two different representations. This function is equal in both representations to the lowest order and its findings are in good agreement with the quantum model.