A two-level atom enclosed in a single-mode optical cavity is theoretically investigated in a parameter space in the steady state. The semiclassical and quantum behaviors of the system are discussed based on the different values of the critical photon number. The full quantum description has been compared once with the semiclassical approximation and once with the weak driving limit model. In the semiclassical approximation, the system behaves like a conventional laser, and in the weak driving limit, the antibunching quantum effects appear in the system. The performed simulations appropriately confirm the results of these two limit behaviors.
