A system consisting of a three-level atom trapped in a single-mode optical cavity is theoretically investigated. Under different conditions, this system can illustrate the behaviors of a semi-classical laser or quantum treatments. The descriptive master equation of this system is solved numerically in the atom and cavity basis. The results show that near the semi-classical approximation for when a large number of photons are present in the cavity, the system described by the semi-classical laser theory and for when a small number of photons exist in the cavity and in the weak driving limit, the emitted light by the system is antibunching which is a quantum effect.
