Impact of Interacting Quantum Coherence via Decays and Incoherent Pumping on Transient and Steady-State Behaviors of Absorption

The effects from quantum coherence via decays and incoherent pumping on the lasing without inversion (LWI) are investigated in a four-level system. By analyzing the transient and steady-state behaviors of the absorption, we find that the gain occurs when both spontaneously generated coherence (SGC) and coherence induced by incoherent pumping (IPC) are considered. We attribute the occurrence of the gain to the interaction of quantum coherence via decays and incoherent pumping.