The gain amplification via spontaneously generated coherence with incoherent pump field: A comparison of optical properties between open and closed four level systems

We studied the steady state and transient evolution of probe absorption and population in an open four level N-type atomic system and compared its transient and steady state properties with the corresponding closed system. The effects of incoherent pump field, spontaneously generated coherence, probe detuning and cavity parameters (i.e. the atomic exit rate from cavity and atomic injection rates) on transient and steady state response of probe field and lasing with and without inversion are investigated. It is realized that in an open N-type system, regardless of incoherent pump field applied or not, due to existence of cavity parameter, by adjusting the values of other parameters, we can always obtain lasing without inversion, while there is no gain in closed system without incoherent pump field. Also results are shown that, the probe gain can be greatly amplified with SGC at the presence of incoherent pump field and absence of population inversion. We found that in the same condition the open system is favorable scheme for lasing without inversion.