A study of optical properties of a four-level atomic system via vacuum-induced coherence effects

This paper studies the effects of vacuum-induced coherence (VIC) in a four-level atomic system. The effects of VIC lead to the coherent hole burnings exhibited in the system at some certain points of the Rabi frequency. This is also the reason for the enhancement of the coherent population trapping. In addition, optical bistability occurs in the evolution curves of absorption versus the phase of Rabi frequencies.