Enhancement of four-wave mixing due to coherent hole burning in a degenerate two-level system

Abstract We present a theoretical study of four-wave mixing (FWM) in a degenerate two-level atomic system subject to a magnetic field whose Zeeman sublevels constitute a tripod-type atomic system, which is driven by a linearly polarized field, and coupled and probed by two sets of left and right circularly polarized fields. The optical effects of coherent hole burning (CHB) and electromagnetically induced transparency (EIT) are involved in the coherent system, among which the CHB has much larger response for the FWM than the EITs. Three situations of CHB are involved, and they are the solitary CHB, overlapped CHBs, and an overlap between CHB and EIT. The overlapped CHBs have the greatest magnitude of FWM signal among the three situations. Whereas, for the overlapped CHB and EIT, it has the smallest FWM magnitude, which is no more than one tenth of the former. While for the single CHB, the FWM magnitude is half of that of the overlapped CHBs. It is noted that, in the overlap between CHB and EIT, dual EIAs can be obtained, whose FWM signal also has an enhancement in comparison to no EIA.