Quantum-jump analysis of frequency up-conversion amplification without inversion in a four-level scheme

In this work, we use the quantum-jump approach to study light-matter interactions in a four-level scheme giving rise to frequency up-conversion amplification without inversion (AWI). The results obtained apply to the case of neutral Hg vapor where the AWI of a probe field in the UV regime was recently reported, opening the way for lasing without inversion in this range of frequencies. We show that, in this scheme, the key element to obtain maximum amplification is the fulfillment of the three-photon resonance condition, which favors coherent evolution periods associated with the probe field gain. We also investigate the parameter values to optimize amplification. The present study extends the theoretical understanding of the underlying mechanisms involved in AWI.