We have shown that the Fano interference in the decay channels of a three-level system can lead to considerably different absorption and emission profiles. We found that a coherence can be built up in the ground state doublet, with strength depending on a coupling parameter that arises from the Fano interference. The coherence can in principle lead to breaking of the detail balance between the absorption and emission processes in atomic systems.
Quantum coherence and interference effects in atomic and molecular physics have been extensively studied because of intriguing counterintuitive physics and potential important applications. Here we present one such application, i.e. using quantum coherence to generate and enhance gain in the extreme ultra-violet (XUV)(@58.4nm in Helium) and infra-red (@794.76nm in Rubidium) regimes of electromagnetic radiation. We show that using moderate external coherent drive, a substantial enhancement in the output energy on the lasing transition can be achieved under optimal conditions. We also discuss the role of coherence. The present paper is intended to be pedagogical on this subject of coherence-enhanced lasing.
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