Inversionless amplification in three-level systems: dressed states quantum interference and quantum-jump analyses

We investigate amplification without inversion (AWI) in different three-level systems driven by an on-resonance coherent field and identify the elements that contribute to destructive or constructive dressed states quantum interference in the probe field absorption spectrum. We determine analytically the conditions for \{AWI\} at the probe field line center and at the wings of the resonance region. For this latter case, we explicitly locate the position of the maximum gain as a function of the probe field detuning. Finally, through a quantum-jump analysis, we find that \{AWI\} at the wings of the resonance region is due to an asymmetry between one-photon-stimulated emission and absorption processes, in contrast with \{AWI\} at the line center which arises from the contribution of two-photon gain.