Inversionless amplification and propagation in an electronuclear level-mixing scheme

We study the propagation of a drive and probe bichromatic field in a compound electronuclear system [Opt. Commun. 179, 525 (2000)] from the viewpoint of inversionless amplification. In the regimes of adiabatic pulse and steady-state propagation, part of the ground-state population is trapped in a dark state thereby reducing the absorption of a probe field. This is reinforced by spontaneous emission for the steady-state case, for which the optimal amplification length is calculated. Beyond this length, the medium becomes absorbent for the probe field. In the complementary limit of ultrashort pulses, the medium reduces to a V scheme in which the drive field can self-induce transparency.