The impact of decay-induced interference on transient behaviours of the dispersion and the absorption

The dynamical behaviour of the dispersion and the absorption in a nearly equispaced ladder-type three-level atomic system is investigated. It is shown that in the presence of decay-induced interference the probe dispersion and absorption are phase dependent. The required switching times for switching the group velocity of a probe field from subluminal to superluminal pulse propagation is then discussed. We find that applying an incoherent pumping field provides an additional control parameter for switching the probe absorption to probe gain.