Transient properties of atomic coherence induced by an nonsingular-DOM reservoir

We investigate the transient properties of an open A-type atomic system with one transition coupled with a modified radiation reservoir. This system can be transparent or nearly transparent to a weak probe field. This open atomic system has no true steady state due to the background decay of the excited state, unless the probe field is tuned to be Raman-resonant to a high-Q defect mode, when the coherent population trapping occurs and lead to a steady state being insensitive to the singularity/smoothness feature of the density of modes (DOM) at band-gap edge. The transient gain without population inversion can occur for a nonsingular DOM as well as for a singular DOM and, in the presence of defect modes, the nonsingularity of the DOM at band edge can even enhance the gain. (C) 2004 Elsevier B.V. All rights reserved.