Transparency and Strong Gain Without Population Inversion in Photonic Bandgap Crystals

Without using the weak-field approximation, we investigate the transient properties of a Λ-type atom with one transition near resonant with a photonic bandgap edge. Whatever the initial state of the atom is, the atom can become transparent to a probe field, and strong gain without population inversion is also possible if the atom has been pre-excited. The defect mode formed by atomic doping can have strong effect on the absorption properties of the atom.