Collective emission of atoms in photonic bandgap materials

A system of resonance atoms doped into a photonic bandgap material is considered in the case when the resonance transition frequency lies within the band gap. Spontaneous emission of a single atom is suppressed in this situation, which is called the light localisation. It is shown that, if the density of the doped atoms is sufficiently high, the coherent interaction between atoms can appear, resulting in the emission of a single or a series of coherent pulses by a system of atoms.