On the dominant role of two-photon relaxation in photonic crystals in external fields

It is shown that resonant interaction of a coherent wave with impurity atom s leads to filling of levels of an impurity atom that lie in the gap in the photon density of states and do not belong to resonant transitions, while the interaction of impurity atoms with a nonresonant coherent wave results in effective deactivation of the indicated levels. The main mechanism deter mining the pumping and decay of an impurity level in a gap are two-photon r adiative relaxation processes previously investigated by the present author (Zh. Eksp. Teor. Fiz. 102, 1126 (1992) [Sov. Phys. JETP 75, 611 (1992)]). (C) 1999 American Institute of Physics. [S0021-3640(99)00419-3].