Local field effects in multicomponent media

We investigate local-field effects in nonlinear optical materials composed of two species of atoms. One species of atom is assumed to be near resonance with an applied field and is modeled as a two-level system while the other species of atom is assumed to be in the linear regime. If the near dipole-dipole interaction between two-level atoms is negligible, the usual local-field enhancement of the field is obtained. For the case in which near-dipole-dipole interactions are significant due to a high density of two-level atoms, local-field effects associated with the presence of a optically linear material component lead to local-field enhancement of the near dipole-dipole interaction, intrinsic cooperative decays, and coherence exchange processes. (C) 1997 Optical Society of America