Spontaneous emission and level shifts in absorbing disordered dielectrics and dense atomic gases: A Green's-function approach

Spontaneous emission and Lamb shift of atoms in absorbing dielectrics and d ense atomic gases are discussed using a microscopic Green's-function approa ch. Uncorrelated and random atomic positions are assumed, and the associate d unphysical interactions between different atoms at the same location are eliminated (local field correction). For the case of an atom in a purely di spersive medium, the spontaneous-emission rate is altered by the well-known Lorentz local-field factor. When the mean distance between atoms becomes l ess than the resonance wavelength, results different from previously sugges ted expressions are found. In particular, it is shown that nearest-neighbor interactions become important. The results suggest that, for large densiti es, absorbing disordered dielectrics cannot accurately be described by a ma croscopic approach that neglects correlations between atomic positions. [S1 050-2947(99)08309-2].