Cooperative effects in a physically adsorbed monolayer of two-level atoms

We discuss the possibility of optical instability in a monolayer of two-level atoms physically adsorbed on a flat metallic surface. Taking into account the feedback mechanism and the local field correction we find the necessary and the sufficient conditions for the onset of bistability and we also obtain the resonance fluorescence spectrum and the rate of absorption from a probe field by an atom of the monolayer. Finally, we give a possible explanation in terms of cooperative interaction for the large decay rate found experimentally monolayers of low excited physically adsorbed atoms. (author). 19 refs