Molecular fluorescence at a rough surface: The orientation effects

The problem of the dynamical interaction between an emitting dipole and a metallic grating surface is considered with particular interest in the effects due to different orientations of the dipole with respect to the substrate surface. Our previous perturbative theory is extended to treat both parallel and perpendicular dipoles and the results are applied to the study of modified fluorescence characteristics for admolecules in the vicinity of a rough metal surface modeled as a grating. Numerical results show that some of the characteristics are very sensitive to the molecular orientation and the one along the grating direction is manifested with some unique behavior. The possibility of lengthening molecular lifetimes at a patterned surface is indicated via the manipulation of the surface roughness as well as the orientations of the molecules. In addition, the limitation of the usual step in averaging the theoretical results in the comparison with experimental measured values is pointed out.