Exciton–surface plasmon interactions

A thin film possessing excitonic states within the range of energies of a plasmon surface polariton of a metallic substrate can strongly influence this surface electromagnetic wave either by a resonance interaction or a quenching interaction. We have analyzed this coupling and present our results showing the effects of an anisotropic orientation in the molecular film compared to an isotropic orientation and the effects of damping of the molecular electronic transition in the film. In a typical attenuated total reflection (ATR) experiment either an angular scan or a wavelength scan is usually used. A comparison of these two situations is given and sample calculations are displayed with perspective figures of reflectivity versus both angle and wavelength. The results show that a combination of both types of scans, i.e., angular scans at a series of wavelengths or wavelength scans at a series of angles or some combination to follow along the dispersion curve, are necessary to map the dispersion. Further isotropic excitons interact with the plasmon surface polariton at two wavelengths and anisotropic excitons interact at either one or the other depending on the orientation.