LAUSR

Strongly coupled system is known to pose challenges, particularly those involving multitude of levels as in molecules. Surface plasmons offer intense and localized electromagnetic fields, wherein molecules placed in such environment exhibit generic features of strongly coupled system. We demonstrate the control over the splitting of surface plasmon polaritons dispersion branches in strong coupling regime within the absorption and fluorescence bands of Rhodamine-6G molecules placed on top of gold grating structures. The enhanced electromagnetic near-fields of surface plasmon polaritons excited on top of gold gratings have been calculated by numerical simulation and various aspects related to the coupling have been captured by modelling the Rhodamine-6G molecule as a theoretical three level Λ–system which support the experimentally observed variation in splitting with varying periods of gratings. The plasmonically enhanced electromagnetic field plays the role of a control field applied across one leg of the Λ–system. Experimentally measured spectral features, including level splitting and dispersions of the strongly coupled system of molecule-gold grating are consistently described by the model for a variety of samples, with different periodicities, different molecule-grating separations obtained through a dielectric spacer layer, and coupling to higher order diffraction modes of the grating.