Ultrafast manipulation of the Rabi splitting in metal-molecular aggregate hybrid nanostructures

We report on an experimental study of the optical properties of a metal-molecular aggregate hybrid nanostructure consisting of a gold nanoslit array coated with a thin J-aggregated dye layer. Our experiments reveal a strong coupling between the surface plasmon polaritons (SPPs) excited on a nanoslit array and the aggregate excitons with a large Rabi splitting energy (ΩR). Ultrafast excitation drastically alters the optical response of the hybrid nanostructure inducing transient switching from the strong to weak the coupling regime due to the bleaching of the exciton resonance. The externally controlled switching is fully reversible and occurs on sub-ps timescale. The results are explained within a phenomenological two coupled oscillator model. Such a strong interaction can, e.g., be used to fabricate ultrafast all-optical plasmonic switches or tunable mirrors.