Interplay between strong coupling and radiative damping of excitons and surface plasmon polaritons in hybrid nanostructures.

We report on the interplay between strong coupling and radiative damping of strongly coupled excitons (Xs) and surface plasmon polaritons (SPPs) in a hybrid system made of J-aggregates and metal nanostructures. The optical response of the system is probed at the field level by angle-resolved spectral interferometry. We show that two different energy transfer channels coexist: coherent resonant dipole-dipole interaction and an incoherent exchange due to the spontaneous emissions of a photon by one emitter and its subsequent reabsorption by another. The interplay between both pathways results in a pronounced modification of the radiative damping due to the formation of super- and subradiant polariton states. This is confirmed by probing the ultrafast nonlinear response of the polariton system and explained within a coupled oscillator model. Such a strong modification of the radiative damping opens up interesting directions in coherent active plasmonics.