Resonant Rayleigh Scattering from Collective Molecular Excitations

Resonant Rayleigh scattering (RRS) is the pronounced elastic scattering of photons present at the vicinity of the natural resonances of sub-wavelength physical objects such as molecules, which otherwise scatter negligibly. Here, we study RRS from molecular ensembles strongly coupled to an optical microcavity. Under these conditions, the coherent interaction between the molecules and the cavity mode produces collective molecular states known as cavity polaritons and which can drastically modify the properties these molecules. Our spectroscopic measurements reveal that strong RRS occurs at the polaritonic energies, reaching ~25% efficiency. Interestingly, this resonant scattering corresponds to the collective scattering of each photon from a macroscopically-large ensemble of molecules, rather than the scattering by individual ones, as in the usual case. We show that the scattering from the polaritonic states exhibit non trivial behaviors, specifically a linear dependence of the scattering strength on their photonic component. We believe that these observations, together with further investigation, may lead to a deeper understanding of these delocalized, collective molecular excitations, their non-equilibrium transport and the role of disorder in their dynamics.