Strong coupling of surface plasmon polaritons and ensembles of dye molecules

We demonstrate the strong coupling of dye molecules to surface plasmon polaritons (SPPs) excited in the Kretschmann geometry and propagating at the interface of silver and dye-doped polymer. The dispersion curve of such a system, studied in the reflectometry experiments, is split into three branches and demonstrates an avoided crossing - the signature of a strong coupling. We have further studied the excitation spectra of the dye emission and found that the positions of the excitation peaks have a good match with the points in the dispersion curve determined by the reflectometry. At the same time, the analysis of the spectra of the plasmon-mediated spontaneous emission, decoupled to the prism and acquired at multiple collection angles, has resulted in a quite different dispersion curve exhibiting a non-trivial splitting into multiple branches. This suggests that the same plasmonic environment couples differently to absorbing and emitting dye molecules.