Dynamics of Strongly Coupled Modes between Surface Plasmon Polaritons and Photoactive Molecules: The Effect of the Stokes Shift

Abstract

We have investigated the dynamics of strongly coupled modes of surface plasmon polaritons (SPPs) and fluorescent molecules by analyzing their scattered emission polarization. While the scattered emission of SPPs is purely transverse magnetic (TM) polarized, the strong coupling with molecules induces transverse electric (TE) polarized emission via the partial molecular nature of the formed SPP–molecule polariton mode. We observe that the TM/TE ratio of the polariton emission follows the contribution of the molecular excited states in this hybrid mode. By using several types of molecules, we observe that, in addition to the coupling strength, which determines the contribution of the molecular excited states, also the Stokes shift of the molecule fluorescence influences the polarization of the emission: the larger the shift, the lower the TE-polarized emission. We argue that due to random orientation of the molecules, the emission of a fully coherent SPP–molecule polariton should be purely TM-polarized, like...