Multimode Coherent Hybrid States: Ultrafast Investigation of Double Rabi Splitting between Surface Plasmons and Sulforhodamine 101 Dyes

A multimode coherent hybrid system formed by strongly coupled surface plasmons in gold nanohole arrays and excitons in sulforhodamine 101 dyes is investigated by using both a steady‐state spectroscopic method and a femtosecond transient absorption spectra approach. A double Rabi splitting up to 255 meV and 188 meV is observed in steady‐state transmission measurements. Furthermore, the dynamics of the multimode coherent hybrid system are studied under upper band resonant excitation. It is found that the bleaching signal associated with uncoupled sulforhodamine 101 molecules completely disappears. Instead, two distinctive bleaching signals corresponding to the middle and lower bands are formed, thus highlighting the presence of coherent hybrid states. Finally, a remarkebly long lifetime for the lower band is observed, even longer than the bleaching recovery of the uncoupled dyes, in perfect agreement with the non‐Markovian regime. These peculiar features can provide new perspectives for coherent energy transfer and mode‐selective chemistry, thus enriching the tools available in the chemical reaction landscape.