Strong coupling regime is reached when SPPs and matter exchange energy coherently and reversibly before losses take place, resulting in the formation of new hybrid exciton-plasmon states formed by lower and upper energy bands [1,2]. In this field most of the works focus on steady-state observations, indeed experiments on the dynamics of such hybrid systems are relatively scarce and their intrinsic photophysics is still far from being understood.
Here, in order to improve our understanding of the dynamics of hybrid exciton-plasmon states, we have studied through ultrafast pump-probe approach, a hybrid system composed by gold hole arrays and J-aggregate molecules while modifying the lattice constant of the metallic array. Under upper hybrid band resonant excitation, transient absorption spectra provide the evidence that exciton-plasmon hybrid states are formed. Meanwhile, kinetics analysis led to the discovery of a remarkably long-lived upper band, at least one order of magnitude at 1/e than bare J-aggregate molecules. This result was explained with the identification, in the transient absorption spectra, of a trap state combined with the negligible relaxation effect from vibrational modes.
The intrinsic long lifetime of hybrid states is of crucial importance both from a fundamental and applicative point of view, having implications in the use of exciton-plasmon states for technological purposes. The understanding of the dynamics on strong coupling systems can provide indeed a promising route towards novel ultrafast plasmonic devices with coherent functionalities.
Hai Wang, Andrea Toma, Haiyu Wang, Hong-Bo Sun, and Remo Proietti Zaccaria, "Dynamics between J-aggregates and surface plasmon polaritons in strong coupling regime
(Conference Presentation)," Proc. SPIE 9925, Nanoimaging and Nanospectroscopy IV, 99250B (Presented at SPIE Nanoscience + Engineering: August 28, 2016; Published: 11 November 2016); https://doi.org/10.1117/12.2240072.5161498087001.
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