Ultrafast Manipulation of Strong Coupling in Metal−Molecular Aggregate Hybrid Nanostructures

Abstract

We demonstrate an ultrafast manipulation of the Rabi splitting energy Ω(R) in a metal-molecular aggregate hybrid nanostructure. Femtosecond excitation drastically alters the optical properties of a model system formed by coating a gold nanoslit array with a thin J-aggregated dye layer. Controlled and reversible transient switching from strong (Ω(R) ≃ 55 meV) to weak (Ω(R) ≈ 0) coupling on a sub-ps time scale is directly evidenced by mapping the nonequilibrium dispersion relations of the coupled excitations. Such a strong, externally controllable coupling of excitons and surface plasmon polaritons is of considerable interest for ultrafast all-optical switching applications in nanoscale plasmonic circuits.

Strong coupling between surface plasmon polaritons and emitters: a review

“…The primary method of probing the dynamics of many photo-physical systems is that of pump-probe spectroscopy (see for example [156]). Vasa et al used pump-probe spectroscopy to investigate samples comprising J-aggregate layers deposited onto gold gratings [150]. They first showed that strong coupling was present in such systems, an anti-crossing appearing on their dispersion diagram, a diagram produced using experimentally determined reflectivity data, anti-crossing appearing where the grating-scattered SPP mode crossed the exciton absorption.…”

Absence of mutual polariton scattering for strongly coupled surface plasmon polaritons and dye molecules with a large Stokes shift

“…Despite these clear and consistent observations, the relaxation dynamics of the polaritons into the noncoupled MEs, as well as scatterings among them, are still not fully understood. 25,31,32 Recent time-resolved studies have shed some light on the issue, 33,34 and have demonstrated Rabi oscillations as a clear signature of strong coupling. 35 However, at the same time there has been significant evidence about unexpectedly long lifetimes of the polaritons, 36 suggesting more pronounced scattering or maybe even thermalization among them.…”

Real-time observation of ultrafast Rabi oscillations between excitons and plasmons in metal/molecular aggregate hybrid nanostructures

“…1b. Spectra reveal significant bending of the SPP and exciton resonances due to the formation of the upper (UP) and lower (LP) SPP-exciton polaritons, [2,5] with normal mode splitting, Ω NMS~1 10 meV. This strong normal mode splitting reflects the coupling of J-aggregate excitons localized near the nanoslits to the locally enhanced evanescent near field of the SPP.…”

“…1a using sub-15 fs pulses, sufficient to temporally resolve coherent exciton-SPP wavepacket dynamics. Figure 2 shows representative data displaying differential reflectivity spectra To analyze these results and to uncover the underlying physics, we have performed extensive density matrix simulations of the coupled system considering the molecular aggregate as a three level system exhibiting an exciton-biexciton transition while the SPP mode is modeled as a photonlike oscillator [2,3]. Essentially, the following scenario emerges.…”

“…In appropriately designed hybrids, the radiative coupling between the exciton dipole moment and local surface plasmon polariton (SPP) field can be so large that it greatly exceeds the linewidth of the uncoupled exciton and SPP resonances. In favorable cases, Rabi splittings of up to 700 meV have been observed, almost as large as the bandgap of the semiconductor and hence approaching the socalled ultrastrong coupling regime [1][2][3]. This unique combination of SPP-like propagation, excitonic optical nonlinearities and ultrastrong radiative coupling means that such hybrid nanostructures form a new class of functional materials offering novel possibilities to efficiently localize, switch and [4].…”