Strong Plasmon–Exciton Coupling with Directional Absorption Features in Optically Thin Hybrid Nanohole Metasurfaces

Abstract

Plasmons and excitons can interact to form new hybridized light–matter states, with a multitude of potential applications including optical logic circuits and single-photon switches. Here, we report the first observation of strong coupling based on optically thin plasmonic nanohole films. The absorptive plasmon resonances of these nanohole films lead to suppressed transmission and Fano-shaped extinction peaks. We prepared silver nanohole films by colloidal lithography, which enables large-scale fabrication of nanoholes distributed in a short-range order. When coated with J-aggregate molecules, both extinction and absorption spectra show clear formation of two separated polariton resonances, with vacuum Rabi splitting on the order of 300 meV determined from anticrossing experiments. In accordance with strong coupling theory, the splitting magnitude increases linearly with the square root of molecular concentration. The extinction peak positions are blue-shifted from the absorption polariton positions, as explained by additional Fano interference between the hybridized states and the metal film. This highlights that absorption measurements are important not only to prove strong coupling but also to correctly determine hybridized polariton positions and splitting magnitudes in hybrid plasmonic nanohole systems. The polariton absorption peaks also show strong dependence on illumination direction, as found related to inherent directionality of the plasmonic nanohole metasurface and differences in light interaction with nonhybridized molecules. Importantly, optical simulations could successfully reproduce the experimental results and all coupling features. Furthermore, simulated spatial distribution of the absorption provides additional evidence of strong coupling in the hybrid nanohole system. The work paves the way toward strong coupling applications based on optically thin nanohole systems, as further promoted by the scalable fabrication.

Selective grating obtained by dye microstructuration based on local photobleaching using a laser writer

“…We have periodically insolated dye on silver showing many patterning possibilities for wavelength selective grating fabrication. This work thus highlights the high potential of the localphoto-bleaching method for obtaining many kind of micro-structured geometries in organic emitters, and could be applied for different applications like strong coupling studies [6,7,19,26] or wavelength selective grating [11][12][13][14][15]17].…”

“…A 50 nm thick silver layer was thermally evaporated on glass substrate, and an aqueous solution of J-aggregated dye TDBC (5,6-Dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulfobutyl)benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulfobutyl)benzimidazolium hydroxide, inner salt, sodium salt) is spin coated on top of the silver film (Figure 1-a). The concentration of the TDBC aqueous solution is 8.39×10 -3 M. This active molecule on silver has been chosen because it is widely used in strong coupling studies [7,18,19]. The spin coated layer has a 17 nm thickness measured by plasmon fitting [7].…”

Plasmonic fanoholes: on the gradual transition from suppressed to enhanced optical transmission through nanohole arrays in metal films of increasing film thickness

“…These results are consistent for both asymmetric nanohole films on a substrate and for symmetric freestanding nanohole films. In turn, this deviation between transmission extrema and resonances is important to consider when designing plasmonic nanohole systems for use in different applications, such as for biosensors [8,30,31], light-to-heat conversion [24], or for strongly coupled systems [47,53]. We suggest that measuring absorption peaks, for example, using an integrating sphere, form a suitable approach to identify plasmon resonances in plasmonic nanohole systems and similar systems where Fano interference effects may otherwise disguise the true resonances.…”

Light-emitting metasurfaces

“…An emerging field in plasmonics is collective strong coupling, where the concentration of emitters is taken as high as possible to boost the (collective) oscillator strength. Indeed, the signatures of strong coupling have been reported in systems that coupled organic dye excitons with SPP Bloch modes in nanohole arrays [277][278][279] and collective resonances of plasmonic nanoparticle arrays [79,280,281]. This is an exciting research direction for metal and dielectric metasurfaces, as the hybrid metasurface-exciton states can support effects such as condensation [282,283], concomitantly coherent emission [123,284], optical nonlinearity [285,286], and magneto-optical response [287] allowing, e.g.…”