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Theory of strong coupling between molecules and surface plasmons on a grating.

Published version
Peer-reviewed

Type

Article

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Authors

Arul, Rakesh 
Baumberg, Jeremy J 
Barnes, William L 

Abstract

The strong coupling of molecules with surface plasmons results in hybrid states which are part molecule, part surface-bound light. Since molecular resonances may acquire the spatial coherence of plasmons, which have mm-scale propagation lengths, strong-coupling with molecular resonances potentially enables long-range molecular energy transfer. Gratings are often used to couple incident light to surface plasmons, by scattering the otherwise non-radiative surface plasmon inside the light-line. We calculate the dispersion relation for surface plasmons strongly coupled to molecular resonances when grating scattering is involved. By treating the molecules as independent oscillators rather than the more typically considered single collective dipole, we find the full multi-band dispersion relation. This approach offers a natural way to include the dark states in the dispersion. We demonstrate that for a molecular resonance tuned near the crossing point of forward and backward grating-scattered plasmon modes, the interaction between plasmons and molecules gives a five-band dispersion relation, including a bright state not captured in calculations using a single collective dipole. We also show that the role of the grating in breaking the translational invariance of the system appears in the position-dependent coupling between the molecules and the surface plasmon. The presence of the grating is thus not only important for the experimental observation of molecule-surface-plasmon coupling, but also provides an additional design parameter that tunes the system.

Description

Keywords

gratings, molecule–light interactions, strong coupling, surface plasmons

Journal Title

Nanophotonics

Conference Name

Journal ISSN

2192-8606
2192-8614

Volume Title

11

Publisher

Walter de Gruyter GmbH
Sponsorship
Engineering and Physical Sciences Research Council (EP/L027151/1)
Engineering and Physical Sciences Research Council (EP/L015978/1)
Engineering and Physical Sciences Research Council (EP/P029426/1)
Engineering and Physical Sciences Research Council (EP/R020965/1)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (829067)
Engineering and Physical Sciences Research Council (EP/S022953/1)
European Commission Horizon 2020 (H2020) Research Infrastructures (RI) (861950)
European Commission Horizon 2020 (H2020) ERC (883703)