Abstract
We demonstrate optically induced crossover from a weak to a strong coupling regime in a single photonic system consisting of propagating surface plasmon polaritons (SPPs) on a planar silver film and ultraviolet (UV)-switchable photochromic molecules. A gradual increase is observed in the vacuum Rabi splitting upon increasing UV exposure, along with intriguing behavior, where the reflectivity initially decreases due to increased losses at the weak coupling regime, and then increases due to the emergence of strongly coupled modes and the associated band gap formation at the resonance frequency of the uncoupled states. This work explicitly demonstrates the optical tunability of the degree of hybridization of the SPP and exciton modes, spanning the range from weak to intermediate and finally to the strong coupling regime.
Highlights
Control over light-matter interactions forms the basis for many modern-day technologies [1,2]
One of the requirements to observe strong coupling is that the oscillators (SPPs and dye molecules) should have sufficiently narrow linewidths compared to the strength of the coupling [6]
The mode dispersions were calculated as E = hc/λ and kSPP = n · sin (α) · 2π/λ, where n is the refractive index of the substrate
Summary
Control over light-matter interactions forms the basis for many modern-day technologies [1,2]. The field of plasmonics focuses on optical modes, where the collective motion of charge carriers in a metal or a highly doped semiconductor is driven with light. These modes can be found in subwavelength structures that allow confining and manipulating light down to nm mode volumes [3]. Field confinement in plasmonic structures has enabled the observation of the interactions between dye molecules and optical fields in the weak, strong, [6] and even ultrastrong [7,8] coupling regimes. The advantage of using organic dyes in strong coupling is their small size, providing numerous oscillators in the small mode volume of the SPP modes (the coupling strength scales with the square root of the number of molecules [6])
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