Search for: All records

Abstract Nanostructured plasmonic surfaces allow for precise tailoring of electromagnetic modes within sub-diffraction mode volumes, boosting light–matter interactions. This study explores vibrational strong coupling (VSC) between molecular ensembles and subradiant “dark” cavities that support infrared quadrupolar plasmonic resonances (QPLs). The QPL mode exhibits a dispersion characteristic of bound states in the continuum (BIC). That is, the mode is subradiant or evanescent at normal incidence and acquires increasing “bright” dipole character with larger in-plane wavevectors. We deposited polymethyl methacrylate (PMMA) thin films on QPL substrates to induce VSC with the carbonyl stretch in PMMA and measured the resulting infrared (IR) spectra. Our computational analysis predicts the presence of “dark” subradiant polariton states within the near-field of the QPL mode, and “bright” collective molecular states. This finding is consistent with classical and quantum mechanical descriptions of VSC that predict hybrid polariton states with cavity-like modal character andN−1collective molecular states with minimal cavity character. However, the behaviour is opposite of what is standardly observed in VSC experiments that use “bright” cavities, which results in “bright” polariton states that can be spectrally resolved as well asN−1collective molecular states that are spectrally absent. Our experiments confirm a reduction of molecular absorption and other spectral signatures of VSC with the QPL mode. In comparison, our experiments promoting VSC with dipolar plasmonic resonances (DPLs) reproduce the conventional behavior. Our results highlight the significance of cavity mode symmetry in modifying the properties of the resultant states from VSC, while offering prospects for direct experimental probing of theN−1molecule-like states that are usually spectrally “dark”. 

Localized surface plasmon resonances (LSPRs) in metallic nanostructures result in subwavelength optical confinement that enhances light–matter interactions, for example, aiding the sensitivity of surface spectroscopies. The dissipation of surface plasmons as electronic and vibrational excitations sets the limit for field confinement but also provides opportunities for photochemistry, photocatalysis, and photothermal heating. Optimization for either goal requires a deeper understanding of this photothermalization process. In this review, we focus on recent insights into the physics and dynamics governing photothermalization of LSPRs in metallic nanostructures, emphasizing comparisons between the steady-state behavior and ultrafast time-resolved studies. The differences between these regimes inform how to best optimize plasmonic systems for applications under relatively low-intensity, continuous illumination (e.g., sunlight).