Chasing Vibro-Polariton Fingerprints in Infrared and Raman Spectra Using Surface Lattice Resonances on Extended Metasurfaces

We present an experimental
investigation of vibrational strong
coupling of CO bonds in poly­(methyl methacrylate) to surface
lattice resonances (SLRs) on arrays of gold particles in infrared
and Raman spectra. SLRs are generated from the enhanced radiative
coupling of localized resonances in single particles by diffraction
in the array. Compared to previous studies in Fabry–Perot cavities,
particle arrays provide a fully open system that easily couples with
external radiation while having large field confinement close to the
array. We control the coupling by tuning the period of the array,
as evidenced by the splitting of the CO vibration resonance
in the lower and upper vibro-polaritons of the IR extinction spectra.
Despite clear evidence of vibrational strong coupling in IR transmission
spectra, both Raman spectroscopy and micro-Raman mapping do not show
any polariton signatures. Our results suggest that the search for
vibrational strong coupling in Raman spectra may need alternative
cavity designs or a different experimental approach.