ph7b00583_si_001.pdf (1.17 MB)
Vibrational Strong Coupling Controlled by Spatial Distribution of Molecules within the Optical Cavity
journal contribution
posted on 2017-09-29, 00:00 authored by Wonmi Ahn, Igor Vurgaftman, Adam D. Dunkelberger, Jeffrey C. Owrutsky, Blake S. SimpkinsSimilar to excitonic
materials interacting with optical cavity
fields, vibrational absorbers coupled to resonantly matched optical
modes can exhibit new hybridized energy states called cavity polaritons.
The delocalized nature of these hybrid polaritonic states can potentially
modify a material’s physical and chemical characteristics,
with the promise of a significant impact on reaction chemistry. In
this study, we investigate the relationship between the spatial distribution
of vibrational absorbers and the cavity mode profile in vibrational
strong coupling by systematically varying the location of a 245-nm-thick
poly(methyl methacrylate) (PMMA) film within a few-micrometer-thick
Fabry–Perot cavity. Angle-tuning the cavity reveals that the
first- and second-order cavity resonances couple to molecular absorption
lines of PMMA (the CO and C–H stretching bands at 1731
and 2952 cm–1, respectively), resulting in quantifiable
vacuum Rabi splittings in the dispersion response. These splittings,
as extracted from experiment, transfer-matrix calculations, and an
analytical treatment, display a consistent and strong dependence on
the molecular spatial distribution within a cavity. Furthermore, we
demonstrate the response of two physically separated molecular layers
by measuring and calculating the vacuum Rabi splitting for cavities
loaded with single and widely spaced pairs of PMMA layers. The results
provide evidence that extended cavity polariton modes sample these
separate layers simultaneously and, more broadly, provide guidance
for controlling the coupling strength, and potentially chemical reactivity,
of a given region through modification of the cavity mode profile
or through introducing a remotely located molecular layer.