173 research outputs found
Coherent coupling of molecular resonators with a micro-cavity mode
The optical hybridization of the electronic states in strongly coupled
molecule-cavity systems have revealed unique properties such as lasing, room
temperature polariton condensation, and the modification of excited electronic
landscapes involved in molecular isomerization. Here we show that molecular
vibrational modes of the electronic ground state can also be coherently coupled
with a micro-cavity mode at room temperature, given the low vibrational thermal
occupation factors associated with molecular vibrations, and the collective
coupling of a large ensemble of molecules immersed within the cavity mode
volume. This enables the enhancement of the collective Rabi-exchange rate with
respect to the single oscillator coupling strength. The possibility of inducing
large shifts in the vibrational frequency of selected molecular bonds should
have immediate consequences for chemistry.Comment: 22 pages, 6 figures (including Supplementary Information file
Multiple Rabi Splittings under Ultra-Strong Vibrational Coupling
From the high vibrational dipolar strength offered by molecular liquids, we
demonstrate that a molecular vibration can be ultra-strongly coupled to
multiple IR cavity modes, with Rabi splittings reaching of the vibration
frequencies. As a proof of the ultra-strong coupling regime, our experimental
data unambiguously reveal the contributions to the polaritonic dynamics coming
from the anti-resonant terms in the interaction energy and from the dipolar
self-energy of the molecular vibrations themselves. In particular, we measure
the opening of a genuine vibrational polaritonic bandgap of ca. meV. We
also demonstrate that the multimode splitting effect defines a whole
vibrational ladder of heavy polaritonic states perfectly resolved. These
findings reveal the broad possibilities in the vibrational ultra-strong
coupling regime which impact both the optical and the molecular properties of
such coupled systems, in particular in the context of mode-selective chemistry.Comment: 10 pages, 9 figure
On columnar thin films as platforms for surface-plasmonic-polaritonic optical sensing: higher-order considerations
The ability to tailor the porosity and optical properties of columnar thin
films (CTFs) renders them promising platforms for optical sensing. In
particular, surface-plasmon-polariton (SPP) waves, guided by the planar
interface of an infiltrated CTF and a thin layer of metal, may be harnessed to
detect substances that penetrate the void regions in between the columns of a
CTF. This scenario was investigated theoretically using a higher-order
homogenization technique, based on an extended version of the second-order
strong-permittivity-fluctuation theory, which takes into account the size of
the component particles which make up the infiltrated CTF and the statistical
distribution of these particles. Our numerical studies revealed that as the
size of the component particles increases and as the correlation length that
characterizes their distribution increases: (i) the phase speed of the SPP wave
decreases and the SPP wave's attenuation increases; (ii) the SPP wave's
penetration into the CTF decreases; (iii) the angle of incidence required to
excite the SPP wave in a modified Kretschmann configuration increases; (iv) the
sharpness of the SPP trough in the graph of reflectance versus angle of
incidence increases; and (v) the sensitivity to changes in refractive index of
the infiltrating fluid decreases
Plasmon-Waveguide Resonances with Enhanced Figure of Merit and Their Potential for Anisotropic Biosensing in the Near Infrared Region
Modeling columnar thin films as platforms for surface-plasmonic-polaritonic optical sensing
Via exploitation of surface plasmon polaritons (SPPs), columnar thin films
(CTFs) are attractive potential platforms for optical sensing as their relative
permittivity dyadic and porosity can be tailored to order. Nanoscale model
parameters of a CTF were determined from its measured relative permittivity
dyadic, after inverting the Bruggeman homogenization formalism. These model
parameters were then used to determine the relative permittivity dyadic of a
fluid-infiltrated CTF. Two boundary-value problems were next solved: the first
relating to SPP-wave propagation guided by the planar interface of a
semi-infinitely thick metal and a semi-infinitely thick CTF, and the second to
the plane-wave response of the planar interface of a finitely thick metallic
layer and a CTF in a modified Kretschmann configuration. Numerical studies
revealed that SPP waves propagate at a lower phase speed and with a shorter
propagation length, if the fluid has a larger refractive index. Furthermore,
the angle of incidence required to excite an SPP wave in a modified Kretschmann
configuration increases as the refractive index of the fluid increases
Tilting a ground-state reactivity landscape by vibrational strong coupling
Many chemical methods have been developed to favor a particular product in transformations of compounds that have two or more reactive sites. We explored a different approach to site selectivity using vibrational strong coupling (VSC) between a reactant and the vacuum field of a microfluidic optical cavity. Specifically, we studied the reactivity of a compound bearing two possible silyl bond cleavage sites—Si–C and Si–O, respectively—as a function of VSC of three distinct vibrational modes in the dark. The results show that VSC can indeed tilt the reactivity landscape to favor one product over the other. Thermodynamic parameters reveal the presence of a large activation barrier and substantial changes to the activation entropy, confirming the modified chemical landscape under strong coupling
Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities
Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic semiconductors are of current interest for their room-temperature polariton formation. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polariton physics. Here we demonstrate polariton population from the triplet manifold via triplet-triplet annihilation, leading to polariton emission that is longer-lived (>microseconds) even than exciton emission in bare films. This enhancement arises from spin-2 triplet-pair states, formed by singlet fission or triplet-triplet annihilation, feeding the polariton. This is possible due to state mixing, which -in the strong coupling regime- leads to sharing of photonic character with states that are formally non-emissive. Such 'photonic sharing' offers the enticing possibility of harvesting or manipulating even states that are formally dark
Prism dispersion effects in near-guided-wave surface plasmon resonance sensors
Refractive index dispersion causes the light line to curve. As a result it is shown that when the prism is dispersive, an additional dip in the spectral response of Surface Plasmon Resonance (SPR) sensors is observed in the Kretschmann-Raether (KR) configuration. Since the new dip evolves in the infrared (IR) region, it exhibits a high sensitivity to the analyte refractive index (RI) changes and the mode penetrates deeper into the analyte. Adding a thin dielectric layer with high refractive index on top of the metallic layer enables to control the dip location and strength. The two dips shift in opposite directions as the analyte RI changes and therefore when the spectral difference is considered as the measurand, higher RI sensitivity is obtained. The dispersion relation of two thin films bounded by two semi-infinite media is derived when the prism dispersion is considered
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