57 research outputs found
How nonlocal damping reduces plasmon-enhanced fluorescence in ultranarrow gaps
The nonclassical modification of plasmon-assisted fluorescence enhancement is
theoretically explored by placing two-level dipole emitters at the narrow gaps
encountered in canonical plasmonic architectures, namely dimers and trimers of
different metallic nanoparticles. Through detailed simulations, in comparison
with appropriate analytical modelling, it is shown that within classical
electrodynamics, and for the reduced separations explored here, fluorescence
enhancement factors of the order of can be achieved, with a divergent
behaviour as the particle touching regime is approached. This remarkable
prediction is mainly governed by the dramatic increase in excitation rate
triggered by the corresponding field enhancement inside the gaps. Nevertheless,
once nonclassical corrections are included, the amplification factors decrease
by up to two orders of magnitude and a saturation regime for narrower gaps is
reached. These nonclassical limitations are demonstrated by simulations based
on the generalised nonlocal optical response theory, which accounts in an
efficient way not only for nonlocal screening, but also for the enhanced Landau
damping near the metal surface. A simple strategy to introduce nonlocal
corrections to the analytic solutions is also proposed. It is therefore shown
that the nonlocal optical response of the metal imposes more realistic, finite
upper bounds to the enhancement feasible with ultrasmall plasmonic cavities,
thus providing a theoretical description closer to state of the art
experiments
Robustness of the Rabi splitting under nonlocal corrections in plexcitonics
We explore theoretically how nonlocal corrections in the description of the
metal affect the strong coupling between excitons and plasmons in typical
examples where nonlocal effects are anticipated to be strong, namely small
metallic nanoparticles, thin metallic nanoshells or dimers with narrow
separations, either coated with or encapsulating an excitonic layer. Through
detailed simulations based on the generalised nonlocal optical response theory,
which simultaneously accounts both for modal shifts due to screening and for
surface-enhanced Landau damping, we show that, contrary to expectations, the
influence of nonlocality is rather limited, as in most occasions the width of
the Rabi splitting remains largely unaffected and the two hybrid modes are well
distinguishable. We discuss how this behaviour can be understood in view of the
popular coupled-harmonic-oscillator model, while we also provide analytic
solutions based on Mie theory to describe the hybrid modes in the case of
matryoshka-like single nanoparticles. Our analysis provides an answer to a so
far open question, that of the influence of nonlocality on strong coupling, and
is expected to facilitate the design and study of plexcitonic architectures
with ultrafine geometrical details
Enhanced ponderomotive force in graphene due to interband resonance
We analyze intrinsic nonlinearities in two-dimensional polaritonic materials
interacting with an optical wave. Focusing on the case of graphene, we show
that the second-order nonlinear optical conductivity due to carrier density
fluctuations associated with the excitation of a plasmon polariton is closely
related to the ponderomotive force due to the oscillating optical field. This
relation is first established through an elegant thermodynamic approach for a
Drude-like plasma, in the frequency range where intraband scattering is the
dominant contribution to conductivity. Subsequently, we extend our analysis to
the interband regime, and show that for energies approximately half the Fermi
energy, the intraband contribution to the ponderomotive force diverges. In
practice, thermal broadening regularizes this divergence as one would expect,
but even at room temperature typically leaves a strong ponderomotive
enhancement. Finally, we study the impact of nonlocal corrections and find that
nonlocality does not lead to further broadening (as one would expect in the
case of Landau damping), but rather to a splitting of the ponderomotive
interband resonance. Our analysis should prove useful to the open quest for
exploiting nonlinearities in graphene and other two-dimensional polaritonic
materials, through effects such as second harmonic generation and photon drag.Comment: 7 pages, 2 figures, 1 appendi
Nonlocal quasinormal modes for arbitrarily shaped three-dimensional plasmonic resonators
Nonlocal effects have been shown to be responsible for a variety of
non-trivial optical effects in small-size plasmonic nanoparticles, beyond
classical electrodynamics. However, it is not clear whether optical mode
descriptions can be applied to such extreme confinement regimes. Here, we
present a powerful and intuitive quasinormal mode description of the nonlocal
optical response for three-dimensional plasmonic nanoresonators. The nonlocal
hydrodynamical model and a generalized nonlocal optical response model for
plasmonic nanoresonators are used to construct an intuitive modal theory and to
compare to the local Drude model response theory. Using the example of a gold
nanorod, we show how an efficient quasinormal mode picture is able to
accurately capture the blueshift of the resonances, the higher damping rates in
plasmonic nanoresonators, and the modified spatial profile of the plasmon
quasinormal modes, even at the single mode level. We exemplify the use of this
theory by calculating the Purcell factors of single quantum emitters, the
electron energy-loss spectroscopy spatial maps, as well as the Mollow triplet
spectra of field-driven quantum dots with and without nonlocal effects for
different size nanoresonators. Our nonlocal quasinormal mode theory offers a
reliable and efficient technique to study both classical and quantum optical
problems in nanoplasmonics
Robustness of the far-field response of nonlocal plasmonic ensembles
Contrary to classical predictions, the optical response of few-nm plasmonic
particles depends on particle size due to effects such as nonlocality and
electron spill-out. Ensembles of such nanoparticles (NPs) are therefore
expected to exhibit a nonclassical inhomogeneous spectral broadening due to
size distribution. For a normal distribution of free-electron NPs, and within
the simple nonlocal Hydrodynamic Drude Model (HDM), both the nonlocal blueshift
and the plasmon linewidth are shown to be considerably affected by ensemble
averaging. Size-variance effects tend however to conceal nonlocality to a
lesser extent when the homogeneous size-dependent broadening of individual NPs
is taken into account, either through a local size-dependent damping (SDD)
model or through the Generalized Nonlocal Optical Response (GNOR) theory. The
role of ensemble averaging is further explored in realistic distributions of
noble-metal NPs, as encountered in experiments, while an analytical expression
to evaluate the importance of inhomogeneous broadening through measurable
quantities is developed. Our findings are independent of the specific
nonclassical theory used, thus providing important insight into a large range
of experiments on nanoscale and quantum plasmonics
Molecular fluorescence enhancement in plasmonic environments: exploring the role of nonlocal effects
Nonlocal effects in atom-plasmon interactions
Nonlocal and quantum mechanical phenomena in noble metal nanostructures
become increasingly crucial when the relevant length scales in hybrid
nanostructures reach the few-nanometer regime. In practice, such mesoscopic
effects at metal-dielectric interfaces can be described using exemplary
surface-response functions (SRFs) embodied by the Feibelman -parameters.
Here we show that SRFs dramatically influence quantum electrodynamic phenomena
-- such as the Purcell enhancement and Lamb shift -- for quantum emitters close
to a diverse range of noble metal nanostructures interfacing different
homogeneous media. Dielectric environments with higher permittivities are shown
to increase the magnitude of SRFs calculated within the specular-reflection
model. In parallel, the role of SRFs is enhanced in nanostructures
characterized by large surface-to-volume ratios, such as thin planar metallic
films or shells of core-shell nanoparticles. By investigating emitter quantum
dynamics close to such plasmonic architectures, we show that decreasing the
width of the metal region, or increasing the permittivity of the interfacing
dielectric, leads to a significant change in the Purcell enhancement, Lamb
shift, and visible far-field spontaneous emission spectrum, as an immediate
consequence of SRFs. We anticipate that fitting the theoretically modelled
spectra to experiments could allow for experimental determination of the
-parameters.Comment: 9 pages, 5 figure
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