583 research outputs found
Field expansions for systems of strongly coupled plasmonic nanoparticles
This paper is concerned with efficient representations and approximations of
the solution to the scattering problem by a system of strongly coupled
plasmonic particles. Three schemes are developed: the first is the resonant
expansion which uses the resonant modes of the system of particles computed by
a conformal transformation, the second is the hybridized resonant expansion
which uses linear combinations of the resonant modes for each of the particles
in the system as a basis to represent the solution, and the last one is the
multipole expansion with respect to the origin. By considering a system formed
by two plasmonic particles of circular shape, we demonstrate the relations
between these expansion schemes and their advantages and disadvantages both
analytically and numerically. In particular, we emphasize the efficiency of the
resonant expansion scheme in approximating the near field of the system of
particles. The difference between these plasmonic particle systems and the
nonresonant dielectric particle system is also highlighted. The paper provides
a guidance on the challenges for numerical simulations of strongly coupled
plasmonic systems.Comment: 16 pages, 1 figur
Level repulsion in hybrid photonic-plasmonic microresonators for enhanced biodetection
We theoretically analyse photonic-plasmonic coupling between a high Q
whispering gallery mode (WGM) resonator and a core-shell nanoparticle. Blue and
red shifts of WGM resonances are shown to arise from crossing of the photonic
and plasmonic modes. Level repulsion in the hybrid system is further seen to
enable sensitivity enhancements in WGM sensors: maximal when the two resonators
are detuned by half the plasmon linewidth. Approximate bounds are given to
quantify possible enhancements. Criteria for reactive vs. resistive coupling
are also established
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
Quasinormal-mode modeling and design in nonlinear nano-optics
Based on quasinormal-mode theory, we propose a novel approach enabling a deep
analytical insight into the multi-parameter design and optimization of
nonlinear photonic structures at subwavelength scale. A key distinction of our
method from previous formulations relying on multipolar Mie-scattering
expansions is that it directly exploits the natural resonant modes of the
nanostructures, which provide the field enhancement to achieve significant
nonlinear efficiency. Thanks to closed-form expression for the nonlinear
overlap integral between the interacting modes, we illustrate the potential of
our method with a two-order-of-magnitude boost of second harmonic generation in
a semiconductor nanostructure, by engineering both the sign of at
subwavelength scale and the structure of the pump beam
Nonradiative limitations to plasmon propagation in chains of metallic nanoparticles
We investigate the collective plasmonic modes in a chain of metallic
nanoparticles that are coupled by near-field interactions. The size- and
momentum-dependent nonradiative Landau damping and radiative decay rates are
calculated analytically within an open quantum system approach. These decay
rates determine the excitation propagation along the chain. In particular, the
behavior of the radiative decay rate as a function of the plasmon wavelength
leads to a transition from an exponential decay of the collective excitation
for short distances to an algebraic decay for large distances. Importantly, we
show that the exponential decay is of a purely nonradiative origin. Our
transparent model enables us to provide analytical expressions for the
polarization-dependent plasmon excitation profile along the chain and for the
associated propagation length. Our theoretical analysis constitutes an
important step in the quest for the optimal conditions for plasmonic
propagation in nanoparticle chains.Comment: 14 pages, 6 figures; v2: published versio
Optical anapoles in nanophotonics and meta-optics
Interference of electromagnetic modes supported by subwavelength photonic
structures is one of the key concepts that underpins the subwavelength control
of light in meta-optics. It drives the whole realm of all-dielectric
Mie-resonant nanophotonics with many applications for low-loss nanoscale
optical antennas, metasurfaces, and metadevices. Specifically, interference of
the electric and toroidal dipole moments results in a very peculiar,
low-radiating optical state associated with the concept of optical anapole.
Here, we uncover the physics of multimode interferences and multipolar
interplay in nanostructures with an intriguing example of the optical anapole.
We review the recently emerged field of anapole electrodynamics explicating its
relevance to multipolar nanophotonics, including direct experimental
observations, manifestations in nonlinear optics, and rapidly expanding
applications in nanoantennas, active photonics, and metamaterials.Comment: 14 pages, 6 figure
Three-dimensional integral equation approach to light scattering, extinction cross sections, local density of states, and quasi-normal modes
We present a numerical formalism for solving the Lippmann-Schwinger equation
for the electric field in three dimensions. The formalism may be applied to
scatterers of different shapes and embedded in different background media, and
we develop it in detail for the specific case of spherical scatterers in a
homogeneous background medium. In addition, we show how several physically
important quantities may readily be calculated with the formalism. These
quantities include the extinction cross section, the total Green's tensor, the
projected local density of states and the Purcell factor as well as the
quasinormal modes of leaky resonators with the associated resonance frequencies
and quality factors. We demonstrate the calculations for the well-known
plasmonic dimer consisting of two silver nanoparticles and thus illustrate the
versatility of the formalism for use in modeling of advanced nanophotonic
devices.Comment: 14 pages, 10 figures. Accepted for JOSA
Full-wave electromagnetic modes and hybridization in nanoparticle dimers
The plasmon hybridization theory is based on a quasi-electrostatic
approximation of the Maxwell's equations. It does not take into account
magnetic interactions, retardation effects, and radiation losses. Magnetic
interactions play a dominant role in the scattering from dielectric
nanoparticles. The retardation effects play a fundamental role in the coupling
of the modes with the incident radiation and in determining their radiative
strength; their exclusion may lead to erroneous predictions of the excited
modes and of the scattered power spectra. Radiation losses may lead to a
significant broadening of the scattering resonances. We propose a hybridization
theory for non-hermitian composite systems based on the full-Maxwell equations
that, overcoming all the limitations of the plasmon hybridization theory,
unlocks the description of dielectric dimers. As an example, we decompose the
scattered field from silicon and silver dimers, under different excitation
conditions and gap-sizes, in terms of dimer modes, pinpointing the hybridizing
isolated-sphere modes behind them.Comment: Supplemental material available upon reques
Dark modes and Fano resonances in plasmonic clusters excited by cylindrical vector beams
Control of the polarization distribution of light allows tailoring the electromagnetic response of plasmonic particles. By rigorously extending the generalized multiparticle Mie theory, we show that focused cylindrical vector beams (CVB) can be used to efficiently excite dark plasmon modes in nanoparticle clusters. In addition to the small radiative damping and large field enhancement associated to dark modes, excitation with CVB can give place to unusual phenomenology like the formation of electromagnetic cold spots and the generation of Fano resonances in highly symmetric clusters. Overall, the results show the potential of CVB to tailor the plasmonic response of nanoparticle clusters in a unique way
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