170 research outputs found
Band gap engineering in simultaneous phononic and photonic crystal slabs
We discuss the simultaneous existence of phononic and photonic band gaps in two types of phononic crystals
slabs, namely periodic arrays of nanoholes in a Si membrane
and of Si nanodots on a SiO2 membrane. In the former
geometry, we investigate in detail both the boron nitride
lattice and the square lattice with two atoms per unit cell
(these include the square, triangular and honeycomb lattices
as particular cases). In the latter geometry, some preliminary
results are reported for a square lattice
Phonon-Plasmon Interaction in Metal-Insulator-Metal Localized Surface Plasmon Systems
We investigate theoretically and numerically the coupling between elastic and
localized surface plasmon modes in a system of gold nanocylinders separated
from a thin gold film by a dielectric spacer of few nanometers thickness. That
system supports plasmon modes confined in between the bottom of the
nanocylinder and the top of the gold film, which arise from the formation of
interference patterns by short-wavelength metal-insulator-metal propagating
plasmon. First we present the plasmonic properties of the system though
computer-simulated extinction spectra and field maps associated to the
different optical modes. Next a simple analytical model is introduced, which
allows to correctly reproduce the shape and wavelengths of the plasmon modes.
This model is used to investigate the efficiency of the coupling between an
elastic deformation and the plasmonic modes. In the last part of the paper, we
present the full numerical simulations of the phononic properties of the
system, and then compute the acousto-plasmonic coupling between the different
plasmon modes and five acoustic modes of very different shape. The efficiency
of the coupling is assessed first by evaluating the modulation of the resonance
wavelength, which allows comparison with the analytical model, and finally in
term of time-modulation of the transmission spectra on the full visible range,
computed for realistic values of the deformation of the nanoparticle.Comment: 12 pages, 9 figure
Equilibria of large random Lotka-Volterra systems with vanishing species: a mathematical approach
Ecosystems that consist in a large number of species are often modelled as
Lotka-Volterra dynamical systems built around a large random interaction
matrix. Under some known conditions, global equilibria exist for such dynamical
systems. This paper is devoted towards studying rigorously the asymptotic
behavior of the distribution of the elements of a global equilibrium vector in
the regime of large dimensions. Such a vector is known to be the solution of a
so-called Linear Complementarity Problem. It is shown here that the large
dimensional distribution of such a solution can be estimated with the help of
an Approximate Message Passing (AMP) approach, a technique that has recently
aroused an intense research effort in the fields of statistical physics,
Machine Learning, or communication theory. Interaction matrices taken from the
Gaussian Orthogonal Ensemble, or following a Wishart distribution are
considered. Beyond these models, the AMP approach developed in this paper has
the potential to address more involved interaction matrix models for solving
the problem of the asymptotic distribution of the equilibria
Dual phononic and photonic band gaps in a periodic array of pillars deposited on a thin plate
We study theoretically the simultaneous existence of phononic and photonic band gaps in a periodic array of
silicon pillars deposited on a homogeneous thin silica plate. Several lattices, namely, square, triangular, and
honeycomb are investigated for a wide range of geometrical parameters. We discuss the most suitable cases for
dual phononic-photonic band gaps, especially in comparison to the more conventional structures constituted by
a periodic array of holes in a membrane
Wave propagation in a quasi-periodic waveguide network
We investigate the transport properties of a classical wave propagating
through a quasi-periodic Fibonacci array of waveguide segments in the form of
loops. The formulation is general, and applicable for electromagnetic or
acoustic waves through such structures. We examine the conditions for resonant
transmission in a Fibonacci waveguide structure. The local positional
correlation between the loops are found to be responsible for the resonance. We
also show that, depending on the number of segments attached to a particular
loop, the intensity at the nodes displays a perfectly periodic or a
self-similar pattern. The former pattern corresponds to a perfectly extended
mode of propagation, which is to be contrasted to the electron or phonon
characteristics of a pure one dimensional Fibonacci quasi-crystal.Comment: 15 pages, 5 figure
Unusual modes and photonic gaps in a Vicsek waveguide network
We propose a simple model of a waveguide network designed following the
growth rule of a Vicsek fractal. We show, within the framework of real space
renormalization group (RSRG) method, that such a design may lead to the
appearance of unusual electromagnetic modes. Such modes exhibit an extended
character in RSRG sense. However, they lead to a power law decay in the
end-to-end transmission of light across such a network model as the size of the
network increases. This, to our mind, may lead to an observation of power law
localization of light in a fractal waveguide network. The general occurence of
photonic band gaps and their change as a function of the parameters of the
system are also discussed.Comment: 13 pages, 6 figure
Angular plasmon response of gold nanoparticles arrays: approaching the Rayleigh limit
AbstractThe regular arrangement of metal nanoparticles influences their plasmonic behavior. It has been previously demonstrated that the coupling between diffracted waves and plasmon modes can give rise to extremely narrow plasmon resonances. This is the case when the single-particle localized surface plasmon resonance (λLSP) is very close in value to the Rayleigh anomaly wavelength (λRA) of the nanoparticles array. In this paper, we performed angle-resolved extinction measurements on a 2D array of gold nano-cylinders designed to fulfil the condition λRA<λLSP. Varying the angle of excitation offers a unique possibility to finely modify the value of λRA, thus gradually approaching the condition of coupling between diffracted waves and plasmon modes. The experimental observation of a collective dipolar resonance has been interpreted by exploiting a simplified model based on the coupling of evanescent diffracted waves with plasmon modes. Among other plasmon modes, the measurement technique has also evidenced and allowed the study of a vertical plasmon mode, only visible in TM polarization at off-normal excitation incidence. The results of numerical simulations, based on the periodic Green's tensor formalism, match well with the experimental transmission spectra and show fine details that could go unnoticed by considering only experimental data
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