921 research outputs found
Large tunable photonic band gaps in nanostructured doped semiconductors
A plasmonic nanostructure conceived with periodic layers of a doped
semiconductor and passive semiconductor is shown to generate spontaneously
surface plasmon polaritons thanks to its periodic nature. The nanostructure is
demonstrated to behave as an effective material modeled by a simple dielectric
function of ionic-crystal type, and possesses a fully tunable photonic band
gap, with widths exceeding 50%, in the region extending from mid-infra-red to
Tera-Hertz.Comment: 6 pages, 4 figures, publishe
The onset of tree-like patterns in negative streamers
We present the first analytical and numerical studies of the initial stage of
the branching process based on an interface dynamics streamer model in the
fully 3-D case. This model follows from fundamental considerations on charge
production by impact ionization and balance laws, and leads to an equation for
the evolution of the interface between ionized and non-ionized regions. We
compare some experimental patterns with the numerically simulated ones, and
give an explicit expression for the growth rate of harmonic modes associated
with the perturbation of a symmetrically expanding discharge. By means of full
numerical simulation, the splitting and formation of characteristic tree-like
patterns of electric discharges is observed and described
Surface Josephson plasma waves in layered superconductors
We predict the existence of surface waves in layered superconductors in the
THz frequency range, below the Josephson plasma frequency . This wave
propagates along the vacuum-superconductor interface and dampens in both
transverse directions out of the surface (i.e., towards the superconductor and
towards the vacuum). This is the first prediction of propagating surface waves
in any superconductor. These predicted surface Josephson plasma waves are
important for different phenomena, including the complete suppression of the
specular reflection from a sample (Wood's anomalies) and a huge enhancement of
the wave absorption (which can be used as a THz detector).Comment: 4 pages, 2 figure
Perfect coupling of light to surface plasmons with ultra-narrow linewidths
We examine the coupling of electromagnetic waves incident normal to a thin
silver film that forms an oscillatory grating embedded between two otherwise
uniform, semi-infinite half spaces. Two grating structures are considered, in
one of which the mid point of the Ag film remains fixed whereas the thickness
varies sinusoidally, while in the other the mid point oscillates sinusoidally
whereas the film thicknesses remains fixed. On reducing the light wavelength
from the long wavelength limit, we encounter signatures in the transmission, T,
and reflection, R, coefficients associated with: i) the short-range surface
plasmon mode, ii) the long-range surface plasmon mode, and iii) electromagnetic
diffraction tangent to the grating. The first two features can be regarded as
generalized (plasmon) Wood's anomalies whereas the third is the first-order
conventional (electromagnetic) Wood's anomaly. The energy density at the film
surface is enhanced for wavelengths corresponding to these three anomalies,
particularly for the long range plasmon mode in thin films. When exciting the
silver film with a pair of waves incident from opposite directions, we find
that by adjusting the grating oscillation amplitude and fixing the relative
phase of the incoming waves to be even or odd, T+R can be made to vanish for
one or the other of the plasmon modes; this corresponds to perfect coupling
(impedance matching in the language of electrical engineering) between the
incoming light and these modes.Comment: 13 pages, 5 figures. accepted J. Chem. Phy
Gain-assisted slow to superluminal group velocity manipulation in nano-waveguides
We study the energy propagation in subwavelength waveguides and demonstrate
that the mechanism of material gain, previously suggested for loss
compensation, is also a powerful tool to manipulate dispersion and propagation
characteristics of electromagnetic pulses at the nanoscale. We show
theoretically that the group velocity in lossy nano-waveguides can be
controlled from slow to superluminal values by the material gain and waveguide
geometry and develop an analytical description of the relevant physics. We
utilize the developed formalism to show that gain-assisted dispersion
management can be used to control the transition between ``photonic-funnel''
and ``photonic-compressor'' regimes in tapered nano-waveguides. The phenomenon
of strong modulation of group velocity in subwavelength structures can be
realized in waveguides with different geometries, and is present for both
volume and surface-modes.Comment: Some changes in the abstract and Fig.1. No results affecte
Enhanced transmission of optically thick metallic films at infrared wavelengths
For an optically thick metallic film, the transmission for both s- and
p-polarized waves is extremely low. If the metallic film is coated on both
sides with a finite dielectric layer, light transmission for -polarized
waves can be enhanced considerably. This enhancement is not related to surface
plasmon-polaritions. Instead, it is due to the interplay between Fabry-Perot
interference in the coated dielectric layer and the existence of the Brewster
angle at the dielectric/metallic interface. It is shown that the coated
metallic films can act as excellent polarizers at infrared wavelengths.Comment: 3 pages, 4 figures. Submitted to Appl. Phys. Let
Theory of Optical Transmission through Elliptical Nanohole Arrays
We present a theory which explains (in the quasistatic limit) the
experimentally observed [R. Gordon, {\it et al}, Phys. Rev. Lett. {\bf 92},
037401 (2004)] squared dependence of the depolarization ratio on the aspect
ratio of the holes, as well as other features of extraordinary light
transition. We calculated the effective dielectric tensor of a metal film
penetrated by elliptical cylindrical holes and found the extraordinarily light
transmission at special frequencies related to the surface plasmon resonances
of the composite film. We also propose to use the magnetic field for getting a
strong polarization effect, which depends on the ratio of the cyclotron to
plasmon frequencies.Comment: 4 pages, 4 figure
Conversion of terahertz wave polarization at the boundary of a layered superconductor due to the resonance excitation of oblique surface waves
We predict a complete TM-TE transformation of the polarization of terahertz
electromagnetic waves reflected from a strongly anisotropic boundary of a
layered superconductor. We consider the case when the wave is incident on the
superconductor from a dielectric prism separated from the sample by a thin
vacuum gap. The physical origin of the predicted phenomenon is similar to the
Wood anomalies known in optics, and is related to the resonance excitation of
the oblique surface waves. We also discuss the dispersion relation for these
waves, propagating along the boundary of the superconductor at some angle with
respect to the anisotropy axis, as well as their excitation by the
attenuated-total-reflection method.Comment: 4 pages, 5 figure
Direct generation of charge carriers in c-Si solar cells due to embedded nanoparticles
It is known that silicon is an indirect band gap material, reducing its
efficiency in photovoltaic applications. Using surface plasmons in metallic
nanoparticles embedded in a solar cell has recently been proposed as a way to
increase the efficiency of thin film silicon solar cells. The dipole mode that
dominates the plasmons in small particles produces an electric field having
Fourier components with all wave numbers. In this work, we show that such a
field creates electron-hole-pairs without phonon assistance, and discuss the
importance of this effect compared to radiation from the particle and losses
due to heating.Comment: 1 figur
Generalized scattering-matrix approach for magneto-optics in periodically patterned multilayer systems
We present here a generalization of the scattering-matrix approach for the
description of the propagation of electromagnetic waves in nanostructured
magneto-optical systems. Our formalism allows us to describe all the key
magneto-optical effects in any configuration in periodically patterned
multilayer structures. The method can also be applied to describe periodic
multilayer systems comprising materials with any type of optical anisotropy. We
illustrate the method with the analysis of a recent experiment in which the
transverse magneto-optical Kerr effect was measured in a Fe film with a
periodic array of subwavelength circular holes. We show, in agreement with the
experiments, that the excitation of surface plasmon polaritons in this system
leads to a resonant enhancement of the transverse magneto-optical Kerr effect.Comment: 12 pages, 6 figures, submitted to Physical Review
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