516 research outputs found
Mean Field Theory for Lossy Nonlinear Composites
The mean-field theory for lossy nonlinear composites, described by complex
and field-dependent dielectric functions, is presented. By using the spectral
representation of linear composites with identical microstructure, we develop
self-consistent equations for the effective response. We examine two types of
microstructure, namely, the Maxwell-Garnett approximation and the effective
medium approximation to illustrate the theory.Comment: 11 pages, LaTeX format, 2 figures, accepted for publication by Solid
State Communications 18 November 199
Tunneling mechanism of light transmission through metallic films
A mechanism of light transmission through metallic films is proposed,
assisted by tunnelling between resonating buried dielectric inclusions. This is
illustrated by arrays of Si spheres embedded in Ag. Strong transmission peaks
are observed near the Mie resonances of the spheres. The interaction among
various planes of spheres and interference effects between these resonances and
the surface plasmons of Ag lead to mixing and splitting of the resonances.
Transmission is proved to be limited only by absorption. For small spheres, the
effective dielectric constant can be tuned to values close to unity and a
method is proposed to turn the resulting materials invisible.Comment: 4 papges, 5 figure
Interface modes of two-dimensional composite structures
The surface modes of a composite consisting of aligned metallic wires with
square cross sections are investigated, on the basis of photonic band structure
calculations. The effective long-wavelength dielectric response function is
computed, as a function of the filling fraction. The dependence of the optical
absorption on the shape of the wires and the polarization of light is
discussed, and the effect of sharp corners analyzed. The effect of the
interaction between the wires on the localization of surface plasmons is also
addressed.Comment: 12 pages, 4 figures, to appear in Surf. Sc
The calculation of thin film parameters from spectroscopic ellipsometry data
Spectroscopic ellipsometry (SE) has proven to be a very powerful diagnostic for thin film characterization, but the results of SE experiments must first be compared with calculations to determine thin film parameters such as film thickness and optical functions. This process requires 4 steps: (1) The quantities measured must be specified and the equivalent calculated parameters identified. (2) The film structure must be modeled, where the number of films is specified and certain characteristics of each layer specified, such as whether or not the film is isotropic or anisotropic, homogeneous or graded. (3) The optical functions of each layer must be specified or parameterized. (4) The data must be compared with the calculated spectra, where a quantifiable figure of merit is used for the comparison. The last step is particularly important because without it, no {open_quotes}goodness of fit{close_quotes} parameter is calculated and one does not know whether or not the calculated spectrum fits the data
Electronic response of aligned multishell carbon nanotubes
We report calculations of the effective electronic response of aligned
multishell carbon nanotubes. A local graphite-like dielectric tensor is
assigned to every point of the multishell tubules, and the effective transverse
dielectric function of the composite is computed by solving Maxwell's
equations. Calculations of both real and imaginary parts of the effective
dielectric function are presented, for various values of the filling fraction
and the ratio of the internal and external radii of hollow tubules. Our full
calculations indicate that the experimentally measured macroscopic dielectric
function of carbon nanotube materials is the result of a strong electromagnetic
coupling between the tubes, which cannot be accounted for with the use of
simplified effective medium theories. The presence of surface plasmons is
investigated, and both optical absorption cross sections and energy-loss
spectra of aligned tubules are calculated.Comment: 4 pages, 4 figures, to appear in Phys. Rev.
Electron energy loss and induced photon emission in photonic crystals
The interaction of a fast electron with a photonic crystal is investigated by
solving the Maxwell equations exactly for the external field provided by the
electron in the presence of the crystal. The energy loss is obtained from the
retarding force exerted on the electron by the induced electric field. The
features of the energy loss spectra are shown to be related to the photonic
band structure of the crystal. Two different regimes are discussed: for small
lattice constants relative to the wavelength of the associated electron
excitations , an effective medium theory can be used to describe the
material; however, for the photonic band structure plays an
important role. Special attention is paid to the frequency gap regions in the
latter case.Comment: 12 pages, 7 figure
Effective electronic response of a system of metallic cylinders
The electronic response of a composite consisting of aligned metallic
cylinders in vacuum is investigated, on the basis of photonic band structure
calculations. The effective long-wavelength dielectric response function is
computed, as a function of the filling fraction. A spectral representation of
the effective response is considered, and the surface mode strengths and
positions are analyzed. The range of validity of a Maxwell-Garnett-like
approach is discussed, and the impact of our results on absorption spectra and
electron energy-loss phenomena is addressed.Comment: 15 pages, 6 figures, to appear in Phys. Rev.
Homogenization of nonlocal wire metamaterial via a renormalization approach
It is well known that defining a local refractive index for a metamaterial
requires that the wavelength be large with respect to the scale of its
microscopic structure (generally the period). However, the converse does not
hold. There are simple structures, such as the infinite, perfectly conducting
wire medium, which remain non-local for arbitrarily large wavelength-to-period
ratios. In this work we extend these results to the more realistic and relevant
case of finite wire media with finite conductivity. In the quasi-static regime
the metamaterial is described by a non-local permittivity which is obtained
analytically using a two-scale renormalization approach. Its accuracy is tested
and confirmed numerically via full vector 3D finite element calculations.
Moreover, finite wire media exhibit large absorption with small reflection,
while their low fill factor allows considerable freedom to control other
characteristics of the metamaterial such as its mechanical, thermal or chemical
robustness.Comment: 8 pages on two columns, 7 figures, submitted to Phys. Rev.
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