4,486 research outputs found

### Near field and far field scattering of surface plasmon polaritons by one-dimensional surface defects

A rigorous formulation for the scattering of surface plasmon polaritons (SPP)
from a one-dimensional surface defect of any shape that yields the
electromagnetic field in the vacuum half-space above the vacuum-metal interface
is developed by the use of an impedance boundary condition. The electric and
magnetic near fields, the angular distribution of the far-field radiation into
vacuum due to SPP-photon coupling, and the SPP reflection and transmission
coefficients are calculated by numerically solving the k-space integral
equation upon which the formulation is based. In particular, we consider
Gaussian-shaped defects and study the dependence of the above mentioned
physical quantities on their 1/e half-width a and height h. SPP reflection is
significant for narrow defects; maximum reflection (plasmon mirrors) is
achieved for a~lambda/10. For increasing defect widths, protuberances and
indentations behave differently. The former give rise to a monotonic increase
of radiation at the expense of SPP transmission for increasing defect
half-width. Indentations exhibit a significant increase of radiation (decrease
of SPP transmission) for half-widths of the order of or smaller than the
wavelength, but tend to total SPP transmission in an oscillatory manner upon
further increasing the half-width. Light-emitters might thus be associated with
either wide indentations, or protuberances with widths that are of the order of
or smaller than the wavelength.Comment: REVTeX 3.1, 10 pages with 9 EPS figures (epsf macro

### Lateral Casimir force beyond the Proximity Force Approximation

We argue that the appropriate variable to study a non trivial geometry
dependence of the Casimir force is the lateral component of the Casimir force,
which we evaluate between two corrugated metallic plates outside the validity
of the Proximity Force Approximation (PFA). The metallic plates are described
by the plasma model, with arbitrary values for the plasma wavelength, the plate
separation and the corrugation period, the corrugation amplitude remaining the
smallest length scale. Our analysis shows that in realistic experimental
situations the Proximity Force Approximation overestimates the force by up to
30%.Comment: 4 pages. Identical to v1, which was accidentally replaced by a
different paper (quant-ph/0610026

### Brewster quasi bound states in the continuum in all-dielectric metasurfaces from single magnetic-dipole resonance meta-atoms

Bound states in the continuum (BICs) are ubiquitous in many areas of physics,
attracting especial interest for their ability to confine waves with infinite
lifetimes. Metasurfaces provide a suitable platform to realize them in
photonics; such BICs are remarkably robust, being however complex to tune in
frequency-wavevector space.Here we propose a scheme to engineer BICs and
quasi-BICs with single magnetic-dipole resonance meta-atoms. Upon changing the
orientation of the magnetic-dipole resonances, we show that the resulting
quasi-BICs,emerging from the symmetry-protected BIC at normal incidence, become
transparent for plane-wave illumination exactly at the magnetic-dipole angle,
due to a Brewster-like effect. While yielding infinite Q-factors at
normalincidence(canonical BIC), these are termed Brewster quasi-BICs since a
transmission channel is always allowed that slightly widens resonances at
oblique incidences. This is demonstrated experimentally through reflectance
measurements in the microwave regime with high-refractive-index mm-disk
metasurfaces. Such Brewster-inspired configuration is a plausible scenario to
achieve quasi-BICs throughout the electromagnetic spectrum inaccessible through
plane-wave illumination at given angles, which could be extrapolated to other
kind of waves.Comment: 15 pages, 7 figures; typos corrected, Figs. 3 & 5 modified, new Fig.
7 & references adde

### Localized magnetic plasmons in all-dielectric mu<0 metastructures

Metamaterials are known to exhibit a variety of electromagnetic properties
non-existing in nature. We show that an all-dielectric (non-magnetic) system
consisting of deep subwavelength, high permittivity resonant spheres possess
effective negative magnetic permeability (dielectric permittivity being
positive and small). Due to the symmetry of the electromagnetic wave equations
in classical electrodynamics, localized "magnetic" plasmon resonances can be
excited in a metasphere made of such metamaterial. This is theoretically
demonstrated by the coupled-dipole approximation and numerically for real
spheres, in full agreement with the exact analytical solution for the
scattering process by the same metasphere with effective material properties
predicted by effective medium theory. The emergence of this phenomenon as a
function of structural order within the metastructures is also studied.
Universal conditions enabling effective negative magnetic permeability relate
subwavelength sphere permittivity and size with critical filling fraction. Our
proposal paves the way towards (all-dielectric) magnetic plasmonics, with a
wealth of fascinating applications.Comment: 7 pages, 4 figures; figure 3 modified and new figure (4) added, with
corresponding discussio

### Adaptive Optics Imaging of IRAS 18276-1431: a bipolar pre-planetary nebula with circumstellar "searchlight beams" and "arcs"

We present high-angular resolution images of the post-AGB nebula
IRAS18276-1431 (also known as OH17.7-2.0) obtained with the Keck II Adaptive
Optics (AO) system in its Natural Guide Star (NGS) mode in the Kp, Lp, and Ms
near-infrared bands. We also present supporting optical F606W and F814W HST
images as well as interferometric observations of the 12CO(J=1-0), 13CO(J=1-0),
and 2.6mm continuum emission with OVRO. The envelope of IRAS18276-1431 displays
a clear bipolar morphology in our optical and NIR images with two lobes
separated by a dark waist and surrounded by a faint 4.5"x3.4" halo. Our Kp-band
image reveals two pairs of radial ``searchlight beams'' emerging from the
nebula center and several intersecting, arc-like features. From our CO data we
derive a mass of M>0.38[D/3kpc]^2 Msun and an expansion velocity v_exp=17km/s
for the molecular envelope. The density in the halo follows a radial power-law
proportional to r^-3, which is consistent with a mass-loss rate increasing with
time. Analysis of the NIR colors indicates the presence of a compact central
source of ~300-500K dust illuminating the nebula in addition to the central
star. Modeling of the thermal IR suggests a two-shell structure in the dust
envelope: 1) an outer shell with inner and outer radius R_in~1.6E16cm and
R_out>~1.25E17cm, dust temperature T_d~105-50K, and a mean mass-loss rate of
Mdot~1E-3Msun/yr; and 2) an inner shell with R_in~6.3E14cm, T_dust~500-105K,
and Mdot~3E-5Msun/yr. An additional population of big dust grains (radius
a>~0.4mm) with T_dust=150-20K and mass M_dust=(0.16-1.6)E-3 [D/3kpc]^2 Msun can
account for the observed sub-mm and mm flux excess. The mass of the envelope
enclosed within R_out=1.25E17cm derived from SED modeling is ~1[D/3kpc]^2 Msun.Comment: 46 pages, 14 figures, 3 tables, accepted for publication in ApJ.
Figures 12 & 13 in low resolution. Full resolution versions are available
upon request to the first autho

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