346 research outputs found
Giant radiation heat transfer through the micron gaps
Near-field heat transfer between two closely spaced radiating media can
exceed in orders radiation through the interface of a single black body. This
effect is caused by exponentially decaying (evanescent) waves which form the
photon tunnel between two transparent boundaries. However, in the mid-infrared
range it holds when the gap between two media is as small as few tens of
nanometers. We propose a new paradigm of the radiation heat transfer which
makes possible the strong photon tunneling for micron thick gaps. For it the
air gap between two media should be modified, so that evanescent waves are
transformed inside it into propagating ones. This modification is achievable
using a metamaterial so that the direct thermal conductance through the
metamaterial is practically absent and the photovoltaic conversion of the
transferred heat is not altered by the metamaterial.Comment: 4 pages, 3 figure
Second-order calculation of the local density of states above a nanostructured surface
We have numerically implemented a perturbation series for the scattered
electromagnetic fields above rough surfaces, due to Greffet, allowing us to
evaluate the local density of states to second order in the surface profile
function. We present typical results for thermal near fields of surfaces with
regular nanostructures, investigating the relative magnitude of the
contributions appearing in successive orders. The method is then employed for
estimating the resolution limit of an idealized Near-Field Scanning Thermal
Microscope (NSThM).Comment: 10 pages, 7 figure
Microscopic model of Purcell enhancement in hyperbolic metamaterials
We study theoretically a dramatic enhancement of spontaneous emission in
metamaterials with the hyperbolic dispersion modeled as a cubic lattice of
anisotropic resonant dipoles. We analyze the dependence of the Purcell factor
on the source position in the lattice unit cell and demonstrate that the
optimal emitter position to achieve large Purcell factors and Lamb shifts are
in the local field maxima. We show that the calculated Green function has a
characteristic cross-like shape, spatially modulated due to structure
discreteness. Our basic microscopic theory provides fundamental insights into
the rapidly developing field of hyperbolic metamaterials.Comment: 9 pages, 11 figure
Spontaneous radiation of a finite-size dipole emitter in hyperbolic media
We study the radiative decay rate and Purcell effect for a finite-size dipole
emitter placed in a homogeneous uniaxial medium. We demonstrate that the
radiative rate is strongly enhanced when the signs of the longitudinal and
transverse dielectric constants of the medium are opposite, and the
isofrequency contour has a hyperbolic shape. We reveal that the Purcell
enhancement factor remains finite even in the absence of losses, and it depends
on the emitter size.Comment: 6 pages, 3 figure
Oblique launching of optical surface waves by a subwavelength slit
The electromagnetic field on the metal surface launched by a subwavelength
slit is analytically studied, for the case when the fundamental mode inside the
slit has a wavevector component along the slit axis (conical mount). Both
near-field and far-field regions are discussed, and the role of surface
plasmon-polaritons and Norton waves is revealed. It is shown that the distance
from the slit at which NW are more intense than surface plasmons decrease with
parallel wavevector, which could help experimental studies on Norton waves.
Additionally, it is found that the s-polarization component, while present for
any non-zero parallel wavevector, only weakly contributes to the NWs.Comment: 8 pages, 5 figure
Diffraction by a small aperture in conical geometry: Application to metal coated tips used in near-field scanning optical microscopy
Light diffraction through a subwavelength aperture located at the apex of a
metallic screen with conical geometry is investigated theoretically. A method
based on a multipole field expansion is developed to solve Maxwell's equations
analytically using boundary conditions adapted both for the conical geometry
and for the finite conductivity of a real metal. The topological properties of
the diffracted field are discussed in detail and compared to those of the field
diffracted through a small aperture in a flat screen, i. e. the Bethe problem.
The model is applied to coated, conically tapered optical fiber tips that are
used in Near-Field Scanning Optical Microscopy. It is demonstrated that such
tips behave over a large portion of space like a simple combination of two
effective dipoles located in the apex plane (an electric dipole and a magnetic
dipole parallel to the incident fields at the apex) whose exact expressions are
determined. However, the large "backward" emission in the P plane - a salient
experimental fact that remained unexplained so far - is recovered in our
analysis which goes beyond the two-dipole approximation.Comment: 21 pages, 6 figures, published in PRE in 200
At Wisdom’s Table: How Narrative Shapes the Biblical Food Laws and Their Social Function
This second part of a two-paper sequence deals with the physical interpretation of the rigorously derived high-frequency asymptotic wave-field solution in Part I, pertaining to a semi-infinite phased array of parallel dipole radiators. The asymptotic solution contains two parts that represent contributions due to truncated Floquet waves (FW's) and to the corresponding edge diffractions, respectively. The phenomenology of the FW-excited diffracted fields is discussed in detail. All possible combinations of propagating (radiating) and evanescent (nonradiating) FW and diffracted contributions are considered. The format is a generalization of the conventional geometrical theory of diffraction (GTD) for smooth truncated aperture distributions to the truncated periodicity-induced FW distributions with their corresponding FW-modulated edge diffractions. Ray paths for propagating diffracted waves are defined according to a generalized Fermât principle, which is also valid by analytic continuation for evanescent diffracted ray fields. The mechanism of uniform compensation for the FW-field discontinuities (across their truncation shadow boundaries) by the diffracted waves is explored for propagating and evanescent FW's, including the cutoff transition from the propagating to the evanescent regime for both the FW and diffracted constituents. Illustrative examples demonstrate: 1) the accuracy and efficiency of the high-frequency algorithm under conditions that involve the various wave processes outlined above and 2) the cogent interpretation of the results in terms of the uniform FW-modulated GTD. ©2000 IEEE
In the diffraction shadow: Norton waves versus surface plasmon-polaritons in the optical region
Surface electromagnetic modes supported by metal surfaces have a great
potential for uses in miniaturised detectors and optical circuits. For many
applications these modes are excited locally. In the optical regime, Surface
Plasmon Polaritons (SPPs) have been thought to dominate the fields at the
surface, beyond a transition region comprising 3-4 wavelengths from the source.
In this work we demonstrate that at sufficiently long distances SPPs are not
the main contribution to the field. Instead, for all metals, a different type
of wave prevails, which we term Norton waves for their reminiscence to those
found in the radio-wave regime at the surface of the Earth. Our results show
that Norton Waves are stronger at the surface than SPPs at distances larger
than 6-9 SPP's absorption lengths, the precise value depending on wavelength
and metal. Moreover, Norton waves decay more slowly than SPPs in the direction
normal to the surface.Comment: 8 pages, 8 figure
Transmutations and spectral parameter power series in eigenvalue problems
We give an overview of recent developments in Sturm-Liouville theory
concerning operators of transmutation (transformation) and spectral parameter
power series (SPPS). The possibility to write down the dispersion
(characteristic) equations corresponding to a variety of spectral problems
related to Sturm-Liouville equations in an analytic form is an attractive
feature of the SPPS method. It is based on a computation of certain systems of
recursive integrals. Considered as families of functions these systems are
complete in the -space and result to be the images of the nonnegative
integer powers of the independent variable under the action of a corresponding
transmutation operator. This recently revealed property of the Delsarte
transmutations opens the way to apply the transmutation operator even when its
integral kernel is unknown and gives the possibility to obtain further
interesting properties concerning the Darboux transformed Schr\"{o}dinger
operators.
We introduce the systems of recursive integrals and the SPPS approach,
explain some of its applications to spectral problems with numerical
illustrations, give the definition and basic properties of transmutation
operators, introduce a parametrized family of transmutation operators, study
their mapping properties and construct the transmutation operators for Darboux
transformed Schr\"{o}dinger operators.Comment: 30 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1111.444
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