1,369 research outputs found
Sub-diffraction light propagation in fibers with anisotropic dielectric cores
We present a detailed study of light propagation in waveguides with
anisotropic metamaterial cores. We demonstrate that in contrast to conventional
optical fibers, our structures support free-space-like propagating modes even
when the waveguide radius is much smaller than the wavelength. We develop
analytical formalism to describe mode structure and propagation in strongly
anisotropic systems and study the effects related to waveguide boundaries and
material composition
A study of long range order in certain two-dimensional frustrated lattices
We have studied the Heisenberg antiferromagnets on two-dimensional frustrated
lattices, triangular and kagome lattices using linear spin-wave theory. A
collinear ground state ordering is possible if one of the three bonds in each
triangular plaquette of the lattice becomes weaker or frustrated. We study
spiral order in the Heisenberg model along with Dzyaloshinskii-Moriya (DM)
interaction and in the presence of a magnetic field. The quantum corrections to
the ground state energy and sublattice magnetization are calculated
analytically in the case of triangular lattice with nearesr-neighbour
interaction. The corrections depend on the DM interaction strength and the
magnetic field. We find that the DM interaction stabilizes the long-range
order, reducing the effect of quantum fluctuations. Similar conclusions are
reached for the kagome lattice. We work out the linear spin-wave theory at
first with only nearest-neighbour (nn) terms for the kagome lattice. We find
that the nn interaction is not sufficient to remove the effects of low energy
fluctuations. The flat branch in the excitation spectrum becomes dispersive on
addition of furthet neighbour interactions. The ground state energy and the
excitation spectrum have been obtained for various cases.Comment: 18 pages, 9 figure
Improved success rate and stability for phase retrieval by including randomized overrelaxation in the hybrid input output algorithm
In this paper, we study the success rate of the reconstruction of objects of
finite extent given the magnitude of its Fourier transform and its geometrical
shape. We demonstrate that the commonly used combination of the hybrid input
output and error reduction algorithm is significantly outperformed by an
extension of this algorithm based on randomized overrelaxation. In most cases,
this extension tremendously enhances the success rate of reconstructions for a
fixed number of iterations as compared to reconstructions solely based on the
traditional algorithm. The good scaling properties in terms of computational
time and memory requirements of the original algorithm are not influenced by
this extension.Comment: 14 pages, 8 figure
Morphological instabilities of a thin film on a Penrose lattice: a Monte Carlo study
We computed by a Monte Carlo method the thermal relaxation of a
polycrystalline thin film deposited on a Penrose lattice. The thin film was
modelled by a 2 dimensional array of elementary domains, which have each a
given height. During the Monte Carlo process, the height of each of these
elementary domains is allowed to change as well as their crystallographic
orientation. After equilibrium is reached at a given numerical temperature, all
elementary domains have changed their orientation into the same one and small
islands appear, preferentially on the domains of the Penrose lattice located in
the center of heptagons. This method is a new numerical approach to study the
influence of the substrate and its defects on the islanding process of
polycrystalline films.Comment: 9 pages,5 figure
Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers
Guided Acoustic Wave Brillouin Scattering (GAWBS) generates phase and
polarization noise of light propagating in glass fibers. This excess noise
affects the performance of various experiments operating at the quantum noise
limit. We experimentally demonstrate the reduction of GAWBS noise in a photonic
crystal fiber in a broad frequency range using cavity sound dynamics. We
compare the noise spectrum to the one of a standard fiber and observe a 10-fold
noise reduction in the frequency range up to 200 MHz. Based on our measurement
results as well as on numerical simulations we establish a model for the
reduction of GAWBS noise in photonic crystal fibers.Comment: 4 pages, 7 figures; added numerical simulations, added reference
Scattering-free plasmonic optics with anisotropic metamaterials
We develop an approach to utilize anisotropic metamaterials to solve one of
the fundamental problems of modern plasmonics -- parasitic scattering of
surface waves into free-space modes, opening the road to truly two-dimensional
plasmonic optics. We illustrate the developed formalism on examples of
plasmonic refractor and plasmonic crystal, and discuss limitations of the
developed technique and its possible applications for sensing and imaging
structures, high-performance mode couplers, optical cloaking structures, and
dynamically reconfigurable electro-plasmonic circuits
Magnetic Properties of Undoped
The Heisenberg antiferromagnet, which arises from the large Hubbard
model, is investigated on the molecule and other fullerenes. The
connectivity of leads to an exotic classical ground state with
nontrivial topology. We argue that there is no phase transition in the Hubbard
model as a function of , and thus the large solution is relevant for
the physical case of intermediate coupling. The system undergoes a first order
metamagnetic phase transition. We also consider the S=1/2 case using
perturbation theory. Experimental tests are suggested.Comment: 12 pages, 3 figures (included
Stability of the hard-sphere icosahedral quasilattice
The stability of the hard-sphere icosahedral quasilattice is analyzed using
the differential formulation of the generalized effective liquid approximation.
We find that the icosahedral quasilattice is metastable with respect to the
hard-sphere crystal structures. Our results agree with recent findings by
McCarley and Ashcroft [Phys. Rev. B {\bf 49}, 15600 (1994)] carried out using
the modified weighted density approximation.Comment: 15 pages, 2 figures available from authors upon request, (revtex),
submitted to Phys. Rev.
Quasi-planar optics: computing light propagation and scattering in planar waveguide arrays
We analyze wave propagation in coupled planar waveguides, pointing specific
attention to modal cross-talk and out-of-plane scattering in quasi-planar
photonics. An algorithm capable of accurate numerical computation of wave
coupling in arrays of planar structures is developed and illustrated on several
examples of plasmonic and volumetric waveguides. An analytical approach to
reduce or completely eliminate scattering and modal cross-talk in planar
waveguides with anisotropic materials is also presented
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