3,278 research outputs found
Comparison of imaging with sub-wavelength resolution in the canalization and resonant tunnelling regimes
We compare the properties of subwavelength imaging in the visible wavelength
range for metal-dielectric multilayers operating in the canalization and the
resonant tunnelling regimes. The analysis is based on the transfer matrix
method and time domain simulations. We show that Point Spread Functions for the
first two resonances in the canalization regime are approximately Gaussian in
shape. Material losses suppress transmission for higher resonances, regularise
the PSF but do not compromise the resolution. In the resonant tunnelling
regime, the MTF may dramatically vary in their phase dependence. Resulting PSF
may have a sub-wavelength thickness as well as may be broad with multiple
maxima and a rapid phase modulation. We show that the width of PSF may be
reduced by further propagation in free space, and we provide arguments to
explain this surprising observation.Comment: 17 pages,12 figure
Born-Regulated Gravity in Four Dimensions
Previous work involving Born-regulated gravity theories in two dimensions is
extended to four dimensions. The action we consider has two dimensionful
parameters. Black hole solutions are studied for typical values of these
parameters. For masses above a critical value determined in terms of these
parameters, the event horizon persists. For masses below this critical value,
the event horizon disappears, leaving a ``bare mass'', though of course no
singularity.Comment: LaTeX, 15 pages, 2 figure
Trapped Ion Imaging with a High Numerical Aperture Spherical Mirror
Efficient collection and analysis of trapped ion qubit fluorescence is
essential for robust qubit state detection in trapped ion quantum computing
schemes. We discuss simple techniques of improving photon collection efficiency
using high numerical aperture (N.A.) reflective optics. To test these
techniques we placed a spherical mirror with an effective N.A. of about 0.9
inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate
stable and reliable trapping of single barium ions, in excellent agreement with
our simulations of the electric field in this setup. While a large N.A.
spherical mirror introduces significant spherical aberration, the ion image
quality can be greatly improved by a specially designed aspheric corrector lens
located outside the vacuum system. Our simulations show that the spherical
mirror/corrector design is an easy and cost-effective way to achieve high
photon collection rates when compared to a more sophisticated parabolic mirror
setup.Comment: 5 figure
Casimir-Polder interatomic potential between two atoms at finite temperature and in the presence of boundary conditions
We evaluate the Casimir-Polder potential between two atoms in the presence of
an infinite perfectly conducting plate and at nonzero temperature. In order to
calculate the potential, we use a method based on equal-time spatial
correlations of the electric field, already used to evaluate the effect of
boundary conditions on interatomic potentials. This method gives also a
transparent physical picture of the role of a finite temperature and boundary
conditions on the Casimir-Polder potential. We obtain an analytical expression
of the potential both in the near and far zones, and consider several limiting
cases of interest, according to the values of the parameters involved, such as
atom-atom distance, atoms-wall distance and temperature.Comment: 11 page
On the physical origins of the negative index of refraction
The physical origins of negative refractive index are derived from a dilute
microscopic model, producing a result that is generalized to the dense
condensed phase limit. In particular, scattering from a thin sheet of electric
and magnetic dipoles driven above resonance is used to form a fundamental
description for negative refraction. Of practical significance, loss and
dispersion are implicit in the microscopic model. While naturally occurring
negative index materials are unavailable, ferromagnetic and ferroelectric
materials provide device design opportunities.Comment: 4 pages, 1 figur
Evaluation of Born and local effective charges in unoriented materials from vibrational spectra
We present an application of the Lorentz model in which fits to vibrational
spectra or a Kramers Kronig analysis are employed along with several useful
formalisms to quantify microscopic charge in unoriented (powdered) materials.
The conditions under which these techniques can be employed are discussed, and
we analyze the vibrational response of a layered transition metal
dichalcogenide and its nanoscale analog to illustrate the utility of this
approach.Comment: 9 pages, 1 figur
Inelastic Diffraction and Spectroscopy of Very Weakly Bound Clusters
We study the coherent inelastic diffraction of very weakly bound two body
clusters from a material transmission grating. We show that internal
transitions of the clusters can lead to new separate peaks in the diffraction
pattern whose angular positions determine the excitation energies. Using a
quantum mechanical approach to few body scattering theory we determine the
relative peak intensities for the diffraction of the van der Waals dimers
(D_2)_2 and H_2-D_2. Based on the results for these realistic examples we
discuss the possible applications and experimental challenges of this coherent
inelastic diffraction technique.Comment: 15 pages + 5 figures. J. Phys. B (in press
Diagonalization of multicomponent wave equations with a Born-Oppenheimer example
A general method to decouple multicomponent linear wave equations is presented. First, the Weyl calculus is used to transform operator relations into relations between c-number valued matrices. Then it is shown that the symbol representing the wave operator can be diagonalized systematically up to arbitrary order in an appropriate expansion parameter. After transforming the symbols back to operators, the original problem is reduced to solving a set of linear uncoupled scalar wave equations. The procedure is exemplified for a particle with a Born-Oppenheimer-type Hamiltonian valid through second order in h. The resulting effective scalar Hamiltonians are seen to contain an additional velocity-dependent potential. This contribution has not been reported in recent studies investigating the adiabatic motion of a neutral particle moving in an inhomogeneous magnetic field. Finally, the relation of the general method to standard quantum-mechanical perturbation theory is discussed
Spin-filter effect of the europium chalcogenides: An exactly solved many-body model
A model Hamiltonian is introduced which considers the main features of the
experimental spin filter situation as s-f interaction, planar geometry and the
strong external electric field. The proposed many-body model can be solved
analytically and exactly using Green functions.
The spin polarization of the field-emitted electrons is expressed in terms of
spin-flip probabilities, which on their part are put down to the exactly known
dynamic quantities of the system.
The calculated electron spin polarization shows remarkable dependencies on
the electron velocity perpendicular to the emitting plane and the strength of
s-f coupling. Experimentally observed polarization values of about 90% are well
understood within the framework of the proposed model.Comment: accepted (Physical Review B); 10 pages, 11 figures;
http://orion.physik.hu-berlin.de
Perfect imaging with positive refraction in three dimensions
Maxwell's fish eye has been known to be a perfect lens within the validity
range of ray optics since 1854. Solving Maxwell's equations we show that the
fish-eye lens in three dimensions has unlimited resolution for electromagnetic
waves
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