247 research outputs found
Calculation of material properties and ray tracing in transformation media
Complex and interesting electromagnetic behavior can be found in spaces with
non-flat topology. When considering the properties of an electromagnetic medium
under an arbitrary coordinate transformation an alternative interpretation
presents itself. The transformed material property tensors may be interpreted
as a different set of material properties in a flat, Cartesian space. We
describe the calculation of these material properties for coordinate
transformations that describe spaces with spherical or cylindrical holes in
them. The resulting material properties can then implement invisibility cloaks
in flat space. We also describe a method for performing geometric ray tracing
in these materials which are both inhomogeneous and anisotropic in their
electric permittivity and magnetic permeability
Focussing Light Using Negative Refraction
A slab of negatively refracting material, thickness d, can focus an image at
a distance 2d from the object. The negative slab cancels an equal thickness of
positive space. This result is a special case of a much wider class of
focussing: any medium can be optically cancelled by an equal thickness of
material constructed to be an inverted mirror image of the medium, with,
and reversed in sign. We introduce the powerful technique of
coordinate transformation, mapping a known system into an equivalent system, to
extend the result to a much wider class of structures including cylinders,
spheres, and intersecting planes and hence show how to produce magnified
images. All the images are perfect in the sense that both the near and far
fields are brought to a focus and hence reveal sub wavelength details.Comment: pdf file onl
Determination of Effective Permittivity and Permeability of Metamaterials from Reflection and Transmission Coefficients
We analyze the reflection and transmission coefficients calculated from
transfer matrix simulations on finite lenghts of electromagnetic metamaterials,
to determine the effective permittivity and permeability. We perform this
analysis on structures composed of periodic arrangements of wires, split ring
resonators (SRRs) and both wires and SRRs. We find the recovered
frequency-dependent permittivity and permeability are entirely consistent with
analytic expressions predicted by effective medium arguments. Of particular
relevance are that a wire medium exhibits a frequency region in which the real
part of permittivity is negative, and SRRs produce a frequency region in which
the real part of permeability is negative. In the combination structure, at
frequencies where both the recovered real part of permittivity and permeability
are simultaneously negative, the real part of the index-of-refraction is found
also to be unambigously negative.Comment: *.pdf file, 5 figure
Ray-optical refraction with confocal lenslet arrays
Two parallel lenslet arrays with focal lengths f1 and f2 that share a common focal plane (that is, which are separated by a distance f1+f2) can refract transmitted light rays according to Snell's law, but with the 'sin's replaced with 'tan's. This is the case for a limited range of input angles and other conditions. Such confocal lenslet arrays can therefore simulate the interface between optical media with different refractive indices, n1 and n2, whereby the ratio η=-f2/f1 plays the role of the refractive-index ratio n2/n1. Suitable choices of focal lengths enable positive and negative refraction. In contrast to Snell's law, which leads to nontrivial geometric imaging by a planar refractive-index interface only for the special case of n1=±n2, the modified refraction law leads to geometric imaging by planar confocal lenslet arrays for any value of η. We illustrate some of the properties of confocal lenslet arrays with images rendered using ray-tracing software
Anisotropy and oblique total transmission at a planar negative-index interface
We show that a class of negative index (n) materials has interesting
anisotropic optical properties, manifest in the effective refraction index that
can be positive, negative, or purely imaginary under different incidence
conditions. With dispersion taken into account, reflection at a planar
negative-index interface exhibits frequency selective total oblique
transmission that is distinct from the Brewster effect.
Finite-difference-time-domain simulation of realistic negative-n structures
confirms the analytic results based on effective indices.Comment: to appear in Phys. Rev.
Impact of the inherent periodic structure on the effective medium description of left-handed and related meta-materials
We study the frequency dependence of the effective electromagnetic parameters
of left-handed and related meta-materials of the split ring resonator and wire
type. We show that the reduced translational symmetry (periodic structure)
inherent to these meta-materials influences their effective electromagnetic
response. To anticipate this periodicity, we formulate a periodic effective
medium model which enables us to distinguish the resonant behavior of
electromagnetic parameters from effects of the periodicity of the structure. We
use this model for the analysis of numerical data for the transmission and
reflection of periodic arrays of split ring resonators, thin metallic wires,
cut wires as well as the left-handed structures. The present method enables us
to identify the origin of the previously observed resonance/anti-resonance
coupling as well as the occurrence of negative imaginary parts in the effective
permittivities and permeabilities of those materials. Our analysis shows that
the periodicity of the structure can be neglected only for the wavelength of
the electromagnetic wave larger than 30 space periods of the investigated
structure.Comment: 23 pages, 14 figure
Limitations on Sub-Diffraction Imaging with a Negative Refractive Index Slab
Recently it has been proposed that a planar slab of material, for which both
the permittivity and permeability have the values of -1, could bring not only
the propagating fields associated with a source to a focus, but could also
refocus the nonpropagating near-fields, thereby achieving a subdiffraction
image. In this work we discuss the sensitivity of the subwavelength focus to
various slab parameters, pointing out the connection to slab plasmon modes. We
also note and resolve a paradox associated with the perfect imaging of a point
source. We conclude that subwavelength resolution is achievable with available
technology, but only by implementation of a critical set of design parameters.Comment: pdf fil
Negative refraction and left-handed behavior in two-dimensional photonic crystals
We systematically examine the conditions of obtaining left-handed (LH)
behavior in photonic crystals. Detailed studies of the phase and group
velocities as well as the phase np and group ng refractive index are given. The
existence of negative refraction does not guarantee the existence of negative
index of refraction and so LH behavior. A wedge type of experiment is suggested
that can unambiguously distiguinsh between cases of negative refraction that
occur when left-handed behavior is present, from cases that show negative
refraction without LH behavior.Comment: 4 pages 4 figures, submitted to Phys. Rev. B Rapid Communication
Optomagnetic composite medium with conducting nanoelements
A new type of metal-dielectric composites has been proposed that is
characterised by a resonance-like behaviour of the effective permeability in
the infrared and visible spectral ranges. This material can be referred to as
optomagnetic medium. The analytical formalism developed is based on solving the
scattering problem for considered inclusions with impedance boundary condition,
which yields the current and charge distributions within the inclusions. The
presence of the effective magnetic permeability and its resonant properties
lead to novel optical effects and open new possible applications.Comment: 48 pages, 13 figures. accepted to Phys. Rev. B; to appear vol. 66,
200
The Quantum-Mechanical Position Operator in Extended Systems
The position operator (defined within the Schroedinger representation in the
standard way) becomes meaningless when periodic boundary conditions are adopted
for the wavefunction, as usual in condensed matter physics. We show how to
define the position expectation value by means of a simple many-body operator
acting on the wavefunction of the extended system. The relationships of the
present findings to the Berry-phase theory of polarization are discussed.Comment: Four pages in RevTe
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