338 research outputs found
Broadband suppression of backscattering at optical frequencies using low permittivity dielectric spheres
The exact suppression of backscattering from rotationally symmetric objects
requires dual symmetric materials where . This prevents
their design at many frequency bands, including the optical one, because
magnetic materials are not available. Electromagnetically small non-magnetic
spheres of large permittivity offer an alternative. They can be tailored to
exhibit balanced electric and magnetic dipole polarizabilities, which result in
approximate zero backscattering. In this case, the effect is inherently
narrowband. Here, we put forward a different alternative that allows broadband
functionality: Electromagnetically large spheres made from low permittivity
materials. The effect occurs in a parameter regime that approaches the trivial
case, where approximate duality is met in a
weakly wavelength dependence fashion. Despite the low permittivity, the overall
scattering response of the spheres is still significant. Radiation patterns
from these spheres are shown to be highly directive across an octave spanning
band. The effect is analytically and numerically shown using the Mie
coefficients.Comment: 6 Figure
Optical alignment of oval graphene flakes
Patterned graphene, as an atomically thin layer, supports localized surface
plasmon-polaritons (LSPPs) at mid-infrared or far-infrared frequencies. This
provides a pronounced optical force/torque in addition to large optical cross
sections and will make it an ideal candidate for optical manipulation. Here, we
study the optical force and torque exerted by a linearly polarized plane wave
on circular and oval graphene flakes. Whereas the torque vanishes for circular
flakes, the finite torque allows rotating and orienting oval flakes relative to
the electric field polarization. Depending on the wavelength, the alignment is
either perpendicular or parallel. In our contribution, we rely on full-wave
numerical simulation but also on an analytical model that treats the graphene
flakes in dipole approximation. The presented results reveal a good level of
control on the spatial alignment of graphene flakes subjected to far-infrared
illumination.Comment: Copyright 2016 Optical Society of America. One print or electronic
copy may be made for personal use only. Systematic reproduction and
distribution, duplication of any material in this paper for a fee or for
commercial purposes, or modifications of the content of this paper are
prohibited. Online abstract lin
Asymmetric transmission of linearly polarized light at optical metamaterials
We experimentally demonstrate a three-dimensional chiral optical metamaterial
that exhibits an asymmetric transmission for forwardly and backwardly
propagating linearly polarized light. The observation of this novel effect
requires a metamaterial composed of three-dimensional chiral metaatoms without
any rotational symmetry. Our analysis is supported by a systematic
investigation of the transmission matrices for arbitrarily complex, lossy media
that allows deriving a simple criterion for asymmetric transmission in an
arbitrary polarization base. Contrary to physical intuition, in general the
polarization eigenstates in such three-dimensional and low-symmetry
metamaterials do not obey fxed relations and the associated transmission
matrices cannot be symmetrized
Tunable Graphene Antennas for Selective Enhancement of THz-Emission
In this paper, we will introduce THz graphene antennas that strongly enhance
the emission rate of quantum systems at specific frequencies. The tunability of
these antennas can be used to selectively enhance individual spectral features.
We will show as an example that any weak transition in the spectrum of coronene
can become the dominant contribution. This selective and tunable enhancement
establishes a new class of graphene-based THz devices, which will find
applications in sensors, novel light sources, spectroscopy, and quantum
communication devices
A 3D tunable and multi-frequency graphene plasmonic cloak
We demonstrate the possibility of cloaking three-dimensional objects at multi-frequencies in the far-infrared part of the spectrum. The proposed cloaking mechanism exploits graphene layers wrapped around the object to be concealed. Graphene layers are doped via a variable external voltage difference permitting continuous tuning of the cloaking frequencies. Particularly, two configurations are investigated: (i) Only one graphene layer is used to suppress the scattering from a dielectric sphere. (ii) Several of these layers biased at different gate voltages are used to achieve a multifrequency cloak. These frequencies can be set independently. The proposed cloak’s functionality is verified by near- and far-field computations. By considering geometry and material parameters that are realizable by practical experiments, we contribute to the development of graphene based plasmonic applications that may find use in disruptive photonic technologies
Perfect absorbers on curved surfaces and their potential applications
Recently perfect metamaterial absorbers triggered some fascination since they permit the observation of an extreme interaction of light with a nanostructured thin film. For the first time we evaluate here the functionality of such perfect absorbers if they are applied on curved surfaces. We probe their optical response and discuss potential novel applications. Examples are the complete suppression of back-scattered light from the covered objects, rendering it cloaked in reflection, and their action as optical black holes
Decomposing the scattered field of two-dimensional metaatoms into multipole contributions
We introduce a technique to decompose the scattered near field of
two-dimensional arbitrary metaatoms into its multipole contributions. To this
end we expand the scattered field upon plane wave illumination into cylindrical
harmonics as known from Mie theory. By relating these cylin- drical harmonics
to the field radiated by Cartesian multipoles, the contribution of the lowest
order electric and magnetic multipoles can be identified. Revealing these
multipoles is essential for the design of metamaterials because they largely
determine the character of light propagation. In par- ticular, having this
information at hand it is straightforward to distinguish between effects that
result either from the arrangement of the metaatoms or from their particular
design
- …