1,091 research outputs found
Ultrafast nonlinear dynamics of thin gold films due to an intrinsic delayed nonlinearity
Using long-range surface plasmon polaritons light can propagate in metal
nano-scale waveguides for ultracompact opto-electronic devices. Gold is an
important material for plasmonic waveguides, but although its linear optical
properties are fairly well understood, the nonlinear response is still under
investigation. We consider propagation of pulses in ultrathin gold strip
waveguides, modeled by the nonlinear Schr\"odinger equation. The nonlinear
response of gold is accounted for by the two-temperature model, revealing it as
a delayed nonlinearity intrinsic in gold. The consequence is that the measured
nonlinearities are strongly dependent on pulse duration. This issue has so far
only been addressed phenomenologically, but we provide an accurate estimate of
the quantitative connection as well as a phenomenological theory to understand
the enhanced nonlinear response as the gold thickness is reduced. In comparison
with the previous works, the analytical model for the power-loss equation has
been improved, and can be applied now to cases with a high laser peak power. We
show new fits to experimental data from literature and provide updated values
for the real and imaginary part of the nonlinear susceptibility of gold for
various pulse durations and gold layer thicknesses. Our simulations show that
the nonlinear loss is inhibiting efficient nonlinear interaction with low-power
laser pulses. We therefore propose to design waveguides suitable for the
mid-IR, where the ponderomotive instantaneous nonlinearity can dominate over
the delayed hot-electron nonlinearity and provide a suitable plasmonics
platform for efficient ultrafast nonlinear optics.Comment: J. Opt., in pres
Epsilon-Near-Zero Grids for On-chip Quantum Networks
Realization of an on-chip quantum network is a major goal in the field of
integrated quantum photonics. A typical network scalable on-chip demands
optical integration of single photon sources, optical circuitry and detectors
for routing and processing of quantum information. Current solutions either
notoriously experience considerable decoherence or suffer from extended
footprint dimensions limiting their on-chip scaling. Here we propose and
numerically demonstrate a robust on-chip quantum network based on an
epsilon-near-zero (ENZ) material, whose dielectric function has the real part
close to zero. We show that ENZ materials strongly protect quantum information
against decoherence and losses during its propagation in the dense network. As
an example, we model a feasible implementation of an ENZ network and
demonstrate that quantum information can be reliably sent across a titanium
nitride grid with a coherence length of 434 nm, operating at room temperature,
which is more than 40 times larger than state-of-the-art plasmonic analogs. Our
results facilitate practical realization of large multi-node quantum photonic
networks and circuits on-a-chip.Comment: 13 pages, 5 figure
Refraction enhancement in plasmonics by the coherent control of plasmon resonances
A plasmonic nanoantenna probed by a plane-polarized optical field in a medium
with no gain materials can show zero absorption or even amplification, while
exhibiting maximal polarizability. This occurs through coupling to an adjacent
nanoantenna in a specially designed metamolecule, which is pumped by an
orthogonal optical field with phase shift. The introduced scheme is a classical
counterpart of an effect known in quantum optics as enhancement of the index of
refraction (EIR). In contrary to electromagnetically induced transparency
(EIT), where the medium is rendered highly dispersive at the point of zero
susceptibility and minimum absorption, in the EIR the system exhibits large
susceptibility and low dispersion at the point of zero or negative absorption.
The plasmonic analogue of the EIR allows for coherent control over the
polarizability and absorption of plasmonic nanoantennas, offering a novel
approach to all optical switching and coherent control of transmission,
diffraction and polarization conversion properties of plasmonic nanostructures,
as well as propagation properties of surface plasmon polaritons on
metasurfaces. It may also open up the way for lossless or amplifying
propagation of optical waves in zero-index to high refractive index plasmonic
metamaterial
Applicability of point dipoles approximation to all-dielectric metamaterials
All-dielectric metamaterials consisting of high-dielectric inclusions in a
low-dielectric matrix are considered as a low-loss alternative to resonant
metal-based metamaterials. In this contribution we investigate the
applicability of the point electric and magnetic dipoles approximation to
dielectric meta-atoms on the example of a dielectric ring metamaterial. Despite
the large electrical size of high-dielectric meta-atoms, the dipole
approximation allows for accurate prediction of the metamaterials properties
for the rings with diameters up to ~0.8 of the lattice constant. The results
provide important guidelines for design and optimization of all-dielectric
metamaterials.Comment: 10 pages, 5 fugures, submitted to Physical Review
Dark-field hyperlens: Super-resolution imaging of weakly scattering objects
We propose and numerically demonstrate a technique for subwavelength imaging
based on a metal-dielectric multilayer hyperlens designed in such a way that
only the large-wavevector waves are transmitted while all propagating waves
from the image area are blocked by the hyperlens. As a result, the image plane
only contains scattered light from subwavelength features of the objects and is
free from background illumination. Similar in spirit to conventional dark-field
microscopy, the proposed dark-field hyperlens is promising for optical imaging
of weakly scattering subwavelength objects, such as optical nanoscopy of
label-free biological objects.Comment: 6 figure
Regulation of family reunification in the EU : Shaping the profile of Finland
This thesis touches upon the subject of family reunification, being highly problematised and politicised in the context of the EU member states. Demonisation of the matter, largely stems from the fact that reunification based on family ties is the main mode of entry onto the territory of the EU available for third country nationals. Intensified further in the context of the erupted European refugee crisis, family reunification is viewed by many EU member states as an area to create ever further restrictive regulations. The thesis explores how regulation over family reunification is currently being executed in the EU, and how nation states participate in its management. The work identifies that procedural sides of family reunification have further consequences for members of a reunited family, such as development of dependancy. Furthermore, the Finnish family migration legislation is being examined from the perspective of possible âwindow of opportunityâ for deepening restrictions, implied by the present political discourse within the country
From Topology to Generalised Dimensional Reduction
In the usual procedure for toroidal Kaluza-Klein reduction, all the
higher-dimensional fields are taken to be independent of the coordinates on the
internal space. It has recently been observed that a generalisation of this
procedure is possible, which gives rise to lower-dimensional ``massive''
supergravities. The generalised reduction involves allowing gauge potentials in
the higher dimension to have an additional linear dependence on the toroidal
coordinates. In this paper, we show that a much wider class of generalised
reductions is possible, in which higher-dimensional potentials have additional
terms involving differential forms on the internal manifold whose exterior
derivatives yield representatives of certain of its cohomology classes. We
consider various examples, including the generalised reduction of M-theory and
type II strings on K3, Calabi-Yau and 7-dimensional Joyce manifolds. The
resulting massive supergravities support domain-wall solutions that arise by
the vertical dimensional reduction of higher-dimensional solitonic p-branes and
intersecting p-branes.Comment: Latex, 24 pages, no figures, typo corrected, reference added and
discussion of duality extende
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