1,885 research outputs found
Polaritonic states in a dielectric nanoguide: localization and strong coupling
Propagation of light through dielectrics lies at the heart of optics.
However, this ubiquitous process is commonly described using phenomenological
dielectric function and magnetic permeability , i.e. without
addressing the quantum graininess of the dielectric matter. Here, we present a
theoretical study where we consider a one-dimensional ensemble of atoms in a
subwavelength waveguide (nanoguide) as fundamental building blocks of a model
dielectric. By exploring the roles of the atom-waveguide coupling efficiency,
density, disorder, and dephasing, we establish connections among various
features of polaritonic light-matter states such as localization, super and
subradiance, and strong coupling. In particular, we show that coherent multiple
scattering of light among atoms that are coupled via a single propagating mode
can gives rise to Rabi splitting. These results provide important insight into
the underlying physics of strong coupling reported by recent room-temperature
experiments with microcavities and surface plasmons.Comment: 10 pages, 6 figure
Twisting and tweezing the spin wave: on vortices, skyrmions, helical waves, and the magnonic spiral phase plate
Spin waves are the low-energy excitations of magnetically ordered materials.
They are key elements in the stability analysis of the ordered phase and have a
wealth of technological applications. Recently, we showed that spin waves of a
magnetic nanowire may carry a definite amount of orbital angular momentum
components along the propagation direction. This helical, in addition to the
chiral, character of the spin waves is related to the spatial modulations of
the spin wave phase across the wire. It, however, remains a challenge to
generate and control such modes with conventional magnetic fields. Here, we
make the first proposal for a \textit{magnetic} spiral phase plate by
appropriately synthesizing two magnetic materials that have different speeds of
spin waves. It is demonstrated with full-numerical micromagnetic simulations
that despite the complicated structure of demagnetization fields, a homogeneous
spin wave passing through the spiral phase plate attains the required twist and
propagates further with the desired orbital angular momentum. While excitations
from the ordered phase may have a twist, the magnetization itself can be
twisted due to internal fields and forms what is known as a magnetic vortex. We
point out the differences between both types of magnetic phenomena and discuss
their possible interaction.Comment: 6 pages, 5 figure
The Buffered Block Forward Backward technique for solving electromagnetic wave scattering problems
This work focuses on efficient numerical techniques for solving electromagnetic wave
scattering problems. The research is focused on three main areas: scattering from perfect
electric conductors, 2D dielectric scatterers and 3D dielectric scattering objects. The
problem of fields scattered from perfect electric conductors is formulated using the Electric
Field Integral Equation. The Coupled Field Integral Equation is used when a 2D homogeneous
dielectric object is considered. The Combined Field Integral Equation describes the
problem of scattering from 3D homogeneous dielectric objects. Discretising the Integral
Equation Formulation using the Method of Moments creates the matrix equation that is
to be solved. Due to the large number of discretisations necessary the resulting matrices
are of significant size and therefore the matrix equations cannot be solved by direct inversion
and iterative methods are employed instead. Various iterative techniques for solving
the matrix equation are presented including stationary methods such as the ”forwardbackward”
technique, as well its matrix-block version. A novel iterative solver referred to
as Buffered Block Forward Backward (BBFB) method is then described and investigated.
It is shown that the incorporation of buffer regions dampens spurious diffraction effects
and increases the computational efficiency of the algorithm. The BBFB is applied to both
perfect electric conductors and homogeneous dielectric objects. The convergence of the
BBFB method is compared to that of other techniques and it is shown that, depending on
the grouping and buffering used, it can be more effective than classical methods based on
Krylov subspaces for example. A possible application of the BBFB, namely the design of
2D dielectric photonic band-gap TeraHertz waveguides is investigated.
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