15,949 research outputs found
Surface-Wave Dispersion Retrieval Method and Synthesis Technique for Bianisotropic Metasurfaces
We propose a surface-wave dispersion retrieval method and synthesis technique
that applies to bianisotropic metasurfaces that are embedded in symmetric or
asymmetric environments. Specifically, we use general zero-thickness sheet
transition conditions to relate the propagation constants of surface-wave modes
to the bianisotropic susceptibility components of the metasurface, which can
themselves be directly related to its scattering parameters. It is then
possible to either obtain the metasurface dispersion diagram from its known
susceptibilities or, alternatively, compute the susceptibilities required to
achieve a desired surface-wave propagation. The validity of the method is
demonstrated by comparing its results to those obtained with exact dispersion
relations of well known structures such as the propagation of surface plasmons
on thin metallic films. In particular, this work reveals that it is possible to
achieve surface-wave propagation only on one side of the metasurface either by
superposition of symmetric and asymmetric modes in the case of anisotropic
metasurfaces or by completely forbidding the existence of the surface wave on
one side of the structure using bianisotropic metasurfaces
Ab initio theory of Fano resonances in plasmonic nanostructures and metamaterials
An ab initio theory for Fano resonances in plasmonic nanostructures and
metamaterials is developed using Feshbach formalism. It reveals the role played
by the electromagnetic modes and material losses in the system, and enables the
engineering of Fano resonances in arbitrary geometries. A general formula for
the asymmetric resonance in a non-conservative system is derived. The influence
of the electromagnetic interactions on the resonance line shape is discussed
and it is shown that intrinsic losses drive the resonance contrast, while its
width is mostly determined by the coupling strength between the non-radiative
mode and the continuum. The analytical model is in perfect agreement with
numerical simulations.Comment: 13 pages, 5 figure
Multipolar Origin of the Unexpected Transverse Force Resulting from Two-Wave Interference
We propose a theoretical study on the electromagnetic forces resulting from
the superposition of a TE and TM plane waves interacting with a sphere.
Specifically, we first show that, under such an illumination condition, the
sphere is subjected to a force transverse to the propagation direction of the
waves. We then analyze the physical origin of this counter-intuitive behavior
using a multipolar decomposition of the electromagnetic modes involved in that
scattering process. This analysis reveals that interference effects, due to the
two-wave illumination, lead to a Kerker-like asymmetric scattering behavior
resulting in this peculiar transverse force
Random mixtures of polycyclic aromatic hydrocarbon spectra match interstellar infrared emission
The mid-infrared (IR; 5-15~m) spectrum of a wide variety of astronomical
objects exhibits a set of broad emission features at 6.2, 7.7, 8.6, 11.3 and
12.7 m. About 30 years ago it was proposed that these signatures are due
to emission from a family of UV heated nanometer-sized carbonaceous molecules
known as polycyclic aromatic hydrocarbons (PAHs), causing them to be referred
to as aromatic IR bands (AIBs). Today, the acceptance of the PAH model is far
from settled, as the identification of a single PAH in space has not yet been
successful and physically relevant theoretical models involving ``true'' PAH
cross sections do not reproduce the AIBs in detail. In this paper, we use the
NASA Ames PAH IR Spectroscopic Database, which contains over 500
quantum-computed spectra, in conjunction with a simple emission model, to show
that the spectrum produced by any random mixture of at least 30 PAHs converges
to the same 'kernel'-spectrum. This kernel-spectrum captures the essence of the
PAH emission spectrum and is highly correlated with observations of AIBs,
strongly supporting PAHs as their source. Also, the fact that a large number of
molecules are required implies that spectroscopic signatures of the individual
PAHs contributing to the AIBs spanning the visible, near-infrared, and far
infrared spectral regions are weak, explaining why they have not yet been
detected. An improved effort, joining laboratory, theoretical, and
observational studies of the PAH emission process, will support the use of PAH
features as a probe of physical and chemical conditions in the nearby and
distant Universe
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