826 research outputs found
Enhanced transmission of slit arrays in an extremely thin metallic film
Horizontal resonances of slit arrays are studied. They can lead to an
enhanced transmission that cannot be explained using the single-mode
approximation. A new type of cavity resonance is found when the slits are
narrow for a wavelength very close to the period. It can be excited for very
low thicknesses. Optimization shows these structures could constitute
interesting monochromatic filters
Theory of fishnet negative-index optical metamaterials
We theoretically study fishnet metamaterials at optical frequencies. In
contrast to earlier works, we provide a microscopic description by tracking the
transversal and longitudinal flows of energy through the fishnet mesh composed
of intersecting subwavelength plasmonic waveguides. The analysis is supported
by a semi-analytical model based on surface-plasmon coupled-mode equations,
which provides accurate formulas for the fishnet refractive index, including
the real-negative and imaginary parts. The model simply explains how the
surface plasmons couple at the waveguide intersections and it shines new light
on the fishnet negative-index paradigm at optical frequencies. Extension of the
theory for loss-compensated metamaterials with gain media is also presented.Comment: 4 figure
On the attenuation coefficient of monomode periodic waveguides
It is widely accepted that, on ensemble average, the transmission T of guided
modes decays exponentially with the waveguide length L due to small
imperfections, leading to the important figure of merit defined as the
attenuation-rate coefficient alpha = -/L. In this letter, we evidence
that the exponential-damping law is not valid in general for periodic monomode
waveguides, especially as the group velocity decreases. This result that
contradicts common beliefs and experimental practices aiming at measuring alpha
is supported by a theoretical study of light transport in the limit of very
small imperfections, and by numerical results obtained for two waveguide
geometries that offer contrasted damping behaviours
Slow-wave effect and mode-profile matching in Photonic Crystal microcavities
Physical mechanisms involved in the light confinement in photonic crystal
slab microcavities are investigated. We first present a full three-dimensional
numerical study of these microcavities. Then, to gain physical insight into the
confinement mechanisms, we develop a Fabry-Perot model. This model provides
accurate predictions and sheds new light on the physics of light confinement.
We clearly identify two mechanisms to enhance the Q factor of these
microcavities. The first one consists in improving the mode-profile matching at
the cavity terminations and the second one in using a slow wave in the cavity.Comment: accepted for publication in Phys. Rev. B, 8 pages, 4 figure
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
Sharing the fruits of growth from 1950 to 2008: A surplus-accounting approach
In this paper, we apply the surplus accounting methodology to analyze the distribution of the fruits of growth between production factors over the period 1950-2008. Three production factors are distinguished: paid employment, self-employment and capital. The surplus distributed to capital is nil on average. The employees received a surplus linked to the evolution of total factor productivity, which experienced a slowdown in the 1980s Since 2007, the distributed surplus has sharply dropped, due to an increase in external deduction. The evolution of the surplus is, then, confronted to value-added distribution, by focusing on the capital-labour substitution in the 1980s. The standard framework of surplus accounting is, finally, extended by taking the Welfare System and its financing into account. Indeed, even if the Welfare System is mostly financed by social contributions paid by production factors, social benefits are also distributed to agents who are not involved in the production process, namely the pensioners, the unemployed, and the non-working population. We find that the surplus distributed to employees is lower when social contributions are taken into account. In the meantime, a half-percentage point of the value-added growth rate is assigned each year to the financing of the old-age insurance, whose main part however (0.4 point) accrues tothe growing number of new pensioners. Nevertheless, the incomes after social benefits allocated to the employed, the unemployed, and pensioners grow at a similar pace.Surplus Accounting, Value-Added Distribution, Welfare System, Pensioners
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