3,826 research outputs found
Bandwidth control of forbidden transmission gaps in compound structures with subwavelength slits
Phase resonances in transmission compound structures with subwavelength slits
produce sharp dips in the transmission response. For all equal slits, the
wavelengths of these sharp transmission minima can be varied by changing the
width or the length of all the slits. In this paper we show that the width of
the dip, i.e., the frequency range of minimum transmittance, can be controlled
by making at least one slit different from the rest within a compound unit
cell. In particular, we investigate the effect that a change in the dielectric
filling, or in the length of a single slit produces in the transmission
response. We also analyze the scan angle behavior of these structures by means
of band diagrams, and compare them with previous results for all-equal slit
structures.Comment: 16 pages, 5 figures, submitted to Phys. Rev.
Fundamental mechanism underlying subwavelength optics of metamaterials: Charge oscillation-induced light emission and interference
Interactions between light and conducting nanostructures can result in a
variety of novel and fascinating phenomena. These properties may have wide
applications, but their underlying mechanisms have not been completely
understood. From calculations of surface charge density waves on conducting
gratings and by comparing them with classical surface plasmons, we revealed a
general yet concrete picture about coupling of light to free electron
oscillation on structured conducting surfaces that can lead to oscillating
subwavelength charge patterns (i.e., spoof surface plasmons but without the
dispersion property of classical surface plasmons). New wavelets emitted from
these light sources then destructively interfere to form evanescent waves. This
principle, usually combined with other mechanisms (e.g. resonance), is mainly a
geometrical effect that can be universally involved in light scattering from
all periodic and nonperiodic structures containing free electrons, including
perfect conductors. The spoof surface plasmon picture may provide clear
guidelines for developing metamaterial-based nano-optical devices.Comment: 11 pages, 9 figures, submitted to PRB (2009
Hyper-Raman scattering analysis of the vibrations in vitreous boron oxide
Hyper-Raman scattering has been measured on vitreous boron oxide,
BO. This spectroscopy, complemented with Raman scattering and
infrared absorption, reveals the full set of vibrations that can be observed
with light. A mode analysis is performed based on the local D symmetry
of BO triangles and BO boroxol rings. The results show that in
BO the main spectral components can be succesfully assigned using
this relatively simple model. In particular, it can be shown that the
hyper-Raman boson peak arises from external modes that correspond mainly to
librational motions of rigid boroxol rings.Comment: 13 pages, 11 figures, 2 table
Optimal light harvesting structures at optical and infrared frequencies
One-dimensional light harvesting structures with a realistic geometry
nano-patterned on an opaque metallic film are optimized to render high
transmission efficiencies at optical and infrared frequencies. Simple design
rules are developed for the particular case of a slit-groove array with a given
number of grooves that are symmetrically distributed with respect to a central
slit. These rules take advantage of the hybridization of Fabry-Perot modes in
the slit and surface modes of the corrugated metal surface. Same design rules
apply for optical and infrared frequencies. The parameter space of the groove
array is also examined with a conjugate gradient optimization algorithm that
used as a seed the geometries optimized following physical intuition. Both
uniform and nonuniform groove arrays are considered. The largest transmission
enhancement, with respect to a uniform array, is obtained for a chirped groove
profile. Such enhancement is a function of the wavelength. It decreases from
39% in the optical part of the spectrum to 15% at the long wavelength infrared.Comment: 13 pages, 5 figure
Enhanced transmission versus localization of a light pulse by a subwavelength metal slit: Can the pulse have both characteristics?
The existence of resonant enhanced transmission and collimation of light
waves by subwavelength slits in metal films [for example, see T.W. Ebbesen et
al., Nature (London) 391, 667 (1998) and H.J. Lezec et al., Science, 297, 820
(2002)] leads to the basic question: Can a light be enhanced and simultaneously
localized in space and time by a subwavelength slit? To address this question,
the spatial distribution of the energy flux of an ultrashort (femtosecond)
wave-packet diffracted by a subwavelength (nanometer-size) slit was analyzed by
using the conventional approach based on the Neerhoff and Mur solution of
Maxwell's equations. The results show that a light can be enhanced by orders of
magnitude and simultaneously localized in the near-field diffraction zone at
the nm- and fs-scales. Possible applications in nanophotonics are discussed.Comment: 5 figure
Broadband Extraordinary Transmission in a Single Sub-wavelength Aperture
Coordinate transformation is applied to design an all-dielectric device for
Extraordinary Transmission (ET) in a single sub-wavelength slit. The proposed
device has a broadband feature and can be applied from microwave to visible
frequency bands. Finite-Difference Time-Domain (FDTD) simulations are used to
verify the device's performance. The results show that significantly increased
transmission is achieved through the sub-wavelength aperture from 4 GHz to 8
GHz when the device is applied. In contrast with previously reported systems,
the frequency sensitivity of the new device is very low.Comment: 9 pages, 8 figure
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