114 research outputs found
Surface plasmon resonance under conditions of electromagnetically induced transparency
A scheme for a surface plasmon resonance system under conditions of
electromagnetically induced transparency (EIT) is proposed. The system is
composed of three layers: a prism, a thin metal film, and a hybrid dielectric
consisting of EIT atoms and a background substance. A probe and a coupling
laser beam are input. Corresponding analytical formulas are derived for the
cases when one or both of the laser beams excite surface plasmon polaritons at
the metal/dielectric interface. Under resonance conditions, an extremely sharp
dip appears in the reflectivity-frequency spectrum of the probe field,
revealing new properties of two-dimensional EIT. The reflectivity is extremely
sensitive to shifts in the laser frequencies and atomic levels, and to
variations of permittivity of the substrate. This EIT-SPR system may to be used
for novel magnetometers and biosensors
Tuning the polarization states of optical spots at the nanoscale on the poincar´e sphere using a plasmonic nanoantenna
It is shown that the polarization states of optical spots at the nanoscale can be manipulated to various points on the Poincar´e sphere using a plasmonic nanoantenna. Linearly, circularly, and elliptically polarized near-field optical spots at the nanoscale are achieved with various polarization states on the Poincar´e sphere using a plasmonic nanoantenna. A novel plasmonic nanoantenna is illuminated with diffraction-limited linearly polarized light. It is demonstrated
that the plasmonic resonances of perpendicular and longitudinal components of the nanoantenna and the angle of incident polarization can be tuned to obtain optical spots beyond the diffraction limit with a desired polarization and handedness
Modelling of photonic wire Bragg Gratings
Some important properties of photonic wire Bragg grating structures have been investigate. The design, obtained as a generalisation of the full-width gap grating, has been modelled using 3D finite-difference time-domain simulations. Different types of stop-band have been observed. The impact of the grating geometry on the lowest order (longest wavelength) stop-band has been investigated - and has identified deeply indented configurations where reduction of the stop-bandwidth and of the reflectivity occurred. Our computational results have been substantially validated by an experimental demonstration of the fundamental stop-band of photonic wire Bragg gratings fabricated on silicon-on-insulator material. The accuracy of two distinct 2D computational models based on the effective index method has also been studied - because of their inherently much greater rapidity and consequent utility for approximate initial designs. A 2D plan-view model has been found to reproduce a large part of the essential features of the spectral response of full 3D models
Ultrahigh field electron cyclotron resonance absorption in InMnAs films
We have carried out an ultrahigh field cyclotron resonance study of -type
InMnAs films, with Mn composition ranging from 0 to 12%, grown
on GaAs by low temperature molecular beam epitaxy. We observe that the electron
cyclotron resonance peak shifts to lower field with increasing . A detailed
comparison of experimental results with calculations based on a modified
Pidgeon-Brown model allows us to estimate the {\em s-d} and {\em p-d} exchange
coupling constants, and , for this important III-V dilute
magnetic semiconductor system.Comment: 4 pages, 4 figure
Near-field optical power transmission of dipole nano-antennas
Nano-antennas in functional plasmonic applications require high near-field optical power transmission. In this study, a model is developed to compute the near-field optical power transmission in the vicinity of a nano-antenna.
To increase the near-field optical power transmission from a nano-antenna, a tightly focused beam of light is utilized to illuminate a metallic nano-antenna. The modeling and simulation of these structures is performed using 3-D finite element method based full-wave solutions of Maxwell’s equations. Using the optical power transmission model, the interaction of a focused beam of light with plasmonic nanoantennas is investigated. In addition, the tightly focused beam of light is passed through a band-pass filter to identify the effect of various regions of the angular spectrum to the near-field radiation of a dipole nano-antenna. An extensive parametric study is performed to quantify the effects of various parameters on the transmission efficiency of dipole nano-antennas, including length, thickness, width, and the composition of the antenna, as well as the wavelength and half-beam angle of incident light. An optimal dipole nanoantenna geometry is identified based on the parameter studies in this work. In addition, the results of this study show the interaction of the optimized dipole nano-antenna with a magnetic recording medium when it is illuminated with a focused beam of light
Plasmonic excitations in noble metals: The case of Ag
The delicate interplay between plasmonic excitations and interband
transitions in noble metals is described by means of {\it ab initio}
calculations and a simple model in which the conduction electron plasmon is
coupled to the continuum of electron-hole pairs. Band structure effects,
specially the energy at which the excitation of the -like bands takes place,
determine the existence of a subthreshold plasmonic mode, which manifests
itself in Ag as a sharp resonance at 3.8 eV. However, such a resonance is not
observed in the other noble metals. Here, this different behavior is also
analyzed and an explanation is provided.Comment: 9 pages, 8 figure
Thermal correction to the Casimir force, radiative heat transfer, and an experiment
The low-temperature asymptotic expressions for the Casimir interaction
between two real metals described by Leontovich surface impedance are obtained
in the framework of thermal quantum field theory. It is shown that the Casimir
entropy computed using the impedance of infrared optics vanishes in the limit
of zero temperature. By contrast, the Casimir entropy computed using the
impedance of the Drude model attains at zero temperature a positive value which
depends on the parameters of a system, i.e., the Nernst heat theorem is
violated. Thus, the impedance of infrared optics withstands the thermodynamic
test, whereas the impedance of the Drude model does not. We also perform a
phenomenological analysis of the thermal Casimir force and of the radiative
heat transfer through a vacuum gap between real metal plates. The
characterization of a metal by means of the Leontovich impedance of the Drude
model is shown to be inconsistent with experiment at separations of a few
hundred nanometers. A modification of the impedance of infrared optics is
suggested taking into account relaxation processes. The power of radiative heat
transfer predicted from this impedance is several times less than previous
predictions due to different contributions from the transverse electric
evanescent waves. The physical meaning of low frequencies in the Lifshitz
formula is discussed. It is concluded that new measurements of radiative heat
transfer are required to find out the adequate description of a metal in the
theory of electromagnetic fluctuations.Comment: 19 pages, 4 figures. svjour.cls is used, to appear in Eur. Phys. J.
Characterization of optical properties and surface roughness profiles: The Casimir force between real materials
The Lifshitz theory provides a method to calculate the Casimir force between
two flat plates if the frequency dependent dielectric function of the plates is
known. In reality any plate is rough and its optical properties are known only
to some degree. For high precision experiments the plates must be carefully
characterized otherwise the experimental result cannot be compared with the
theory or with other experiments. In this chapter we explain why optical
properties of interacting materials are important for the Casimir force, how
they can be measured, and how one can calculate the force using these
properties. The surface roughness can be characterized, for example, with the
atomic force microscope images. We introduce the main characteristics of a
rough surface that can be extracted from these images, and explain how one can
use them to calculate the roughness correction to the force. At small
separations this correction becomes large as our experiments show. Finally we
discuss the distance upon contact separating two rough surfaces, and explain
the importance of this parameter for determination of the absolute separation
between bodies.}Comment: 33 pages, 14 figures, to appear in Springer Lecture Notes in Physics,
Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni, David
Roberts, and Felipe da Ros
ELLIPSOMETRIC INVESTIGATION OF THE SILICON / ANODIC-OXIDE INTERFACE
On présente les résultats de mesures d'ellipsométrie effectuées pendant la croissance et le décapage de couches d'oxyde anodique sur le silicium dans 2M KOH. Il se produit des variations importantes de ψ et de Ɗ au moment où le décapage chimique atteint l'interface SiO2/Si, et aussi dans la première phase de l'anodisation. Les résultats sont interprétés par un changement dans la stoechiométrie et l'épaisseur d'une couche de transition SiOx (0⩽x⩽2).Ellipsometric measurements have been carried out during growth and etch back of anodic oxides on Si in 2M KOH. Pronounced variations in ψ and Ɗ occur as etching proceeds through the SiO2/Si interface and also during the initial stages of re-anodization. The results are interpreted in terms of changes in the stoichiometry and thickness of an SiOx (0⩽x⩽2) connective layer
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