Negative refractive index in coaxial plasmon waveguides

We theoretically show that coaxial waveguides composed of a metallic core, surrounded by a dielectric cylinder and clad by a metal outer layer exhibit negative refractive index modes over a broad spectral range in the visible. For narrow dielectric gaps (10 nm GaP embedded in Ag) a figure-of-merit of 18 can be achieved at λ_0 = 460 nm. For larger dielectric gaps the negative index spectral range extends well below the surface plasmon resonance frequency. By fine-tuning the coaxial geometry the special case of n = −1 at a figure-of-merit of 5, or n = 0 for a decay length of 500 nm can be achieved

Plasmon Dispersion in Coaxial Waveguides from Single-Cavity Optical Transmission Measurements

We determine the plasmon dispersion relation in coaxial waveguides composed of a circular channel separating a metallic core and cladding. Optical transmission measurements are performed on isolated coaxial nanoapertures fabricated on a Ag film using focused ion-beam lithography. The dispersion depends strongly on the dielectric material and layer thickness. Our experimental results agree well with an analytical model for plasmon dispersion in coaxial waveguides. We observe large phase shifts at reflection from the end facets of the coaxial cavity, which strongly affect the waveguide resonances and can be tuned by changing the coax geometry, composition, and surrounding dielectric index, enabling coaxial cavities with ultrasmall mode volumes

Active plasmonic devices and optical metamaterials

We studied active near-infrared metamaterials based on phase transition of vanadium oxide thin films, asymmetrically coupled split-ring resonators for narrowing resonance line-widths , field effect modulation of plasmon propagation and 3D single layer, plasmonic negative-index metamaterials

Plasmonic metamaterials

We experimentally and theoretically determine the plasmon dispersion in coaxial waveguides. We demonstrate strong optical confinement at energies below the surface plasmon resonance. Furthermore, we find that the reflection coefficients of the coax end facets can be strongly tuned by changing the coax dispersion and surrounding dielectric, which provides a new route to optical cavities with ultrasmall mode volumes

Global, Diffuse, Direct, and Ultraviolet Solar Irradiance Recorded in Malta and Atmospheric Component Influences

AbstractGlobal and diffuse shortwave (SW) and global erythemal (UVER) irradiances were measured in Malta, in the middle of Mediterranean Sea. The effect of solar zenith angle on these irradiances is studied using the measurements and simulations developed with a radiative transfer model. The role of ozone, scattering by gases, and aerosols is analyzed. Results show that ozone and Rayleigh scattering are the main drivers responsible for the behavior of UVER variations with SZA. In the case of global and diffuse irradiance, the role of aerosols is the principal determinant

A single-layer wide-angle negative-index metamaterial at visible frequencies

Metamaterials are materials with artificial electromagnetic properties defined by their sub-wavelength structure rather than their chemical composition. Negative-index materials (NIMs) are a special class of metamaterials characterized by an effective negative index that gives rise to such unusual wave behaviour as backwards phase propagation and negative refraction. These extraordinary properties lead to many interesting functions such as sub-diffraction imaging and invisibility cloaking. So far, NIMs have been realized through layering of resonant structures, such as split-ring resonators, and have been demonstrated at microwave to infrared frequencies over a narrow range of angles-of-incidence and polarization. However, resonant-element NIM designs suffer from the limitations of not being scalable to operate at visible frequencies because of intrinsic fabrication limitations, require multiple functional layers to achieve strong scattering and have refractive indices that are highly dependent on angle of incidence and polarization. Here we report a metamaterial composed of a single layer of coupled plasmonic coaxial waveguides that exhibits an effective refractive index of −2 in the blue spectral region with a figure-of-merit larger than 8. The resulting NIM refractive index is insensitive to both polarization and angle-of-incidence over a ±50° angular range, yielding a wide-angle NIM at visible frequencies

The Kalman condition for the boundary controllability of coupled parabolic systems. Bounds on biorthogonal families to complex matrix exponentials

International audienceThis paper is devoted to prove the controllability to trajectories of a system of $n$ one-dimensional parabolic equations when the control is exerted on a part of the boundary by means of $m$ controls. We give a general \textit{Kalman condition} (necessary and sufficient) and also present a construction and sharp estimates of a biothorgonal family in L^{2}(0,T; \C) to $\{ t^{j}e^{-\Lambda_{k}t}\}$.Cet article a pour but de démontrer la contrôlabilité des trajectoires d’un système de $n$ équations paraboliques en une dimension d’espace par $m$ contrôles exercés sur une partie du bord. On obtient une condition de Kalman (nécessaire et suffisante). La démonstration passe par la construction dans L^{2}(0,T; \C) d’une famille biorthogonale de la suite $\{ t^{j}e^{-\Lambda_{k}t}\}$ et par une estimation de la norme de ses éléments

Stars and brown dwarfs in the sigma Orionis cluster IV. IDS/INT and OSIRIS/GTC spectroscopy and Gaia DR2 astrometry

Context. Only a few open clusters are as important for the study of stellar and substellar objects, and their formation and evolution, as the young σ Orionis cluster. However, a complete spectroscopic characterisation of its whole stellar population is still missing. Aims. We filled most of that gap with a large spectroscopic and astrometric survey of targets towards σ Orionis. Eventually, it will be one of the open clusters with the lowest proportion of interlopers and the largest proportion of confirmed cluster members with known uncontrovertible youth features. Methods. We acquired 317 low-resolution optical spectra with the Intermediate Dispersion Spectrograph (IDS) at the 2.5 m Isaac Newton Telescope (INT) and the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias (GTC). We measured equivalent widths of Li i, Hα, and other key lines from these spectra, and determined spectral types. We complemented this information with Gaia DR2 astrometric data and other features of youth (mid-infrared excess, X-ray emission) compiled with Virtual Observatory tools and from the literature. Results. Of the 168 observed targets, we determined for the first time spectral types of 39 stars and equivalent widths of Li i and Hα of 34 and 12 stars, respectively. We identified 11 close (ρ </≈ 3 arcsec) binaries resolved by Gaia, of which three are new, 14 strong accretors, of which four are new and another four have Hα emission shifted by over 120 km s^(−1) , two juvenile star candidates in the sparse population of the Ori OB1b association, and one spectroscopic binary candidate. Remarkably, we found 51 non-clustermembers, 35 of which were previously considered as σ Orionis members and taken into account in high-impact works on, for example, disc frequency and initial mass function

Phase diagram and critical properties in the Polyakov--Nambu--Jona-Lasinio model

We investigate the phase diagram of the so-called Polyakov--Nambu--Jona-Lasinio model at finite temperature and nonzero chemical potential with three quark flavours. Chiral and deconfinement phase transitions are discussed, and the relevant order-like parameters are analyzed. The results are compared with simple thermodynamic expectations and lattice data. A special attention is payed to the critical end point: as the strength of the flavour-mixing interaction becomes weaker, the critical end point moves to low temperatures and can even disappear.Comment: Talk given at the 9th International Conference on Quark Confinement and the Hadron Spectrum - QCHS IX, Madrid, Spain, 30 August - September 201

Solos do campo experimental da Embrapa Algodão, em Patos-PB: levantamento detalhado e potencial edáfico.

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