101 research outputs found
Dielectric geometric phase optical elements from femtosecond direct laser writing
We propose to use femtosecond direct laser writing technique to realize
dielectric optical elements from photo-resist materials for the generation of
structured light from purely geometrical phase transformations. This is
illustrated by the fabrication and characterization of spin-to-orbital optical
angular momentum couplers generating optical vortices of topological charge
from 1 to 20. In addition, the technique is scalable and allows obtaining
microscopic to macroscopic flat optics. These results thus demonstrate that
direct 3D photopolymerization technology qualifies for the realization of
spin-controlled geometric phase optical elements.Comment: 6 figure
Optical bandgap formation in AlInGaN alloys
We report on the spectral dynamics of the reflectivity, site-selectively excited photoluminescence,photoluminescence excitation, and time-resolved luminescence in quaternary AlInGaN epitaxial layers grown on GaN templates. The incorporation of a few percents of In into AlGaN causes significant smoothening of the band-bottom potential profile in AlInGaN layers owing to improved crystal quality. An abrupt optical bandgap indicates that a nearly lattice-matched AlInGaN/GaN heterostructure with large energy band offsets can be grown for high-efficiency light-emitting devices
Luminescence in Highly Excited InGaN/GaN Multiple Quantum Wells Grown on GaN and Sapphire Substrates
We report on high-excitation luminescence spectroscopy in In x Ga 1−x N/GaN multiple quantum wells grown by MOCVD over sapphire and bulk GaN substrates. High excitation conditions enabled us to achieve a screening of the built-in field by free carriers. This allowed for the evaluation of the influence of band potential fluctuations due to the variation in In-content on efficiency of spontaneous and stimulated emission. InGaN/GaN multiple quantum wells grown on bulk GaN substrate exhibit a significantly lower stimulated emission threshold and thus enhanced lateral emission. Transient and dynamic properties of luminescence indicate a significant reduction in compositional disorder in homoepitaxially grown structures
Probing New Physics Models of Neutrinoless Double Beta Decay with SuperNEMO
The possibility to probe new physics scenarios of light Majorana neutrino
exchange and right-handed currents at the planned next generation neutrinoless
double beta decay experiment SuperNEMO is discussed. Its ability to study
different isotopes and track the outgoing electrons provides the means to
discriminate different underlying mechanisms for the neutrinoless double beta
decay by measuring the decay half-life and the electron angular and energy
distributions.Comment: 17 pages, 14 figures, to be published in E.P.J.
Broadband impedance spectroscopy of some Li+ and Vo** conducting solid electrolytes
The solid electrolyte Li3Ti1.5(PO4)3 compound has been synthesized by solid state reaction and studied by X-ray diffraction. At room temperature the compound belongs to rhombohedral symmetry (space group R3 ̅c) with six formula units in the unit cell. Li3Ti1.5(PO4)3, Li3xLa2/3–xTiO3 (where x = 0.12) Li+-ion conducting, Ce0.8Gd0.2O1.9, (ZrO2)92(Y2O3)8 with fast oxygen vacancy transport ceramic samples were investigated in the frequency range from 1 Hz to 3 GHz in the temperature interval (300-700) K by impedance spectroscopy methods. Two dispersion regions in ionic conductivity spectra for investigated ceramic samples have been found. The dispersions have been attributed to relaxation processes in grain boundaries and in grains of the ceramics
Results of the BiPo-1 prototype for radiopurity measurements for the SuperNEMO double beta decay source foils
The development of BiPo detectors is dedicated to the measurement of
extremely high radiopurity in Tl and Bi for the SuperNEMO
double beta decay source foils. A modular prototype, called BiPo-1, with 0.8
of sensitive surface area, has been running in the Modane Underground
Laboratory since February, 2008. The goal of BiPo-1 is to measure the different
components of the background and in particular the surface radiopurity of the
plastic scintillators that make up the detector. The first phase of data
collection has been dedicated to the measurement of the radiopurity in
Tl. After more than one year of background measurement, a surface
activity of the scintillators of (Tl) 1.5
Bq/m is reported here. Given this level of background, a larger BiPo
detector having 12 m of active surface area, is able to qualify the
radiopurity of the SuperNEMO selenium double beta decay foils with the required
sensitivity of (Tl) 2 Bq/kg (90% C.L.) with a six
month measurement.Comment: 24 pages, submitted to N.I.M.
Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors
We have constructed a GEANT4-based detailed software model of photon
transport in plastic scintillator blocks and have used it to study the NEMO-3
and SuperNEMO calorimeters employed in experiments designed to search for
neutrinoless double beta decay. We compare our simulations to measurements
using conversion electrons from a calibration source of and show
that the agreement is improved if wavelength-dependent properties of the
calorimeter are taken into account. In this article, we briefly describe our
modeling approach and results of our studies.Comment: 16 pages, 10 figure
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