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

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

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

Double-scaled potential profile in a group-III nitride alloy revealed by Monte Carlo simulation of exciton hopping

The temperature dependences of the peak position and width of the photoluminescence band in Al0.1In0.01Ga0.89N layers were explained by Monte Carlo simulation of exciton localization and hopping. The introduction of a doubled-scaled potential profile due to inhomogeneous distribution of indium allowed obtaining a good quantitative fit of the experimental data. Hopping of excitons was assumed to occur through localized states distributed on a 16 meV energy scale within the In-rich clusters with the average energy in these clusters dispersed on a larger (42 meV) scale