Measurement of the temperature of an ultracold ion source using time-dependent electric fields

We report on a measurement of the characteristic temperature of an ultracold rubidium ion source, in which a cloud of laser-cooled atoms is converted to ions by photo-ionization. Extracted ion pulses are focused on a detector with a pulsed-field technique. The resulting experimental spot sizes are compared to particle-tracking simulations, from which a source temperature $T = (1 \pm 2)$ mK and the corresponding transversal reduced emittance $\epsilon_r = 7.9 X 10^{-9}$ m rad $\sqrt{\rm{eV}}$ are determined. We find that this result is likely limited by space charge forces even though the average number of ions per bunch is 0.022.Comment: 8 pages, 11 figure

Ab initio electronic structure, optical, and magneto-optical properties of MnGaAs digital ferromagnetic heterostructures

We report on a theoretical study of the electronic, optical, and magneto-optical properties of digital ferromagnetic heterostructures based on Mn delta-doped GaAs. We consider different structures corresponding to Mn contents within the range 12%-50% and we study how the system changes as a function of the doping concentration. Our first-principles approach includes the spin-orbit interaction in a fully relativistic pseudopotential scheme and the local-field effect in the description of the optical absorption. We show that Mn d-doped GaAs shares many properties with the uniformly doped Ga1-xMnxAs system, i.e., half-metallicity, similar absorption spectra, and moderate Kerr rotation angles in the visible spectral region

Non-linear optical susceptibilities, Raman efficiencies and electrooptic tensors from first-principles density functional perturbation theory

The non-linear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach is based on the 2n + 1 theorem applied to an electric-field-dependent energy functional. We report the expressions for the calculation of the non-linear optical susceptibilities, Raman scattering efficiencies and electrooptic coefficients. Different formulations of third-order energy derivatives are examined and their convergence with respect to the k-point sampling is discussed. We apply our method to a few simple cases and compare our results to those obtained with distinct techniques. Finally, we discuss the effect of a scissors correction on the EO coefficients and non-linear optical susceptibilities

Calidad de agua para uso recreativo del Río Ctalamochita en Villa María, Córdoba, Argentina

El Río Tercero o Ctalamochita a lo largo de la ciudad de Villa María, Córdoba, Argentina, es utilizado con fines recreativos, entre otros. El objetivo de este trabajo es evaluar la calidad del agua para tal uso en el tramo correspondiente a la ciudad, a través del análisis de variables microbiológicas, fisicoquímicas y del índice de calidad de agua (WQI) del Canadian Council of Ministers of the Environment. Para ello se realiza el muestreo del río aguas arriba, en puntos intermedios y aguas abajo en distintos momentos del año, abarcando un periodo de dos años (de octubre 2017 a septiembre 2018). Se determinaron coliformes totales, coliformes termotolerantes y Escherichia coli. Además, se registraron la temperatura, pH, turbiedad, sólidos totales, demanda biológica de oxígeno (DBO5), demanda química de oxígeno, oxígeno disuelto, nitratos y nitritos. Los resultados muestran que los coliformes totales superaron el límite permitido en el 60 % de las muestras; los coliformes termotolerantes son acordes con la normativa en el 100 % de las muestras y la determinación de E. coli; sólo un valor supera el límite establecido. El WQI resultante es “Bueno” para dos de los sitios estudiados, mientras que aguas abajo, en Barrancas del Río, es “Marginal” (WQI = 62.2). Se concluye que en las zonas estudiadas, el uso recreativo no implicaría un riesgo para la salud humana. Sin embargo, es importante identificar los factores que influyen en el decrecimiento del WQI luego de atravesar la ciudad y las posibilidades de actuación sobre los mismos, si se quieren lograr mejoras en dicho tramo

Phonons and related properties of extended systems from density-functional perturbation theory

This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudo-potential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long wave-length vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic

Modeling challenges for high-efficiency visible light-emitting diodes

In order to predict through numerical simulation the optical and carrier transport properties of GaN-based light-emitting diodes (LEDs), a genuine quantum approach should be combined with an atomistic description of the electronic structure. However, computational considerations have elicited the empirical inclusion of quantum contributions within conventional semiclassical drift-diffusion approaches. The lack of first-principles validation tools has left these \u201cquantum corrections\u201d largely untested, at least in the context of LED simulation. We discuss here the results obtained comparing state-of-the-art commercial numerical simulators, in order to assess the predictive capabilities of some of the most important quantum-based models complementing the drift-diffusion equations

Performance predictions for a laser intensified thermal beam for use in high resolution Focused Ion Beam instruments

Photo-ionization of a laser-cooled and compressed atomic beam from a high-flux thermal source can be used to create a high-brightness ion beam for use in Focus Ion Beam (FIB) instruments. Here we show using calculations and Doppler cooling simulations that an atomic rubidium beam with a brightness of $2.1 \times 10^7 A/(m^2\,sr\,eV)$ at a current of 1 nA can be created using a compact 5 cm long 2D magneto-optical compressor which is more than an order of magnitude better than the current state of the art Liquid Metal Ion Source.Comment: 8 pages, 7 figures submitted to: Phys. Rev.