Nonlocal conductance spectroscopy of Andreev bound states: Symmetry relations and BCS charges

Two-terminal conductance spectroscopy of superconducting devices is a common tool for probing Andreev and Majorana bound states. Here, we study theoretically a three-terminal setup, with two normal leads coupled to a grounded superconducting terminal. Using a single-electron scattering matrix, we derive the subgap conductance matrix for the normal leads and discuss its symmetries. In particular, we show that the local and the nonlocal elements of the conductance matrix have pairwise identical antisymmetric components. Moreover, we find that the nonlocal elements are directly related to the local BCS charges of the bound states close to the normal probes and we show how the BCS charge of overlapping Majorana bound states can be extracted from experiments.Comment: 7 page

Coherent combining of high brightness tapered amplifiers for efficient non-linear conversion

International audienceWe report on coherent beam combining of three high brightness tapered amplifiers seeded by a single-frequency laser at λ = 976 nm in a simple architecture with efficiently-cooled emitters. The maximal combined power of 12.9 W is achieved at a combining efficiency of > 65 % limited by the intrinsic beam quality of the amplifiers. The coherent combining cleans up the spatial profile, as the power content in the central lobe increases up to 86 %. This high-brightness infrared beam is converted into the visible by second harmonic generation, and results in a high non-linear conversion efficiency of 4.5 %/W and a maximum power over 2 W at 488 nm, limited by thermal effects in the PPLN

Isotopic and spin selectivity of H_2 adsorbed in bundles of carbon nanotubes

Due to its large surface area and strongly attractive potential, a bundle of carbon nanotubes is an ideal substrate material for gas storage. In addition, adsorption in nanotubes can be exploited in order to separate the components of a mixture. In this paper, we investigate the preferential adsorption of D_2 versus H_2(isotope selectivity) and of ortho versus para(spin selectivity) molecules confined in the one-dimensional grooves and interstitial channels of carbon nanotube bundles. We perform selectivity calculations in the low coverage regime, neglecting interactions between adsorbate molecules. We find substantial spin selectivity for a range of temperatures up to 100 K, and even greater isotope selectivity for an extended range of temperatures,up to 300 K. This isotope selectivity is consistent with recent experimental data, which exhibit a large difference between the isosteric heats of D_2 and H_2 adsorbed in these bundles.Comment: Paper submitted to Phys.Rev. B; 17 pages, 2 tables, 6 figure

Recent progress in brightness scaling by coherent beam combining of tapered amplifiers for efficient high power frequency doubling

International audienceHigh brightness diode laser beam combining techniques are in demand for efficient high power nonlinear conversion. Coherent beam combining (CBC) is the only method that has the potential for brightness scaling by maintaining one single narrow spectral linewidth. CBC in a master oscillator power amplifier (MOPA) configuration using a small number of efficiently cooled tapered amplifiers is a promising approach for efficient brightness scaling in a simple architecture. We present the application of such a source based on CBC of three tapered amplifiers seeded by a DFB laser at λ = 976 nm for second harmonic generation (SHG). A maximum power of 2.1 W at 488 nm was generated by SHG in a MgO:PPLN bulk crystal limited by thermal effects. A clear benefit of the beam clean-up resulting from the CBC setup was documented leading to an improved nonlinear efficiency. As part of our ongoing studies into further brightness scaling in CBC architectures, we present an experimental analysis of the phase dynamics of tapered amplifiers in quasi continuous operation (QCW) at high currents. Furthermore, we are investigating different amplifier designs for improved beam quality at high powers and therefore improved combining efficiency

A 1500 deg2 near infrared proper motion catalogue from the UKIDSS Large Area Survey

The United Kingdom Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) began in 2005, with the start of the UKIDSS programme as a 7 year effort to survey roughly 4000 deg2 at high Galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of two epoch J band observations, with an epoch baseline greater than 2 years to calculate proper motions. We present a near-infrared proper motion catalogue for the 1500 deg2 of the two epoch LAS data, which includes 135 625 stellar sources and a further 88 324 with ambiguous morphological classifications, all with motions detected above the 5σ level. We developed a custom proper motion pipeline which we describe here. Our catalogue agrees well with the proper motion data supplied for a 300 deg2 subset in the current Wide Field Camera Science Archive (WSA) 10th data release (DR10) catalogue, and in various optical catalogues, but it benefits from a larger matching radius and hence a larger upper proper motion detection limit. We provide absolute proper motions, using LAS galaxies for the relative to absolute correction. By using local second-order polynomial transformations, as opposed to linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by the UKIDSS pipeline. We present the results of proper motion searches for new brown dwarfs and white dwarfs. We discuss 41 sources in the WSA DR10 overlap with our catalogue with proper motions >300 mas yr−1, several of which are new detections. We present 15 new candidate ultracool dwarf binary systems