The CHARA Array is the longest baseline optical interferometer in the world. Operated with natural seeing, it has delivered landmark sub-milliarcsecond results in the areas of stellar imaging, binaries, and stellar diameters. However, to achieve ambitious observations of faint targets such as young stellar objects and active galactic nuclei, higher sensitivity is required. For that purpose, adaptive optics are developed to correct atmospheric turbulence and non-common path aberrations between each telescope and the beam combiner lab. This paper describes the AO software and its integration into the CHARA system. We also report initial on-sky tests that demonstrate an increase of scientific throughput by sensitivity gain and by extending useful observing time in worse seeing conditions. Our 6 telescopes and 12 AO systems with tens of critical alignments and control loops pose challenges in operation. We describe our methods enabling a single scientist to operate the entire system.
HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, provide a summary of the instrument’s design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.
Adaptive-Optics (AO) pre-compensation of atmospheric turbulence effects is one of the most promising technologies for achieving very high throughput optical GEO feeder links. However, its great performance has been proven mostly through numerical simulations until now, and experimental work on the subject is still at a very preliminary stage . The FEEDELIO experiment (FEEDELIO for FEEDEr Link adaptive Optics), contracted to ONERA by ESA and described in this paper, goes one step further towards an experimental validation of this concept.
This paper describes the experimental implementation of an AO pre-compensated link on a 13 km slant path in Tenerife, Canary Islands. This experiment is designed to be representative of a GEO feeder link, and aims at demonstrating a significant increase of the mean received power and decrease of the power fluctuations thanks to AO. It will also allow to study the impact of the point-ahead angle on overall performance of the AO system.
The FEEDELIO experiment is planned for spring 2019.
Research on III-nitride intersubband (ISB) transitions in the THz spectral range is motivated by the large LO-phonon energy of GaN, which should permit device operation with limited thermal interference, and at infrared wavelengths inaccessible to other III-V compounds due to Reststrahlen absorption. A main challenge to extend the polar GaN-ISB technology towards the THz region comes from the polarization-induced internal electric field, which imposes an additional confinement that increases the energetic distance between the electronic levels. In order to surmount this constraint, we propose alternative multi-layer quantum well designs that create a pseudo-square potential profile with symmetric wavefunctions . The robustness of these designs and their integration in device architectures requiring tunneling transport will be discussed.
An alternative approach to obtain square potential profiles is the use of nonpolar crystallographic orientations. In this contribution, we present an experimental study of THz ISB transitions in m-plane GaN/AlGaN quantum wells grown on free-standing m-GaN . For Al contents below 15%, such structures can be grown without epitaxially-induced extended defects. We demonstrate nonpolar quantum wells which display ISB transitions in the 7-10 THz band, and we will discuss the effect of the doping density in the quantum wells on the transition energy and line width. Finally, we will present a comparative study using silicon and germanium as n-type dopants.
 M. Beeler, et al., Appl. Phys. Lett. 105, 131106 (2014)
 C.B. Lim, et al., Nanotechnology 26, 435201 (2015); Nanotechnology 27, 145201 (2016).