The team is conducting numerical modeling work in AO, developed within the Code for Adaptive Optics Systems (CAOS) Problem-Solving Environment (PSE) and its eponymous scientific package, the CAOS Software Package. This tool has recently benefited from a substantial overhaul, including modeling of large AO systems multi-reference and multi-conjugated field, an ideal wavefront sensor (WFS) and a state representation of the control law (Carbillet et al. 2016). Studies were carried out on topics such as comparison and agreement with the semi-analytic code PAOLA (Carbillet & Jolissaint 2012), the M4 type mirror "Adaptive secondary" of the E-ELT (Carbillet et al. 2012) and the performance of an AO system for the SALT (Catala et al. 2012). The CAOS PSE also integrates tools for the deconvolution of post-AO images through the development of the AIRY Software Package (La Camera et al. 2012, 2016). The first application of a super-resolution algorithm to VLT/NACO data was thus performed (Carbillet et al. 2013), two variants of blind deconvolution with Strehl constraints have been implemented (Carbillet et al. 2014) and a high dynamic deconvolution algorithm has been proposed (Benfenati et al. 2016).
As part of our activities in post AO imaging, especially in the case of partial correction which is relevant for wide-field AO, visible AO and/or Laser Guide Star (LGS) AO, we test methods based on advanced short exposure imaging techniques. This work fits within the context of the HiPIC instrument (High resolution Angular in the Visible and Near-Infrared at Calern) dedicated to fast visible / near-infrared imaging developed at C2PU (Planet and Universe Pedagogical Center) and intended to take advantage of the CIAO system (Calern Imaging Adaptive Observatory, 10x10 Shack-Hartmann, ALPAO mirror, RTC architecture based on Subaru/SCExAO), which is currently being integrated and for which we got the first performance results in standard AO mode.
The team also participates in the very wide field AO instrument imaka, through a collaboration with the Institute for Astronomy at the University of Hawaii. This prototype, with a 24' field (scientific field 10'), saw its first light at the University of Hawaii's 88" telescope on Mauna Kea at the end of 2016 and produces images of 0.3" in the visible range. It is used to study the AO performance as a function of the atmospheric conditions, and new techniques for measuring the turbulence profile and its phase structure function have been developed for this purpose.
In pragmatic terms, from the point of view of Linear control theory, AO instruments are multi-variables dynamical systems subject to input disturbances (atmospheric turbulence, vibrations, etc.) and uncertainties (delays, isolated non-linearities) that can adequately be taken into account by robust control methods (linear quadratic Gaussian synthesis, LQG, or H∞, see Folcher et al. 2013). This activity includes rejection of vibrations, taking into account the saturation of tilt mirrors (Folcher et al. 2013), as well as steering high-performance telescopes. We also proposed a Robust control scheme for monitoring fringes in optical interferometry, a most critical question for modern ground-based interferometers (Folcher et al. 2014).
Calibrations, metrology, instrumental stability
The qualification of the Dome C site was completed, in particular with the development of a copy of PBL, modified to be able to face the difficult conditions of the Antarctic winter, and producing many results (e.g., Ziad et al. 2013). A prospective study for a Wide field AO system that best matches the specific atmospheric characteristics of Dome C was carried out (Carbillet et al. 2017). These results allow to start considering real AO applications in Antarctica with the Concordia base at Dome C as a preferred site. In particular, improvements of the ASTEP photometer (characterization of exoplanetary transits) are being considered, by adding adaptive correction (simple tip-tilt or ground layer low order correction of a large field of view). Technological R & D collaborations on AO components are currently developing in this direction (astronomy in Antarctica), but will benefit all instruments where compactness and versatility is essential, eg. autonomous observing stations, a prototype of which is currently in development at OCA.