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Publicações

Publicações por Carlos Manuel Correia

2016

On-line estimation of atmospheric turbulence parameters and outer-scale profiling

Autores
Guesalaga, A; Neichel, B; Correia, C; Butterley, T; Osborn, J; Masciadri, E; Fusco, T; Sauvage, JF;

Publicação
ADAPTIVE OPTICS SYSTEMS V

Abstract
Estimating the outer scale profile, L0(h) in the context of current very large and future extremely large telescopes is crucial, as it impacts the on-line estimation of turbulence parameters (Cn2(h), r0, ?0 and t0) and the performance of Wide Field Adaptive Optics (WFAO) systems. We describe an on-line technique that estimates L0(h) using AO loop data available at the facility instruments. It constructs the cross-correlation functions of the slopes of two or more wavefront sensors, which are fitted to linear combinations of theoretical responses for individual layers with different altitudes and outer scale values. We analyze some restrictions found in the estimation process, which are general to any measurement technique. The insensitivity of the instrument to large values of outer scale is one of them, as the telescope becomes blind to outer scales larger than its diameter. Another problem is the contradiction between the length of data and the stationarity assumption of the turbulence (turbulence parameters may change during the data acquisition time). Our method effectively deals with problems such as noise estimation, asymmetric correlation functions and wavefront propagation effects. It is shown that the latter cannot be neglected in high resolution AO systems or strong turbulence at high altitudes. The method is applied to the Gemini South MCAO system (GeMS) that comprises five wavefront sensors and two DMs. Statistical values of L0(h) at Cerro Pachón from data acquired with GeMS during three years are shown, where some interesting resemblance to other independent results in the literature are shown.

2016

Natural guide-star processing for wide-field laser-assisted AO systems

Autores
Correia, CM; Neichel, B; Conan, JM; Petit, C; Sauvage, JF; Fusco, T; Vernet, JDR; Thatte, N;

Publicação
ADAPTIVE OPTICS SYSTEMS V

Abstract
Sky-coverage in laser-Assisted AO observations largely depends on the system's capability to guide on the faintest natural guide-stars possible. Here we give an up-To-date status of our natural guide-star processing tailored to the European-ELT's visible and near-infrared (0.47 to 2.45 µm) integral field spectrograph-Harmoni. We tour the processing of both the isoplanatic and anisoplanatic tilt modes using the spatio-Angular approach whereby the wavefront is estimated directly in the pupil plane avoiding a cumbersome explicit layered estimation on the 35-layer profiles we're currently using. Taking the case of Harmoni, we cover the choice of wave-front sensors, the number and field location of guide-stars, the optimised algorithms to beat down angular anisoplanatism and the performance obtained with different temporal controllers under split high-order/low-order tomography or joint tomography. We consider both atmospheric and far greater telescope wind buffeting disturbances. In addition we provide the sky-coverage estimates thus obtained.

2016

William Herschel Telescope site characterization using the MOAO pathfinder CANARY on-sky data

Autores
Martin, OA; Correia, CM; Gendron, E; Rousset, G; Vidal, F; Morris, TJ; Basden, AG; Myers, RM; Ono, YH; Neichel, B; Fusco, T;

Publicação
ADAPTIVE OPTICS SYSTEMS V

Abstract
CANARY is the Multi-Object Adaptive Optics (MOAO) pathfinder for the future MOAO-Assisted Integral-Field Units (IFU) proposed for Extremely Large Telescopes (ELT). The MOAO concept relies on tomographically reconstructing the turbulence using multiple measurements along different lines of sight. Tomography requires the knowledge of the statistical turbulence parameters, commonly recovered from the system telemetry using a dedicated profiling technique. For demonstration purposes with the MOAO pathfinder CANARY, this identification is performed thanks to the Learn & Apply (L&A) algorithm, that consists in model-fitting the covariance matrix of WFS measurements dependant on relevant parameters: Cn2(h) profile, outer scale profile and system mis-registration. We explore an upgrade of this algorithm, the Learn 3 Steps (L3S) approach, that allows one to dissociate the identification of the altitude layers from the ground in order to mitigate the lack of convergence of the required empirical covariance matrices therefore reducing the required length of data time-series for reaching a given accuracy. For nominal observation conditions, the L3S can reach the same level of tomographic error in using five times less data frames than the L&A approach. The L3S technique has been applied over a large amount of CANARY data to characterize the turbulence above the William Herschel Telescope (WHT). These data have been acquired the 13th, 15th, 16th, 17th and 18th September 2013 and we find 0.67"/8.9m/3.07m.s-1 of total seeing/outer scale/wind-speed, with 0.552"/9.2m/2.89m.s-1 below 1.5 km and 0.263"/10.3m/5.22m.s-1 between 1.5 and 20 km. We have also determined the high altitude layers above 20 km, missed by the tomographic reconstruction on CANARY, have a median seeing of 0.187" and have occurred 16% of observation time.

2016

The Adaptive Optics modes for HARMONI - From Classical to Laser Assisted Tomographic AO

Autores
Neichel, B; Fusco, T; Sauvage, JF; Correia, C; Dohlen, K; El Hadi, K; Blanco, L; Schwartz, N; Clarke, F; Thatte, NA; Tecza, M; Paufique, J; Vernet, J; Le Louarn, M; Hammersley, P; Gach, JL; Pascal, S; Vola, P; Petit, C; Conan, JM; Carlotti, A; Verinaud, C; Schnetler, H; Bryson, I; Morris, T; Myers, R; Hugot, E; Gallie, AM; Henry, DM;

Publicação
ADAPTIVE OPTICS SYSTEMS V

Abstract
HARMONI is a visible and NIR integral field spectrograph, providing the E-ELT's core spectroscopic capability at first light. HARMONI will work at the diffraction limit of the E-ELT, thanks to a Classical and a Laser Tomographic AO system. In this paper, we present the system choices that have been made for these SCAO and LTAO modules. In particular, we describe the strategy developed for the different Wave-Front Sensors: pyramid for SCAO, the LGSWFS concept, the NGSWFS path, and the truth sensor capabilities. We present first potential implementations. And we asses the first system performance.

2016

On-sky MOAO performance evaluation of RAVEN

Autores
Ono, YH; Correia, CM; Lardière, O; Andersen, DR; Oya, S; Akiyama, M; Gamroth, D; Jackson, K; Martin, O; Bradley, C;

Publicação
ADAPTIVE OPTICS SYSTEMS V

Abstract
This paper presents the AO performance we got on-sky with RAVEN, a Multi-Object Adaptive Optics (MOAO) technical and science demonstrator installed and tested at the Subaru telescope. We report Ensquared-Energy (EE) and Full Width at Half Maximum (FWHM) measured from science images on Subaru's IRCS taken during all of the on-sky observing runs. We show these metrics as function of different AO modes and atmospheric conditions for two asterisms of natural guide stars. The performances of the MOAO and Ground-Layer AO (GLAO) modes are between the classical Single-Conjugate AO (SCAO) and seeing-limited modes. We achieve the EE of 30% in H-band with the MOAO correction, which is a science requirement for RAVEN. The MOAO provides sightly better performance than the GLAO mode in both asterisms. One of the reasons which cause this small difference between the MOAO and GLAO modes may be the strong GL contribution. Also, the performance of the MOAO modes is affected by the accuracy of the on-sky turbulence profiling by the SLOpe Detection And Ranging (SLODAR) method.

2016

Laser guide star spot shrinkage for affordable wavefront sensors

Autores
Jahn, W; Hugot, E; Fusco, T; Neichel, B; Ferrari, M; Correia, C; Pueyo, L; Dohlen, K; Pascal, S; Vola, P; Sauvage, JF; El Hadi, K; Gach, JL;

Publicação
ADAPTIVE OPTICS SYSTEMS V

Abstract
Innovative optical designs allow tackling the spot elongation issues in Shack-Hartman based laser guide star wavefront sensors. We propose two solutions using either a combination of two arrays of freeform microlenses, or a combination of freeform optics, to perform a shrinkage of the laser spots as well as a magnification of the SH focal plane. These approaches will drastically reduce the number of needed pixels, thus making possible the use of existing detectors. We present the recent advances on this activity as well as the estimation of performance, linearity and sensitivity of the compressed system in presence of aberrations.

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