Norbert Hubin

LASER GUIDE STAR FOR 3.6- AND 8-M TELESCOPES : PERFORMANCE AND ASTROPHYSICAL IMPLICATIONS

We have constructed an analytical model to simulate the behavior of an adaptive optics system coupled with a sodium laser guide star. The code is applied to a 3.6-m and 8m class telescopes. The results are given in terms of Strehl ratio and full width at half maximum of the point spread function. Two atmospheric models are used, one representing good atmospheric conditions (20 per cent of the time), the other median conditions. Sky coverage is computed for natural guide star and laser guide star systems, with two different methods. The first one is a statistical approach, using stellar densities, to compute the probability to find a nearby reference. The second is a cross-correlation of a science object catalogue and the USNO catalogue. Results are given in terms of percentage of the sky that can be accessed with given performances, and in terms of number of science object that can be observed, with Strehls greater than 0.2 and 0.1 in K and J bands.

Adaptive optics with four laser guide stars: correction of the cone effect in large telescopes

We study the performance of an adaptive optics (AO) system with four laser guide stars (LGSs) and a natural guide star (NGS). The residual cone effect with four LGSs is obtained by a numerical simulation. This method allows the adaptive optics system to be extended toward the visible part of the spectrum without tomographic reconstruction of three-dimensional atmospheric perturbations, resolving the cone effect in the visible. Diffraction-limited images are obtained with 17-arc ms precision in median atmospheric conditions at wavelengths longer than 600 nm. The gain achievable with such a system operated on an existing AO system is studied. For comparison, performance in terms of achievable Strehl ratio is also computed for a reasonable system composed of a 40 x 40 Shack-Hartmann wave-front sensor optimized for the I band. Typical errors of a NGS wave front are computed by use of analytical formulas. With the NGS errors and the cone effect, the Strehl ratio can reach 0.45 at 1.25 microm under good-seeing conditions with the Nasmyth Adaptive Optics System (NAOS; a 14 x 14 subpupil wave-front sensor) at the Very Large Telescope and 0.8 with a 40 x 40 Shack-Hartmann wave-front sensor.

Zero Noise Wavefront Sensor Development within the Opticon European Network

This activity, funded by ESO and the European Commission through the Opticon Network will attempt to define, fabricate and fully characterize the best possible detector working at visible wavelengths suitable for wavefront sensors in Adaptive Optics (AO) systems. The detector will be a split frame transfer array built by e2v technologies and called CCD220. The frame rate will be very fast (up to 1.2 kHz) while the readout noise will be kept extremely low (typically below 1 e - ). The goal of this paper is to justify the choice of detector: an EMCCD with 240×240 pixels and 8 outputs that will provide sub- electron readout noise at 1-1.2 kHz frame rate. This paper shows that, despite the fact that EMCDDs have an excess noise factor of 1.4 due to the charge multiplication process; their virtually zero read noise should allow them to outperform the classical CCD. Such detectors do not yet exist and must be developed. Moreover, this paper explains how the OPTICON European network is organized.

Manufacturing of the ESO adaptive optics facility

The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser driven adaptive telescope with a deformable mirror in its optical train, in this case the secondary 1.1m mirror, and four Laser Guide Stars (LGSs). This evolution implements many challenging technologies like the Deformable Secondary Mirror (DSM) including a thin shell mirror (1.1 m diameter and 2mm thin), the high power Na lasers (20W), the low Read-Out Noise (RON) WaveFront Sensor (WFS) camera (< 1e-) and SPARTA the new generation of Real Time Computers (RTC) for adaptive control. It also faces many problematic similar to any Extremely Large Telescope (ELT) and as such, will validate many technologies and solutions needed for the European ELT (E-ELT) 42m telescope. The AOF will offer a very large (7 arcmin) Field Of View (FOV) GLAO correction in J, H and K bands (GRAAL+Hawk-I), a visible integral field spectrograph with a 1 arcmin GLAO corrected FOV (GALACSI-MUSE WFM) and finally a LTAO 7.5 FOV (GALACSI-MUSE NFM). Most systems of the AOF have completed final design and are in manufacturing phase. Specific activities are linked to the modification of the 8m telescope in order to accommodate the new DSM and the 4 LGS Units assembled on its Center-Piece. A one year test period in Europe is planned to test and validate all modes and their performance followed by a commissioning phase in Paranal scheduled for 2014.

GRAAL: a seeing enhancer for the NIR wide-field imager Hawk-I

We describe the design and development status of GRAAL, the Ground-layer adaptive optics assisted by Laser, which will deliver enhanced images to the Hawk-I instrument on the VLT. GRAAL is an adaptive optics module, part of AOF, the Adaptive optics facility, using four Laser- and one natural guide-stars to measure the turbulence, and correcting for it by deforming the adaptive secondary mirror of a Unit telescope in the Paranal observatory. The outstanding feature of GRAAL is the extremely wide field of view correction, over 10 arcmin diameter, with an image enhancement of about 20% in average in K band. When observing GRAAL will provide FWHM better than 0.3 40% of the time. Besides the Adaptive optics facility deformable mirror and Laser guide stars, the system uses subelectron L3-CCD and a real-time computing platform, SPARTA. GRAAL completed early this year a final design phase shared internally and outsourced for its mechanical part by the Spanish company NTE. It is now in manufacturing, with a first light in the laboratory planned in 2011.

Adaptive Optics Facility: from an amazing present to a brilliant future...

The Adaptive Optics Facility (AOF) is an ESO project, which transformed Yepun, one of the four 8m telescopes in Paranal, into an adaptive telescope. This has been done by replacing the conventional secondary mirror of Yepun by a Deformable Secondary Mirror (DSM) and attaching four Laser Guide Stars (LGS) Units to its centerpiece. Additionally, two Adaptive Optics (AO) modules (GALACSI serving MUSE a 3D spectrograph, and GRAAL, serving Hawk I a wide field infrared imager) have been assembled onto the telescope Nasmyth adapters, each of them incorporating four LGS WaveFront Sensors (WFS) and one tip-tilt sensor used to control the DSM at 1 kHz frame rate. The complete AOF is installed on Yepun for more than one year now, and its commissioning is fully complete. This paper presents the most important and amazing features of the AOF, illustrated by some first science images obtained using MUSE/GALACSI in Ground Layer AO (GLAO) and Laser Tomography AO (LTAO) mode, and HAWK-I/GRAAL in GLAO mode. In the first part of the paper, on-sky performance of GRAAL and GALACSI is presented in terms of gain in image quality and even Strehl Ratio. Efficiency of the on-sky operation of the AOF is described. In the second part, future instruments making use of the AOF capabilities are presented.

NAOMI: the adaptive optics for the auxiliary telescopes of VLTI

The New Adaptive Optics Module for Interferometry (NAOMI) is ready to be installed at the 1.8-metre Auxiliary Telescopes (ATs) at ESO Paranal. NAOMI will make the existing interferometer performance less dependent on the seeing conditions. Fed with higher and more stable Strehl, the fringe tracker will achieve the fringe stability necessary to reach the full performance of the second-generation instruments GRAVITY and MATISSE. All four ATs will be equipped between September and November 2018 with a Deformable mirror (ALPAO DM-241), a 4*4 Shack– Hartmann adaptive optics system operating in the visible and an RTC based on SPARTA Light. During the last 6 months thorough system test has been made in laboratory to demonstrate the Adaptive Optics and chopping capability of NAOMI.

The AO in AOF

The long commissioning of the Adaptive Optics Facility (AOF) project has been completed shortly after this conference, providing AO correction to two Very Large Telescope (VLT) foci supported by an adaptive secondary mirror and four laser guide stars. Four AO modes are delivered: a Single Conjugate AO (SCAO) system for commissioning purpose, wide field and medium field Ground Layer AO (GLAO) for seeing improvement and narrow field Laser Tomography AO (LTAO) for ultimate performance. This paper intends to describe the implemented AO baseline and to highlight the most relevant results and lessons learned. In particular, it will address the control and reconstruction strategy, the wavefront sensing baseline and the online telemetry used to optimize the system online, estimate the turbulence profile and calibrate the misregistrations. Focusing on the LTAO mode, we will describe the tomography optimization, by exploring the reconstruction parameter space. Finally, on sky performance results will be presented both in terms of strehl ratio and limiting magnitude.

The Adaptive Optics Facility: Commissioning Progress and Results

In September 2016, the 14 crates containing the DSM system (Arsenault et al., 2013a; Manetti et al., 2014; Briguglio et al., 2014), totalling 9 tonnes and 50 cubic metres, were unpacked in the New Integration Hall (NIH) in Paranal. The system was re-assembled in the NIH and functionalities tested. It was an opportunity to cross-train our Paranal colleagues and demonstrate several handling operations, including the critical thin-shell mirror handling.

E-ELT M4 Unit updated design and prototype results

We present the current design of the E-ELT M4 deformable mirror consolidated at the conclusion of the Preliminary Design activity. The most prominent features of this system are the SiC Reference Body now mounted to the positioner by a whiffle-tree and cell structure, actuators bricks, capacitive sensors layout and new cooling concept. All this allowed achieving the challenging stability requirements demanded to the M4U, as proved by analysis and test results measured on the Demonstration Prototype, which has been updated to implement the current design. The final design and construction contract is now on-going: Final Design Review is planned on mid 2017 and delivery to site by late 2022.