Search

Following the arrival of MATISSE, the second-generation of VLTI instrumentation is now complete and was simultaneously enhanced by a major facility upgrade including the NAOMI Adaptive Optics on the Auxiliary Telescopes. On the Unit Telescopes, significant efforts were also made to improve the injection stability into VLTI instruments. On top of GRAVITY's own evolution, its fringe tracker is now being used to allow coherent integrations on MATISSE (the so-called GRA4MAT project). Meanwhile, operations also evolved to be more flexible and make the most of an extended observing parameter space. In this context, we present an overview of the current VLTI performances. Finally, we will report on on-going improvements such as the extension of the longest baselines.

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 near-infrared GRAVITY instrument has become a fully operational spectro-imager, while expanding its capability to support astrometry of the key Galactic Centre science. The mid-infrared MATISSE instrument has just arrived on Paranal and is starting its commissioning phase. NAOMI, the new adaptive optics for the Auxiliary Telescopes, is about to leave Europe for an installation in the fall of 2018. Meanwhile, the interferometer infrastructure has continuously improved in performance, in term of transmission and vibrations, when used with both the Unit Telescopes and Auxiliary Telescopes. These are the highlights of the last two years of the VLTI 2nd generation upgrade started in 2015.

The New Adaptive Optics Module for Interferometry (NAOMI) will be developed for and installed at the 1.8-metre Auxiliary Telescopes (ATs) at ESO Paranal. The goal of the project is to equip all four ATs with a low-order Shack– Hartmann adaptive optics system operating in the visible. By improving the wavefront quality delivered by the ATs for guide stars brighter than R = 13 mag, NAOMI will make the existing interferometer performance less dependent on the seeing conditions. Fed with higher and more stable Strehl, the fringe tracker(s) will achieve the fringe stability necessary to reach the full performance of the second-generation instruments GRAVITY and MATISSE.

For two years starting in February 2014, the AO modules GRAAL for HAWK-I and GALACSI for MUSE of the Adaptive Optics Facility project have undergone System Testing at ESO's Headquarters. They offer four different modes: NGS SCAO, LGS GLAO in the IR, LGS GLAO and LTAO in the visible. A detailed characterization of those modes was made possible by the existence of ASSIST, a test bench emulating an adaptive VLT including the Deformable Secondary Mirror, a star simulator and turbulence generator and a VLT focal plane re-imager. This phase aimed at validating all the possible components and loops of the AO modules before installation at the actual VLT that comprises the added complexity of real LGSs, a harsher non-reproducible environment and the adaptive telescope control. In this paper we present some of the major results obtained and challenges encountered during the phase of System Tests, like the preparation of the Acquisition sequence, the testing of the Jitter loop, the performance optimization in GLAO and the offload of low-order modes from the DSM to the telescope (restricted to the M2 hexapod). The System Tests concluded with the successful acceptance, shipping, installation and first commissioning of GRAAL in 2015 as well as the acceptance and shipping of GALACSI, ready for installation and commissioning early 2017.

The Adaptive Optics Facility is an ESO project aiming at converting Yepun, one of the four 8m telescopes in Paranal, into an adaptive telescope. This is done by replacing the current conventional secondary mirror of Yepun by a Deformable Secondary Mirror (DSM) and attaching four Laser Guide Star (LGS) Units to its centerpiece. In the meantime, two Adaptive Optics (AO) modules have been developed incorporating each four LGS WaveFront Sensors (WFS) and one tip-tilt sensor used to control the DSM at 1 kHz frame rate. The four LGS Units and one AO module (GRAAL) have already been assembled on Yepun. Besides the technological challenge itself, one critical area of AOF is the AO control strategy and its link with the telescope control, including Active Optics used to shape M1. Another challenge is the request to minimize the overhead due to AOF during the acquisition phase of the observation. This paper presents the control strategy of the AOF. The current control of the telescope is first recalled, and then the way the AO control makes the link with the Active Optics is detailed. Lab results are used to illustrate the expected performance. Finally, the overall AOF acquisition sequence is presented as well as first results obtained on sky with GRAAL.

GALACSI is the Adaptive Optics (AO) system serving the instrument MUSE in the framework of the Adaptive Optics Facility (AOF) project. Its Narrow Field Mode (NFM) is a Laser Tomography AO (LTAO) mode delivering high resolution in the visible across a small Field of View (FoV) of 7.5" diameter around the optical axis. From a reconstruction standpoint, GALACSI NFM intends to optimize the correction on axis by estimating the turbulence in volume via a tomographic process, then projecting the turbulence profile onto one single Deformable Mirror (DM) located in the pupil, close to the ground. In this paper, the laser tomographic reconstruction process is described. Several methods (virtual DM, virtual layer projection) are studied, under the constraint of a single matrix vector multiplication. The pseudo-synthetic interaction matrix model and the LTAO reconstructor design are analysed. Moreover, the reconstruction parameter space is explored, in particular the regularization terms. Furthermore, we present here the strategy to define the modal control basis and split the reconstruction between the Low Order (LO) loop and the High Order (HO) loop. Finally, closed loop performance obtained with a 3D turbulence generator will be analysed with respect to the most relevant system parameters to be tuned.

SPHERE instrument [1] (Spectro-Polarimetry High-contrast Exoplanet Research) is a second generation ESO instrument dedicated to high contrast imaging, and exoplanet direct detection and characterisation. The overall performance of XAO system of SPHERE, as well as the optimal control law for turbulence correction, are presented in dedicated papers [5,6]. The global performance of the instrument and of all observing modes of SPHERE is done in [4]. The strategy of Wave-front Sensing [WFS] in SPHERE relies on two faces, and is thoroughly discussed in this paper. Firstly, extreme adaptive optics (XAO) is required for both turbulence and quasi-static pattern compensation. Particularly, the high frame rate and large subaperture numbers of the Shack-Hartmann WFS allows SAXO to optimally measure and compensate for atmospherical turbulence. Moreover, the spatial filtering [7,8] allows one to deepen the contrast curve, and is automatically adjusted on turbulence level to provide the best performance. Finally, a dedicated calibration procedure based on focal-plane wave-front sensing is optimized for NCPA compensation on the coronagraphic device, ensuring the best compensation of quasi-static speckle. Secondly, a high robustness to faint magnitude guide star allows SAXO to address a large panel of targets for exoplanet detection and characterization. This is only made possible by the joint use of a dedicated Wave- Front Sensing for turbulence, EMCCD detector capability, and adaptation of the system to the star magnitude. The noise propagation has been carefully monitored and optimized. The weighted center of gravity gives an optimal trade-off between performance with respect to noise, and complexity of implementation. The use of an EMCCD detector allows a powerful noise reduction on the wave-front sensor detector. And finaly, 5 SAXO observing modes are defined in order to cover all star magnitudes up to 16, with systematic optimal performance. During the whole assembly integrations and test period, choices have been done to optimise the trade-off between performance, robustness, and simplicity of use. The self-adaptation and auto-calibration of the instrument has been a strong investment, as well as developing a great simplicity of use. We describe here the actions taken to reach this level of operation for SPHERE. Finally, perspective are withdrawn for improving the strategy of WFS in the framework of future XAO instrumentations in E-ELT.

The New Adaptive Optics Module for Interferometry (NAOMI)1 is the future low order adaptive optics system to be developed for and installed at the ESO 1.8 m Auxiliary Telescopes (ATs). The four ATs2 are designed for interferometry which they are essentially dedicated for. Currently the AT’s are equipped with a fast, visible tip-tilt sensor called STRAP3 (System for Tip/tilt Removal with Avalanche Photodiodes), and the corrections are applied through a tip-tilt mirror. The goal is to equip all four ATs with a low-order Shack-Hartmann system operating in the visible for the VLTI dual feed light beams in place of the current tip-tilt correction. Because of the limited size of the ATs (1.8m diameter), a low-order system will be sufficient. The goal is to concentrate the energy into a coherent core and to make the encircled energy (into the single mode fibers) stable and less dependent on the atmospheric conditions in order to increase the sensitivity of the interferometric instruments. The system will use the ESO real time computer platform Sparta-light as the baseline. This paper presents the preliminary design concept and outlines the benefits to current and future VLTI instruments.

ELMER is a multi-purpose instrument for the GTC designed for both, Imaging and Spectrosopy in the visible range. The CCD camera employs a E2V Technologies CCD44-82 detector mounted in a high performance LN2 Bath Cryostat based on an ESO design and a SDSU-II CCD controller with parallel interface. The design including the low-noise fan-out electronics has been kept flexible to allow alternatively the use of MIT/LL CCID-20 detectors. We present the design of the CCD camera and data acquisition system and first performance test results.

The scientific instrument ELMER for the GTC 10-m telescope integrates an E2V Technologies CCD44-82 detector and can optionally use the MIT/LL CCID-20 device. Fan-out electronics have been developed that support both detectors reusing the same PCB design and cabling. The main system component, the fan-out board, provides dual-channel input clamp and preamplification of the CCD output signal as well as filtering and active ESD protection of all the CCD lines within a 60x80mm envelope. The preamplifier stage is based on complementary bipolar operational amplifiers with dielectric isolation technology for optimum noise performance and minimum settling time. Matched, discrete JFET buffers are used for improved DC precision. Preliminary tests performed on the system yield 2.0μV rms preamplifier noise after CDS at 50kHz readout frequency. Slew rate in excess of 230V/μs and settling time well below 75ns have been obtained for a gain 4 preamplifier configuration driving non terminated coaxial cable.

The GTC Acquisition Cameras and Wavefront Sensors are based on a modular design with remote, low-profile and lightweight CCD heads and a compact CCD controller. The cameras employ E2V Technologies Peltier cooled CCD47-20 and CCD39-01 detectors, which achieve 1Hz and 200Hz full frame readouts, respectively. The CCD controller is a modified version of the Magellan CCD controller (Greg Burley - OCIW), which is linked to the GTC control system. We present the detailed design and first performance results of the cameras.