The ELT prefocal stations provide wavefront sensing to support the active control of the telescope during observations; they also include mirrors to distribute the telescope optical beam to the scientific instrument or diagnostic tool that finally uses the light collected by the ELT. Built in to the prefocal stations is a hosted metrology positioning system where metrology measuring instruments including a laser tracker and alignment telescope will be installed. This metrology will be used during coarse alignment of the ELT, to maintain the internal alignment of the prefocal stations, and to locate them with respect to their surroundings. The detailed design and application of these instruments is described here, together with a first set of test results.
Presently TNO/Demcon are manufacturing nine Laser Projection Systems (LPS). TNO is responsible for the design and manufacturing of the Optical Tube Assembly (OTA), the baseplate and the LPS cover. Demcon designed and manufactured the Beam Conditioning and Diagnostic System (BCDS). TNO is also responsible for the system performance and its verification tests.
Six units will be used on the ELT. The other three are destined for the VLT. That will allow the operation of the adaptive mirrors enabling unprecedented image quality of the telescopes. The design of this system is based on the four laser guide stars units as used on the VLT.
The system has been upgraded considerably compared to the units used for the VLT. Its FOV has increased to 7 arcmin (half cone). The laser power goes up to 50W and the BCDS has been completely redesigned. The BCDS is located between the laser source and the OTA that produces the Ø300 mm output beam. Maintainability and accessibility of the system have also been much improved.
Prime qualities are its insensitivity to temperature changes (static and dynamic), its accuracy and its FOV. Assembly of the first unit is finished and in January the acceptance testing of the system started. The first unit is expected to be delivered to ESO in autumn 2024.
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 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) 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 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.
GALACSI is the Adaptive Optics (AO) module that will serve the MUSE Integral Field Spectrograph. In Wide Field Mode it will enhance the collected energy in a 0.2”×0.2” pixel by a factor 2 at 750 nm over a Field of View (FoV) of 1’×1’ using the Ground Layer AO (GLAO) technique. In Narrow Field Mode, it will provide a Strehl Ratio of 5% (goal 10%) at 650 nm, but in a smaller FoV (7.5”×7.5” FoV), using Laser Tomography AO (LTAO). Before being ready for shipping to Paranal, the system has gone through an extensive testing phase in Europe, first in standalone mode and then in closed loop with the DSM in Europe. After outlining the technical features of the system, we describe here the first part of that testing phase and the integration with the AOF ASSIST (Adaptive Secondary Setup and Instrument Stimulator) testbench, including a specific adapter for the IRLOS truth sensor. The procedures for the standalone verification of the main system performances are outlined, and the results of the internal functional tests of GALACSI after full integration and alignment on ASSIST are presented.
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 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.
We present the latest update of the European Southern Observatory's Very Large Telescope interferometer (VLTI). The operations of VLTI have greatly improved in the past years: reduction of the execution time; better offering of telescopes configurations; improvements on AMBER limiting magnitudes; study of polarization effects and control for single mode fibres; fringe tracking real time data, etc. We present some of these improvements and also quantify the operational improvements using a performance metric. We take the opportunity of the first decade of operations to reflect on the VLTI community which is analyzed quantitatively and qualitatively. Finally, we present briefly the preparatory work for the arrival of the second generation instruments GRAVITY and MATISSE.
The New Adaptive Optics Module for Interferometry (NAOMI) 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 ATs are designed for interferometry which they are essentially dedicated for. The project goal is to equip the telescopes with a low-order Shack-Hartmann system operating in the visible in place of the current tip-tilt correction. The deformable mirror (DM) for NAOMI is rotating with the AT azimuth axis whereas the wavefront sensor (WFS), which signals are used to control the DM, has a fixed position in the telescope basement. It is not co-rotating with the DM. The result is that the projection of the actuator pattern is rotating with respect to the WFS when the telescope is tracking an object on sky. In order to avoid the use of an optical de-rotator we developed an algorithm to de-rotate the commands to the DM in software. This paper outlines the concept of the software de-rotation as well as the performance obtained from end-to-end simulations.
GALACSI is the Adaptive Optics (AO) modules of the ESO Adaptive Optics Facility (AOF) that will correct the wavefront delivered to the MUSE Integral Field Spectrograph. It will sense with four 40×40 subapertures Shack-Hartmann wavefront sensors the AOF 4 Laser Guide Stars (LGS), acting on the 1170 voice-coils actuators of the Deformable Secondary Mirror (DSM). GALACSI has two operating modes: in Wide Field Mode (WFM), with the four LGS at 64” off axis, the collected energy in a 0.2”×0.2” pixel will be enhanced by a factor 2 at 750 nm over a Field of View (FoV) of 1’×1’ using the Ground Layer AO (GLAO) technique. The other mode, the Narrow Field Mode (NFM), provides an enhanced wavefront correction (Strehl Ratio (SR) of 5% (goal 10%) at 650 nm) but in a smaller FoV (7.5”×7.5”), using Laser Tomography AO (LTAO), with the 4 LGS located closer, at 10” off axis. Before being shipped to Paranal, GALACSI will be first integrated and fully tested in stand-alone, and then moved to a dedicated AOF facility to be tested with the DSM in Europe. At present the module is fully assembled, its main functionalities have been implemented and verified, and AO system tests with the DSM are starting. We present here the main system features and the results of the internal functional tests of GALACSI.
In an AO system the correction to be applied to the Deformable Mirror is computed at each loop cycle from the residual
slopes on the Wavefront Sensor and the Interaction Matrix of the system DM/WFS.
But the a posteriori analysis of the DM commands and WFS slopes can also provide a wealth of information on the
closed loop behavior. In this paper we present a non-exhaustive list of what can be learned from such data. We base our
analysis on simulated data, on data recorded on ESO’s PEACE test bench, and on data recorded on the NAOS instrument
at the VLT during technical nights in 2010 and 2011, in the framework of the preparation of the algorithms for the AO
Facility.
The topics presented include the reconstruction of the input turbulence in the WFS domain (pseudo open-loop slopes),
the estimation of the seeing, turbulence profile, coherence time, wind speed and direction, the measurement of LGS spot
size, the detection of vibrations via modal transfer functions, the identification of DM/WFS mis-registration and the
optimal loop gain computation.
ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets
direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas
giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The
segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the
detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the
overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and
post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the
concepts for common path and diffraction suppression system is presented. The performance of the instrument is
predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through
the various optical elements.
Extreme adaptive optics systems (XAO) dedicated to the search for extrasolar planets are currently being developed for
8-10 meter telescopes. The High-Order Test bench (HOT) is a
high-contrast imaging adaptive optics bench developed at
the European Southern Observatory to test and optimize different techniques and technologies (e.g. wavefront sensors,
coronagraphs, speckle calibration methods, image post-processing). It reproduces realistic conditions at a telescope (e.g.
Very Large Telescope, VLT), including a turbulence generator, a
high-order adaptive optics system, a near-IR
coronagraph, and sequential differential imaging modes (spectral and polarimetric). We discuss the results of XAO
coronagraphy obtained in the laboratory in the context of imminent planet-finder instruments (e.g. SPHERE1, GPI2, and
HiCIAO3). In particular, results obtained with HOT will be discussed and compared with contrast goals of the near-IR
camera of SPHERE.
The purpose of FFREE - the new optical bench devoted to experiments on high-contrast imaging at LAOG - consists in
the validation of algorithms based on off-line calibration techniques and adaptive optics (AO) respectively for the
wavefront measurement and its compensation. The aim is the rejection of the static speckles pattern arising in a focal
plane after a diffraction suppression system (based on apodization or coronagraphy) by wavefront pre-compensation. To
this aim, FFREE has been optimized to minimize Fresnel propagation over a large near infrared (NIR) bandwidth in a
way allowing efficient rejection up to the AO control radius, it stands then as a demonstrator for the future
implementation of the optics that will be common to the scientific instrumentation installed on EPICS.
Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and
explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based
telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the discovery space
towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. EPICS is a
proposed instrument for the European ELT, dedicated to the detection and characterization of Exoplanets by direct
imaging, spectroscopy and polarimetry. ESO completed a phase-A study for EPICS with a large European consortium
which - by simulations and demonstration experiments - investigated state-of-the-art diffraction and speckle suppression
techniques to deliver highest contrasts. The paper presents the instrument concept and analysis as well as its main
innovations and science capabilities. EPICS is capable of discovering hundreds of giant planets, and dozens of lower
mass planets down to the rocky planets domain.
The High Order Testbench (HOT) is a joint experiment of ESO, Durham University and Arcetri Observatory to
built and test in laboratory the performance of Shack-Hartmann and pyramid sensor in a high-order correction
loop using a 32x32 actuators MEMS DM. This paper will describe the pyramid wavefront sensor unit developed
in Arcetri and now installed in the HOT bench at ESO premises. In the first part of this paper we will describe
the pyramid wavefront sensor opto-mechanics and its real-time computer realized with a commercial Linux-PC.
In the second part we will show the sensor integration and alignment in the HOT bench and the experimental
results obtained at ESO labs. Particular attention will be paid to the implementation of the modal control
strategy, like modal basis definition, orthogonalization on the real pupil, and control of edge actuators. A stable
closed loop controlling up to 667 modes has been achieved obtaining a Strehl ratio of 90 -- 93% in H band.
We report laboratory development of coronagraphic devices to be implemented on the High Order Testbench (HOT) to
assess intensity reduction between them at a high Strehl ratio regime. The high order test bench implements extreme
adaptive optics with realistic telescope conditions reproduced by star and turbulence generators. A 32×32 actuator micro
deformable mirror, one pyramid wave front sensor, one Shack-Hartmann wave front sensor and the ESO SPARTA real-time
computer. This will enable characterization and comparative study of different types of coronagraphs in realistic
conditions. We have developed several prototypes of promising coronagraphs concepts: Four Quadrants Phase Mask1
(FQPM), Lyot2 coronagraphs and Apodized Pupil Lyot Coronagraph3 (APLC). We will describe the design of the IR
coronagraphic path on HOT, prototyping processes used for each coronagraph and discuss quality control and first
results obtained on a IR coronagraphic testbench (Strehl ratio ~ 94%). Finally, we will present our experiment plan and
future coronagraph developments.
High-contrast imagers dedicated to the search for extrasolar planets are currently being developed for the VLT
(SPHERE) and Gemini (GPI) observatories. A vital part of such a high-contrast imager is the extreme adaptive optics
(XAO) system that very efficiently removes effects of atmospheric turbulence and instrument aberrations. The high
order test bench (HOT) implements an XAO system under realistic telescope conditions reproduced by star and
turbulence generators. New technological developments (32x32 actuator micro deformable mirror, read-noise free
electron multiplying CCD60, SPARTA real time computer) are used to study and compare two potential XAO wave
front sensors: The Pyramid- and the Shack-Hartmann wave front sensors. We will describe the overall design of HOT
including the sub-systems. We will present the closed loop study results of the behavior of the Shack-Hartmann wave
front sensor in terms of linearity, sensitivity to calibration errors, performance and other specific issues.
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