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With the upgrade from GRAVITY to GRAVITY$^+$ the instrument will evolve into an all-sky interferometer that can observe faint targets, such as high redshift AGN. Observing the faintest targets requires reducing the noise sources in GRAVITY as much as possible. The dominant noise source, especially in the blue part of the spectrum, is the backscattering of the metrology laser light onto the detector. To reduce this noise we introduce two new metrology modes. With a combination of small hardware changes and software adaptations, we can dim the metrology laser during the observation without losing the phase referencing. For single beam targets, we can even turn off the metrology laser for the maximum SNR on the detector. These changes lead to an SNR improvement of over a factor of two averaged over the whole spectrum and up to a factor of eight in the part of the spectrum currently dominated by laser noise., Comment: Proceeding of SPIE Astronomical Telescopes + Instrumentation 2022

In this paper we will give an overview of the status of the three instruments and one adaptive optics module that are currently under construction for the European Southern Observatory (ESO) Extremely Large Telescope (ELT). Currently three of those instruments are in the final design stages and the adaptive optics module, MAORY, is rapidly approaching its Preliminary Design Review (PDR). Funding for the laser tomographic module for HARMONI has been secured and that module is now included as part of that overall instrument project. The PDR phase of the instruments has strongly highlighted the ambitious nature of these and all 30-m class instrument projects. Scientifically, managerially and technically, the step up from the 8-m class is challenging. This paper will provide an introduction to all these instruments and will highlight some of the important developments required to realise them.

HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument's capabilities from a user perspective, provide a summary of the instrument's design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.

We present the successful demonstration of world's first large-separation ~30" off-axis fringe tracking with four telescopes in October 2019. With this technique we increase the sky-coverage for optical interferometry by orders of magnitude compared to current technology. Following the early work at the Palomar Testbed Interferometer, the first demonstration of off-axis fringe tracking at the Keck Interferometer and with PRIMA at the ESO Very Large Telescope Interferometer, and the breakthrough with the GRAVITY Galactic Center observations, we enhanced the VLTI infrastructure for GRAVITY to take advantage of the PRIMA Star separators and Differential Delay Lines for off-axis fringe tracking. In our presentation we give an introduction to the subject, present the enhancements of the VLTI, and present our results from the first on-sky operation in October 2019, with observations of the Orion Trapezium Cluster, a field brown dwarf, and a high redshift quasar.

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 ESO Extremely Large Telescope (ELT) has been in construction since 2014. In parallel with the construction of the telescope, ESO has entered into agreements with consortia in the ESO member states to build the first instruments for that telescope. To meet the telescope science goals, the ambitious instrument plan includes two instruments for first light: an optical to near-infrared integral field spectrograph with a dedicated adaptive optics system (HARMONI) and a near-infrared camera with simple spectrograph (MICADO) behind a multi-conjugate adaptive optics module (MAORY). The next instrument will be a mid-infrared imager and spectrograph (METIS). Plans to follow this first suite of instruments include a high-resolution spectrograph (HIRES) and a multi-object spectrograph (MOSAIC). Technology development is underway to prepare for building the ELT Planetary Camera and Spectrograph. An overview of the telescope and its instruments is given.

The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Telescope Interferometer was never dimensioned for robust fringe tracking, except when atmospheric seeing conditions are excellent. Increasing the level of wavefront correction at the telescopes is expected to improve the coupling into the single-mode fibres of the instruments, and enable robust fringe tracking even in degraded conditions. We deployed a new adaptive optics module for interferometry (NAOMI) on the Auxiliary Telescopes. We present its design, performance, and effect on the observations that are carried out with the interferometric instruments., Comment: 10 pages, 18 figures, 2 tables, A&A forthcoming

The Very Large Telescope Interferometer Auxiliary Telescopes will soon be equipped with an adaptive optics system called NAOMI. The corrective optics deformable mirror is the commercial DM241 from ALPAO. Being part of an interferometer operating from visible to mid-infrared, the DMs of NAOMI face several challenges (high level of reliability, open-loop chopping, piston-free control, WFS/DM pupil rotation, high desired bandwidth and stroke). We here describe our extensive characterization of the DMs through measurements and simulations. We summarize the operational scenario we have defined to handle the specific mirror properties. We conclude that the ALPAO DMs have overall excellent properties that fulfill most of the stringent requirements and that deviations from specifications are easily handled. To our knowledge, NAOMI will be the first astronomical system with a command in true Zernike modes (allowing software rotation), and the first astronomical system in which a chopping is performed with the deformable mirror (5” sky, at 5 Hz).

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.

In the last years the ELT Program has entered construction phase. For the large 39 meter segmented primary mirror unit with thousands of components this means that the start of the series production is getting closer, where the final hardware will be built. The M1 Unit has been broken down in products and a procurement strategy has been developed. Most of the major design decisions have been frozen and component specifications have been settled. Most of the suppliers have already been selected and contracts have been kicked off. This paper describes the ELT M1 Unit product breakdown and the procurement baseline for each product and its status. The production contracts would not have been possible without intense prototyping and verification strategies independent of the component contracts. Therefore, the paper also takes a look back at the prototypes and de-risking strategies, which had been put in place to prepare for construction phase. Ramping up the construction contracts involves finishing design details for some products while setting up production lines for others. This requires controlling interfaces and cross-contract dependencies, a challenge described in this paper. For continuous de-risking similar verification strategies than during the design phase are planned in parallel with the production until telescope assembly, integration and verification. These measures will increase confidence in the design choices, allow early discovery of remaining design flaws and provide training means for assembly and integration long time before all components of the ELT M1 are complete and being installed on Cerro Armazones in Chile. The paper will also give an outlook on these running and planned activities.

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.

The MACAO curvature wavefront sensors have been designed as a generic adaptive optics sensor for the Very Large Telescope. Six systems have been manufactured and implemented on sky: four installed in the UTs Coude train as an AO facility for the VLTI, and two in UT’s instruments, SINFONI and CRIRES. The MACAO-VLTI have now been in use for scientific operation for more than a decade and are planned to be operated for at least ten more years. As second generation instruments for the VLTI were planned to start implementation in end of 2015, accompanied with a major upgrade of the VLTI infrastructure, we saw it as a good time for a rejuvenation project of these systems, correcting the obsolete components. This obsolescence correction also gave us the opportunity to implement improved capabilities: the correction frequency was pushed from 420 Hz to 1050 Hz, and an automatic vibrations compensation algorithm was added. The implementation on the first MACAO was done in October 2014 and the first phase of obsolescence correction was completed in all four MACAO-VLTI systems in October 2015 with the systems delivered back to operation. The resuming of the scientific operation of the VLTI on the UTs in November 2015 allowed to gather statistics in order to evaluate the improvement of the performances through this upgrade. A second phase of obsolescence correction has now been started, together with a global reflection on possible further improvements to secure observations with the VLTI.

GRAVITY is a second generation near-infrared VLTI instrument that will combine the light of the four unit or four auxiliary telescopes of the ESO Paranal observatory in Chile. The major science goals are the observation of objects in close orbit around, or spiraling into the black hole in the Galactic center with unrivaled sensitivity and angular resolution as well as studies of young stellar objects and evolved stars. In order to cancel out the effect of atmospheric turbulence and to be able to see beyond dusty layers, it needs infrared wave-front sensors when operating with the unit telescopes. Therefore GRAVITY consists of the Beam Combiner Instrument (BCI) located in the VLTI laboratory and a wave-front sensor in each unit telescope Coude room, thus aptly named Coude Infrared Adaptive Optics (CIAO). This paper describes the CIAO design, assembly, integration and verification at the Paranal observatory.

MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal., Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2016, 11 pages, 6 Figures

MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument built for ESO (European Southern Observatory). The MUSE project is supported by a European consortium of 7 institutes. After the finalisation of its integration in Europe, the MUSE instrument has been partially dismounted and shipped to the VLT (Very Large Telescope) in Chile. From October 2013 till February 2014, it has then been reassembled, tested and finally installed on the telescope its final home. From there it collects its first photons coming from the outer limit of the visible universe. This critical moment when the instrument finally meets its destiny is the opportunity to look at the overall outcome of the project and the final performance of the instrument on the sky. The instrument which we dreamt of has become reality. Are the dreamt performances there as well? These final instrumental performances are the result of a step by step process of design, manufacturing, assembly, test and integration. Now is also time to review the path opened by the MUSE project. What challenges were faced during those last steps, what strategy, what choices did pay off? What did not?

Instrumentation on Paranal Observatory is currently composed of 18 scientific instruments (operational, in commissioning or in stand by) and 8 technical instruments (test camera, fringe tracking, AO modules, laser guide star facility, tip-tilt sensor). Their implementations and operations started 15 years ago. Over the years enough information to describe their typical behavior was gathered to define a preventive maintenance plan for each instrument and/or a general refurbishment in order to keep their reliability and performance.

MATISSE is the mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This second generation interferometry instrument will open new avenues in the exploration of our Universe. Mid-infrared interferometry with MATISSE will allow significant advances in various fundamental research fields: studies of disks around young stellar objects where planets form and evolve, surface structures and mass loss of stars in late evolutionary stages, and the environments of black holes in active galactic nuclei. MATISSE is a unique instrument. As a first breakthrough it will enlarge the spectral domain used by optical interferometry by offering the L & M bands in addition to the N band, opening a wide wavelength domain, ranging from 2.8 to 13 μm on angular scales of 3 mas (L/M band) / 10 mas (N band). As a second breakthrough, it will allow mid-infrared imaging – closure-phase aperture-synthesis imaging – with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. MATISSE will offer various ranges of spectral resolution between R~30 to ~5000. In this article, we present some of the main science objectives that have driven the instrument design. We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performance and discuss the project status. The operations concept will be detailed in a more specific future article, illustrating the observing templates operating the instrument, the data reduction and analysis, and the image reconstruction software.

The ESO Very Large Telescope Interferometer (VLTI) using the Unit Telescope (UT) was strongly affected by vibrations since the first observations. Investigation by ESO on that subject had started in 2007, with a considerable effort since mid 2008. An important number of investigations on various sub-systems (On telescope: Guiding, Passive supports, Train Coude, insulation of electronics cabinets; On Instruments: dedicated campaign on each instruments with a special attention on the ones equipped with Close Cycle Cooler) were realized. Vibrations were not only recorded and analyzed using the usual accelerometers but also using on use sub-systems as InfRared Image Sensor (IRIS) and Multiple Applications Curvature Adaptive Optics (MACAO) and using a specific tool developed for vibrations measurements Mirror vibrAtion Metrology systeM for the Unit Telescope (MAMMUT). Those tools and systems have been used in order to improve the knowledge on telescope by finding sources. The sources whenever it was possible were damped. As known for years, instruments are still the principal sources of vibrations, for the majority of the UT. A special test in which 2 UTs instruments were completely shut down was realized to determine the minimum Optical Path Length (OPL) achievable. Vibrations is now a part of the instruments interface document and during the installation of any new instrument (KMOS) or system (AOF) a test campaign is realized. As a result some modifications (damping of CCC) can be asked in case of non-compliance. To ensure good operational conditions, levels of vibrations are regularly recorded to control any environmental change.

Two algorithms were recently studied for C 2 n profiling from wide-field Adaptive Optics (AO) measurements on GeMS (Gemini Multi-Conjugate AO system). They both rely on the Slope Detection and Ranging (SLODAR) approach, using spatial covariances of the measurements issued from various wavefront sensors. The first algorithm estimates the C 2 n profile by applying the truncated least-squares inverse of a matrix modeling the response of slopes covariances to various turbulent layer heights. In the second method, the profile is estimated by deconvolution of these spatial cross-covariances of slopes. We compare these methods in the new configuration of ESO Adaptive Optics Facility (AOF), a high-order multiple laser system under integration. For this, we use measurements simulated by the AO cluster of ESO. The impact of the measurement noise and of the outer scale of the atmospheric turbulence is analyzed. The important influence of the outer scale on the results leads to the development of a new step for outer scale fitting included in each algorithm. This increases the reliability and robustness of the turbulence strength and profile estimations.

MUSE (Multi Unit Spectroscopic Explorer) is a second generation instrument, built for ESO (European Southern Observatory) and dedicated to the VLT (Very Large Telescope). This instrument is an innovative integral field spectrograph (1x1 arcmin 2 Field of View), operating in the visible wavelength range, from 465 nm to 930 nm. The MUSE project is supported by a European consortium of 7 institutes. After the finalisation of its integration and test in Europe validated by its Preliminary Acceptance in Europe, the MUSE instrument has been partially dismounted and shipped to the VLT (Very Large Telescope) in Chile. From October 2013 till February 2014, it has then been reassembled, tested and finally installed on the telescope its final home. From there it will collect its first photons coming from the outer limit of the visible universe. To come to this achievement, many tasks had to be completed and challenges overcome. These last steps in the project life have certainly been ones of the most critical. Critical in terms of risk, of working conditions, of operational constrains, of schedule and finally critical in terms of outcome: The first light and the final performances of the instrument on the sky.

We present a new Adaptive Phase Mask (APM) coronagraph design enabling Amplitude and Phase Modulation control (APM). The Adaptive Phase mask coronagraph is a technique proposed to provide both high dynamic and high angular resolution imaging of faint sources around bright objects. Discriminating faint sources from static speckles is a challenging problem. Our new system is based on synchronous demodulation that allows high dynamic range detection of a faint target immersed in a background. The APM^2 uses the coherence of speckles to discriminate them from proper companions, using the mask itself as the electric field modulator. Synchronous detection in the radio frequency range is used to side-step the effect of atmospheric turbulence and enable the detection of low amplitude signals. The APM^2 concept offers high dynamic range detection and provides a time- and cost-effective method to quantify the probability of presence of a faint object close to the central star.

In November 2012, we installed an L-band annular groove phase mask (AGPM) vector vortex coronagraph (VVC) inside NACO, the adaptive optics camera of ESO’s Very Large Telescope. The mask, made out of diamond subwavelength gratings has been commissioned, science qualified, and is now offered to the community. Here we report ground-breaking on-sky performance levels in terms of contrast, inner working angle, and discovery space. This new practical demonstration of the VVC, coming a few years after Palomar’s and recent record-breaking lab experiments in the visible (E. Serabyn et al. 2013, these proceedings), shows once again that this new-generation coronagraph has reached a high level of maturity.

Context. High contrast imaging has thoroughly combed through the limited search space accessible with first-generation ground-based adaptive optics instruments and the Hubble Space Telescope. Only a few objects were discovered, and many non-detections reported and statistically interpreted. The field is now in need of a technological breakthrough. Aim. Our aim is to open a new search space with first-generation systems such as NACO at the Very Large Telescope, by providing ground-breaking inner working angle (IWA) capabilities in the L' band. The L' band is a sweet spot for high contrast coronagraphy since the planet-to-star brightness ratio is favorable, while the Strehl ratio is naturally higher. Methods. An annular groove phase mask (AGPM) vector vortex coronagraph optimized for the L' band, made from diamond subwavelength gratings was manufactured and qualified in the lab. The AGPM enables high contrast imaging at very small IWA, potentially being the key to unexplored discovery space. Results. Here we present the installation and successful on-sky tests of an L'-band AGPM coronagraph on NACO. Using angular differential imaging, which is well suited to the rotational symmetry of the AGPM, we demonstrated a \Delta L' > 7.5 mag contrast from an IWA ~ 0".09 onwards, during average seeing conditions, and for total integration times of a few hundred seconds., Comment: 4 pages, 4 figures

We present the concept of an instrument that will create 4 circular sub-pupils of 3 m in diameter. Each sub-pupil path will be corrected by a high order adaptive optics system (SR~80% in H) without spider and M2 obstruction. These four independent channels, obviously all pointed towards the same field, allows the possibility of covering totally different parts of the electromagnetic spectrum simultaneously without compromising Signal to Noise Ratio. Each channel can be dedicated to very specialized but complementary purposes: high contrast imaging, pseudo-wide field imaging, high precision multi-color photometry, medium-resolution spectroscopy, polarimetry and sparse-aperture masking.

A dual coronagraph based on the Adaptive Mask concept is presented in this paper. A Lyot coronagraph with a variable diameter occulting disk and a nulling stellar coronagraph based on the Adaptive Phase Mask concept using polarization interferometry are presented in this work. Observations on sky and numerical simulations show the usefulness of the proposed method to optimize the nulling efficiency of the coronagraphs. In the case of the phase mask, the active control system will correct for the detrimental effects of image instabilities on the destructive interference (low-order aberrations such as tip-tilt and focus). The phase mask adaptability both in size, phase and amplitude also compensate for manufacturing errors of the mask itself, and potentially for chromatic effects. Liquid-crystal properties are used to provide variable transmission of an annulus around the phase mask, but also to achieve the achromatic π phase shift in the core of the PSF by rotating the polarization by 180°.A compressed mercury (Hg) drop is used as an occulting disk for the Lyot mask, its size control offers an adaptation to the seeing conditions and provides an optimization of the Tip-tilt correction.

The analysis of the laser behavior on sky and of the adaptive optics system of SINFONI is made systematically since a year. This campaign of measurements will continue during the first semester 2012. The analysis, the results and the proposed optimization will be presented in this proceeding.

We will present the status of the scientific instruments and their associated systems at the Paranal observatory and the approach used to integrate, commission and to keep them at their maximum performances.

MATISSE is a mid-infrared spectro-interferometer combining the beams of up to four Unit Telescopes or Auxiliary Telescopes of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. New characteristics present in MATISSE will give access to the mapping and the distribution of the material, the gas and essentially the dust, in the circumstellar environments by using the mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient uv-coverage: 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime. We give an overview of the instrument including the expected performances and a view of the Science Case. We present how the instrument would be operated. The project involves the collaborations of several agencies and institutes: the Observatoire de la Cote d’Azur of Nice and the INSU-CNRS in Paris, the Max Planck Institut fur Astronomie of Heidelberg; the University of Leiden and the NOVA-ASTRON Institute of Dwingeloo, the Max Planck Institut fur Radioastronomie of Bonn, the Institut fur Theoretische Physik und Astrophysik of Kiel, the Vienna University and the Konkoly Observatory.

New optical phasing sensor technologies have been studied with a test bench experiment, called Active Phasing Experiment, on-sky at the European Southern Observatory Very Large Telescope. One of the sensors was of the Shack–Hartmann type using cylindrical lenslets across the segment borders for the measurement of the phasing errors. With bright stars, the precision of the measurement of piston steps at a single border was better than 9 nm wavefront RMS, and the precision of the closed-loop correction of the piston errors of the segments across the whole mirror was better than 10 nm wavefront RMS. With dimmer stars of magnitude up to 14.5, precisions of the order of 22 nm wavefront RMS were obtained.

International audience; The Active Phasing Experiment (APE) was designed to test four different phasing techniques and to validate wavefront control concepts for Extremely Large Telescopes. One of the sensors is the ZErnike Unit for Segment phasing (ZEUS), which was successfully tested on-sky along with the rest of the APE experiment at one of the Nasmyth platforms of the Very Large Telescope (VLT) in 2009. During the four observing campaigns, multiple results were obtained in open-loop and in closed-loop at different wavelengths. We present in this paper an analysis of the multi-wavelength data in terms of piston measurement precision at the edges of the segments and on the reconstructed wavefront, and an analysis of the evolution of these errors in successive closed-loop runs at different wavelengths. This work demonstrates how the applied multi-wavelength algorithm leads to convergence, allowing phasing of segments with piston errors of several microns.

GRAVITY is an adaptive optics assisted Beam Combiner for the second generation VLTI instrumentation. The instrument will provide high-precision narrow-angle astrometry and phase-referenced interferometric imaging in the astronomical K-band for faint objects. We describe the wide range of science that will be tackled with this instrument, highlighting the unique capabilities of the VLTI in combination with GRAVITY. The most prominent goal is to observe highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at center of the Milky Way. We present the preliminary design that fulfils the requirements that follow from the key science drivers: It includes an integrated optics, 4-telescope, dual feed beam combiner operated in a cryogenic vessel; near-infrared wavefrontsensing adaptive optics; fringe-tracking on secondary sources within the field of view of the VLTI and a novel metrology concept. Simulations show that 10 {\mu}as astrometry within few minutes is feasible for a source with a magnitude of mK = 15 like Sgr A*, given the availability of suitable phase reference sources (mK = 10). Using the same setup, imaging of mK = 18 stellar sources in the interferometric field of view is possible, assuming a full night of observations and the corresponding UV coverage of the VLTI., Comment: 20 pages, Proceedings SPIE Astronomical Telescopes and Instrumentation Conference 2010

The primary mirror of the future European Extremely Large Telescope will be equipped with 984 hexagonal segments. The alignment of the segments in piston, tip, and tilt within a few nanometers requires an optical phasing sensor. A test bench has been designed to study four different optical phasing sensor technologies. The core element of the test bench is an active segmented mirror composed of 61 flat hexagonal segments with a size of 17 mm side to side. Each of them can be controlled in piston, tip, and tilt by three piezoactuators with a precision better than 1 nm. The context of this development, the requirements, the design, and the integration of this system are explained. The first results on the final precision obtained in closed-loop control are also presented.

We present a noncontact optical metrology measuring the pistons and tip/tilt angles of the 61 hexagonal segments of a compact-sized segmented mirror. The instrument has been developed within the scope of a design study for the European Extremely Large Telescope (E-ELT). It is used as reference sensor for cophasing of the mirror segments in closed-loop control. The mirror shape is also measured by different types of stellar light-based phasing cameras whose performances will be evaluated with regard to a future E-ELT. Following a description of the system architecture, the second part of the paper presents experimental results demonstrating the achieved precision: 0.48 nm rms in piston and 74 nrad rms in tip/tilt.

The Shack-Hartmann Phasing Sensor (SHAPS) has been integrated in the Active Phasing Experiment (APE) at ESO. It is currently under test in the laboratory. The tests on sky are foreseen for the end of 2008, when APE will be mounted at the Nasmyth focus of one of the VLT unit telescopes. SHAPS is based on the Shack-Hartmann principle: the lenslet array is located in a plane which is optically conjugated to the Active Segmented Mirror (ASM) of APE and is composed of two types of microlenses, circular and cylindrical, which give information about the wavefront slope and the piston steps, respectively. This proceeding contains a description of SHAPS and of the algorithms implemented for the wavefront reconstruction and for the phasing. The preliminary results obtained during the laboratory tests are discussed and compared with the theoretical predictions. The performances of SHAPS at the VLT and at the European Extremely Large Telescope (E-ELT) are estimated.

The construction of extremely large telescope is only possible with a segmented primary mirror. The phasing of the primary mirror due to its size and its number of segments is a main concern at the European Southern Observatory. The European Southern Observatory has developed a test bench called Active Phasing Experiment to study new phasing technology and new telescope control system. The key subsystem of this experiment is a scaled down Active Segmented Mirror (ASM) composed of sixty-one hexagonal segments of seventeen millimeters side to side. Each hexagonal mirror can all be controlled in piston, tip and tilt. The integration of this jewel piece of opto-mechanic started after the successful results obtained with the manufacturing of a prototype composed of only seven modules.

International audience; In the framework of the Active Phasing Experiment (APE), four different phasing techniques are tested. The ZErnike Unit for Segment phasing sensor (ZEUS) is integrated on the APE bench. APE has been tested in the laboratory before it will be installed on one of the Nasmyth platform of a Very Large Telescope (VLT) Unit Telescope to perform on sky tests. The ZEUS phasing sensor concept has its origins in the Mach-Zehnder interferometer equipped with a spatial filter in its focal plane. In this paper, the ZEUS phasing sensor is described together with its theoretical background and deployment within the APE experiment. The algorithms and its elements used to reconstruct the wavefront are described. Finally, the preliminary results obtained in the laboratory are presented.

International audience; The purpose of the Active Phasing Experiment, designed under the lead of ESO, is to study new phasing technologies and to validate wavefront control concepts for Extremely Large Telescopes. The Active Phasing Experiment is currently tested in the laboratory at the ESO headquarters and will be tested on sky at a Nasmyth focus of a VLT unit telescope at the end of 2008. The test bench contains four different phasing sensors which are tested in parallel to compare them under the same conditions. They have been developed by Istituto Nazionale di Astrofisica in Florenze, Instituto Astrofisica Canarias in Tenerife, Laboratoire d'Astrophysique de Marseille and ESO. It includes also an Active Segmented Mirror which simulates the segmentation of a primary mirror. A non-contact optical metrology has been developed by Fogale Nanotech to control it. The VLT focus and the VLT atmospheric conditions are simulated in the laboratory with a turbulence generator producing a seeing between 0.45 and 0.85 arcsec. Once installed on a VLT unit telescope, the control system of the Active Phasing Experiment will be able to control the phasing of the ASM, but also the guiding and the active optics of the VLT. This proceeding gives a brief summary of the opto-mechanical aspects of the Active Phasing experiment, describes its control system and gives an analysis of the preliminary results obtained in the laboratory.

The purpose of the Active Phasing Experiment, designed at ESO, is to validate wavefront control concepts for ELT class telescopes. This instrument includes an Active Segmented Mirror, located in a pupil image. It will be mounted at a Nasmyth focus of one of the unit telescopes of the ESO VLT. The Active Phasing Experiment will compare four types of phasing sensor. One of them is based on the Shack-Hartmann principle. The lenslets in the array will be placed on intersegment borders for the measurement of piston steps, as well and inside the subapertures defined by the segments for the measurement of local slopes generated by the segments and the telescope optics. The paper describes the design of the sensor optics and the lenslet array, and discusses the expected performance of the sensor under laboratory conditions and in the telescope.

This paper presents a non-contact, optical metrology system that allows to measure the pistons and tip/tilt angles of a compact-sized, flat segmented mirror, with nanometer resolution, from a long working distance of a few meters. The system is developed in the scope of the APE project (Active Phasing Experiment), and will be installed on the Very Large Telescope (VLT). It will serve for two purposes: (1) as the sensor within the closed loop control of the mirror segments, and (2) as internal reference metrology to qualify the accuracy of different types of phasing cameras that will be developed and tested within the scope of the APE project. The sensor is based on the concept on instantaneous phase shifting, low-coherence, dual wavelength interferometry. By simultaneously acquiring four interferograms at phase shifts of 90° the system is inherently very insensitive to vibrations. Working at two wavelengths allows absolute distance measurements within the range of half the synthetic wavelength, i.e. in our case within a range of about 25 μm. The concept of low coherence interferometry avoids phase contributions of parasitic reflections and speckle effects. The low coherent light sources are two superluminescent diodes emitting at visible (red) wavelengths with coherence lengths in the range of 25 μm that can be increased by spectral filtering. Dual wavelengths measurements are performed at a rate of 20 Hz. The targeted accuracy is better than 5 nm rms (wavefront). The paper starts with a description of the system architecture. The different subsystems (light source, interferometer core with phase modulator and signal decoder, computer) are discussed. After having presented the optical design, the paper provides a closer look to the measurement and calibration algorithms. Finally, the paper presents the experimental setup and the "first fringes" obtained in the laboratory.

In a framework of ELT design study our group is building an Active Phasing Experiment (APE), the main goals of which is to demonstrate the non-adaptive wavefront control scheme and technology for Extremely Large Telescope (ELT). The experiment includes verification and test of different phasing sensors and integration of a phasing wavefront sensor into a global scheme of segmented telescope active control. After a sufficient number of tests in the laboratory APE will be mounted and tested on sky at a Nasmyth focus of a VLT unit telescope. The paper presents APE as a demonstrator of particular aspects of ELT and provides a general understanding concerning the strategy of segmented mirrors active control.

The Active Segmented Mirror is a key subsystem of the Active Phasing Experiment. The size of the ASM is 154 mm in diameter. It will be used to test new types of phasing sensors recently developed within the ELT design study supported by the European Union. To our knowledge it is the first time that such miniature active optics composed of hexagonal segments having 3 degrees of freedom with a resolution of the order of a few nanometers and a range of several micrometers is manufactured. The ASM is composed of 61 hexagonal segments called "modules". Each module is assembled, glued and integrated from standard (piezo-actuators) and custom-made (mirrors, mechanics) parts procured from industries. The ASM has been designed and integrated at the European Southern Observatory. Specifications, designs, assembly tools, hand work skills, electronics, software, control algorithms and test procedures are the field of competences required to obtain in the end a "plug and play" product. The concept of the ASM is tested and validated by a prototype version composed of 7 modules equivalent of the central area of the ASM itself. The design, integration and results of the ASM tests are presented.

The purpose of the Active Phasing Experiment, designed under the lead of ESO, is to validate wavefront control concepts for ELT class telescopes. This instrument includes an Active Segmented Mirror, located in a pupil image. It will be mounted at a Nasmyth focus of one of the Unit Telescopes of the ESO VLT. APE contains four different types of phasing sensors, which are developed by Istituto Nazionale di Astrofisica in Arcetri, Instituto Astrofisica Canarias, Laboratoire d'Astrophysique de Marseille and ESO. These phasing sensors can be compared simultaneously under identical optical and environmental conditions. All sensors receive telecentric F/15 beams with identical optical quality and intensity. Each phasing sensor can measure segmentation errors of the active segmented mirror and correct them in closed loop. The phasing process is supervised by an Internal Metrology system developed by FOGALE Nanotech and capable of measuring piston steps with an accuracy of a few nanometers. The Active Phasing Experiment is equipped with a turbulence generator to simulate atmospheric seeing between 0.45 and 0.85 arcsec in the laboratory. In addition, the Active Phasing Experiment is designed to control simultaneously with the phasing corrections the guiding and the active optics of one of the VLT Unit Telescopes. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract No 011863).

The Very Large Telescope Interferometer (VLTI)1 that coherently combines the four VLT 8.2-m Unit Telescopes (UT's) is on the point to be fully equipped with its dedicated array of Auxiliary Telescopes (AT's). This array includes four 1.8-m telescopes which can be relocated on thirty observing stations distributed on the top of the Paranal Observatory. This array, albeit less sensitive than the array of UT's, is a key element for the scientific operation of the VLTI. Indeed, it will provide the best imaging capability thanks to the many possible baselines (up to 200m), it will be used for the Narrow Angle Astrometry mode which requires long term monitoring and the longest baselines not accessible with the UT's, and it will enable full-time use of the VLTI facilities even when the UT's are used for stand-alone observation. The Auxiliary Telescopes have been designed, manufactured and tested in Europe by the company AMOS (Belgium) under ESO contract. After acceptance in Europe, ESO takes over the responsibility for the transport to Paranal, reassembly and final commissioning. Currently the first three AT's have been put into operation on Paranal while the fourth one is scheduled to arrive at the observatory in August 2006. This paper presents the actual performances of the Auxiliary Telescopes, as measured during the commissioning of the first three AT's. An emphasis is given to the requirements dictated by the interferometer needs, including the ease and accuracy with which the telescopes can be relocated, the excellent image quality, and the nanometer-level stability for Optical Path Length.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The future European Extremely Large Telescope will be composed of one or two giant segmented mirrors (up to 100 m of diameter) and of several large monolithic mirrors (up to 8 m in diameter). To limit the aberrations due to misalignments and defective surface quality it is necessary to have a proper active optics system. This active optics system must include a phasing system to limit the degradation of the PSF due to misphasing of the segmented mirrors. We will present the lastest design and development of the Active Phasing Experiment that will be tested in laboratory and on-sky connected to a VLT at Paranal in Chile. It includes an active segmented mirror, a static piston plate to simulate a secondary segmented mirror and of four phasing wavefront sensors to measure the piston, tip and tilt of the segments and the aberrations of the VLT. The four phasing sensors are the Diffraction Image Phase Sensing Instrument developed by Instituto de Astrofisica de Canarias, the Pyramid Phasing Sensor developed by Arcetri Astrophysical Observatory, the Shack-Hartmann Phasing Sensor developed by the European Southern Observatory and the Zernike Unit for Segment phasing developed by Laboratoire d'Astrophysique de Marseille. A reference measurement of the segmented mirror is made by an internal metrology developed by Fogale Nanotech. The control system of Active Phasing Experiment will perform the phasing of the segments, the guiding of the VLT and the active optics of the VLT. These activities are included in the Framework Programme 6 of the European Union.

Here we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond subwavelength gratings tuned to the L' band. The vector vortex coronagraph enables high contrast imaging at very small inner working angle (here 0″.09, the diffraction limit of the VLT at L'), potentially being the key to a new parameter space. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star (Mawet et al. 2013), and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 AU. The circumstellar disk was also resolved from ≃ 1″ to 5″ (see J. Milli et al., these proceedings). These results showcase the potential of the NACO L-band AGPM over a wide range of spatial scales.

The Multi-Atmospheric Phase screens and Stars (MAPS) instrument is a powerful tool that has been developed in the framework of the ESO Multi-conjugate Adaptive optics Demonstrator project (MAD). It allows emulating a 3D evolving Paranal-like atmosphere as well as up to 12 sources in a 2 arc minutes field of view, as seen at a Nasmyth focus of one of the VLT. It will be used to perform advanced laboratory tests on MAD before its shipment to Chile. In this paper we present the opto-mechanical design of MAPS. This one simulates the characteristics of the VLT focus and achieves a high Strehl Ratio over the whole Field of View in the visible as well as in the infrared. A curved entrance plate crowded with fibers emulates various stars configurations including real sky asterisms. In order to simulate the atmosphere, three rotating Phase Screens are placed in the beam and conjugated with different altitudes. Those are glass plates dig in their surface in a way that the beam passing through is distorted as it would be by an atmospheric turbulent layer. In this poster we also present the process of research that lead to the choice of a reliable technique to imprint the aberrations into the screens, their properties and expected performance.

The point spread function of a segmented aperture is seriously affected by the misalignment of the segments. Stringent requirements apply to position sensors and their calibration. The Active Phasing Experiment (APE) will be a technical instrument aimed at testing possible phasing techniques for a European Giant Optical Telescope (EGOT) in a representative environment. It will also integrate simultaneous control of segmented and monolithic, active surfaces. A mirror composed of 61 hexagonal segments is conjugated to the primary mirror of the VLT. Each segment can be moved in piston, tip and tilt and can be controlled in open or closed loop. Three new types of Phasing Wave Front Sensors dedicated to the measurement of segmentation errors will be tested, evaluated and compared: a modified Mach-Zehnder sensor developed by the LAM and ESO, a Pyramid Sensor developed by Arcetri, and a Curvature Sensor developed by IAC. A reference metrology developed by FOGALE will be added to measure directly the deformation of the segmented mirror and check the efficiency of the tested wavefront sensors. This metrology will be based on a synthetic wavelength instantaneous phase stepping method. This experiment will first run in the laboratory with point-like polychromatic sources and a turbulence generator. In a second step, it will be mounted at a Nasmyth focus of a VLT unit telescope. These activities are included in a proposal to the European Commission for funding within Framework Program 6.

Progress in the conceptual design phase of ESO's OWL 100-m optical and near-infrared telescope is reported, with emphasis on the development of the science case. The Phase A opto-mechanical design is now basically completed, and provides a clean, symmetrical geometry of the pupil, with a near-circular outer edge. We also report about the latest outcome of industrial studies, introduce the essential definition of the wavefront control systems, and outline operational concepts and instruments priorities. Finally, we elaborate on the favorable cost factors associated to the telescope design, its compatibility with low industrial risks, and argue that progressive implementation allows for competitive timescales. In particular, we show that suitable fabrication and integration schemes should accommodate for a start of science operation at unequalled potential and within a time frame comparable to that of smaller designs, while at the same time maximizing R&D time for critical subsystems.