After the pause imposed by the pandemic, VLTI resumed science operations and restarted technical activities aiming to close commissionings of different modes. While the community develops projects of visiting instruments, the VLTI infrastructure is about to be significantly upgraded with new visible AO and laser guide star systems by the GRAVITY+ project. VLTI operations also evolve, in particular to support imaging programmes, but also towards a more automated and integrated model. In this context, we will present a review of current capabilities, ongoing activities and future plans for the VLTI.
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.
ESO is undertaking a large upgrade of the infrastructure on Cerro Paranal in order to integrate the 2nd generation of interferometric instruments Gravity and MATISSE, and increase its performance. This upgrade started mid 2014 with the construction of a service station for the Auxiliary Telescopes and will end with the implementation of the adaptive optics system for the Auxiliary telescope (NAOMI) in 2018. This upgrade has an impact on the infrastructure of the VLTI, as well as its sub-systems and scientific instruments.
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 μm, 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.
KEYWORDS: Data archive systems, Binary data, Data modeling, Observatories, Calibration, Imaging spectroscopy, Spectroscopy, Spectral calibration, Data processing, Near infrared
The European Southern Observatory Science Archive Facility is evolving from an archive containing predominantly raw data into a resource also offering science-grade data products for immediate analysis and prompt interpretation. New products originate from two different sources. On the one hand Principal Investigators of Public Surveys and other programmes reduce the raw observational data and return their products using the so-called Phase 3 - a process that extends the Data Flow System after proposal submission (Phase 1) and detailed specification of the observations (Phase 2). On the other hand raw data of selected instruments and modes are uniformly processed in-house, independently of the original science goal. Current data products assets in the ESO science archive facility include calibrated images and spectra, as well as catalogues, for a total volume in excess of 16 TB and increasing. Images alone cover more than 4500 square degrees in the NIR bands and 2400 square degrees in the optical bands; over 85000 individually searchable spectra are already available in the spectroscopic data collection. In this paper we review the evolution of the ESO science archive facility content, illustrate the data access by the community, give an overview of the implemented processes and the role of the associated data standard.
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.
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.
Since April 2011, realtime fringe tracking data are recorded simultaneously with data from the VLTI/AMBER interferometric beam combiner. Not only this offers possibilities to post-process AMBER reduced data to obtain more accurate interferometric quantities, it also allows to estimate the performance of the fringe tracking a function of the conditions of seeing, coherence time, flux, etc. First we propose to define fringe tracking performance metrics in the AMBER context, in particular as a function of AMBER’s integration time. The main idea is to determine the optimal exposure time for AMBER: short exposures are dominated by readout noise and fringes in long exposures are completely smeared out. Then we present this performance metrics correlated with Paranal local ASM (Ambient Site Monitor) measurements, such as seeing, coherence time or wind speed for example. Finally, we also present some preliminary results of attempts to model and predict fringe tracking performances, using Artificial Neural Networks.
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 Côte d’Azur of Nice and the INSU-CNRS in Paris, the Max Planck Institut für Astronomie of
Heidelberg; the University of Leiden and the NOVA-ASTRON Institute of Dwingeloo, the Max Planck Institut für
Radioastronomie of Bonn, the Institut für Theoretische Physik und Astrophysik of Kiel, the Vienna University and the
Konkoly Observatory.
KEYWORDS: Telescopes, Interferometers, Astatine, Interferometry, Large telescopes, Observatories, Systems engineering, Control systems, Mirrors, Sensors
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and
the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in
northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the
operation, the instruments developments are pursued, and new modes are studied and commissioned to offer
a wider range of scientific possibilities to the community and increase sensitivity. New configurations of the
ATs have been offered and are frequently discussed with the science users of the VLTI and implemented to
optimize the scientific return. The PRIMA instrument, bringing astrometry capability to the VLTI and phase
referencing to the instruments is being commissioned. The visitor instrument PIONIER is now fully operational
and bringing imaging capability to the VLTI.
The current status of the VLTI is described with successes and scientific results, and prospects on future
evolution are presented.
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four
1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two
VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the operation, the instruments
developments are pursued, and new modes are studied and commissioned to offer a wider range of scientific possibilities
to the community. New configurations of the ATs array are discussed with the science users of the VLTI and
implemented to optimize the scientific return. The monitoring and improvement of the different systems of the VLTI is a
continuous work. The PRIMA instrument, bringing astrometry capability to the VLTI and phase referencing to the
instruments has been successfully installed and the commissioning is ongoing. The possibility for visiting instruments
has been opened to the VLTI facility.
A working group on interferometry data standards has been established within IAU Commission 54 (Optical/
Infrared Interferometry). The working group includes members representing the major optical interferometry
projects worldwide, and aims to enhance existing standards and develop new ones to satisfy the broad interests
of the optical interferometry community. We present the initial work of the group to enhance the OIFITS data
exchange standard, and outline the software packages and libraries now available which implement the standard.
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8 m Unit Telescopes (UT) and the four
1.8 m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The fourth
AT has been delivered to operation in December 2006, increasing the flexibility and simultaneous baselines access of the
VLTI. Regular science operations are now carried on with the two VLTI instruments, AMBER and MIDI. The FINITO
fringe tracker is now used for both visitor and service observations with ATs and will be offered on UTs in October
2008, bringing thus the fringe tracking facility to VLTI instruments. In parallel to science observations, technical periods
are also dedicated to the characterization of the VLTI environment, upgrades of the existing systems, and development
of new facilities. We will describe the current status of the VLTI and prospects on future evolution.
Since the beginning of the Paranal Service Mode observations, the DFO group is dedicated in monitoring the
VLT/VLTI instruments, in controlling the quality of the data and in providing the principal investigators (PI) with
reduced calibrated data whenever possible. Each year, new instruments are coming into operations, bringing more
complex challenges for our Data Flow Operations.
We will briefly present the VLTI data flow operations implemented for the first VLTI instrument VINCI, then we will
focus on the monitoring of the instruments MIDI and AMBER. For each of these instruments, basics parameters such as
the detector, the instrument alignment are monitored. Calibrations are also processed either for to monitor the stability of
the instrument or/and to be applied to the science data. We also developed more complex procedures to follow the
behavior of the subsystems such as MACAO (adaptive optics), IRIS (fast guiding), FINITO (fringe tracker). Some
procedures have been developed to monitor the instrumental Transfer Function for the different instrument setups and
configurations will be shown. To understand the Transfer Function, it is important to have a good knowledge of the
objects (calibrators) used for the measurement. We will discuss the issue of interferometric calibrators and present the
work on this subject done specifically for VLTI.
In 2008, PRIMA facility will start operations. Its astrometry mode will be commissioned. Like each new VLT/VLTI
instrument this PRIMA astrometric mode will be supported by our group.
The VLTI Data Flow Operations consist in monitoring the performance of the different VLTI instruments offered to the community, in verifying the quality of the calibration and scientific data and their associated products. Since the beginning of MIDI (April 2004) and AMBER (October 2005) Service Mode Operations, scientific as well as calibration data have been accumulated to monitor the instruments and the quality of the observations on different time scales and under different conditions or system configurations. In this presentation, we will describe the Quality Control procedures and give some statistics and results on the different parameters used for instrument monitoring for time scales from hours to years in the case of MIDI. We will show that this includes parameters extracted directly from the instruments (Instrumental Transfer Function, Flux stability, Image Quality, Detector stability...) and parameters extracted from some of the sub-systems associated to the instruments (Adaptive Optics, telescopes used...). We will discuss the development of the monitoring of the instruments once more instrument modes or sub-systems such as PRIMA are offered to the community.
Since April of 2004, the MIDI mid-infrared beam combiner has been used on the VLTI of the European Southern Observatory on Cerro Paranal for service and visitor mode observations. All calibrator data taken are in the public archive, and tools are being developed and used by Paranal Science Operations and Garching Data Flow Operations and Quality Control to study instrument performance and provide users with nightly performance parameters. These tools are also available to the visitors of Paranal. We report on strategies and results for the first interferometric instrument which had been offered to the astronomical community in service mode. That operation model, with users not necessarily experts in interferometry, deserves special attention to the issues of successful use and reliability of the data.
The VLTI has been operating for about 5 years using the VINCI instrument first, and later MIDI. In October 2005
(Period 76) the first Science Operations with the AMBER instrument started, with 14 Open Time proposals in
the observing queues submitted by the astronomical community. AMBER, the near-infrared/red focal instrument
of the VLTI, operates in the bands J, H, and, K (i.e. 1.0 to 2.5 micrometers) with three beams, thus enabling the
use of closure phase techniques. Light was fed from the 8m Unit Telescopes (UT). The Instrument was offered
with the Low Resolution Mode (JHK) and the Medium Resolution Mode in K-band on the UTs. We will present
how the AMBER VLTI Science Operations currently are performed and integrated into the general Paranal
Science Operations, using the extensive experience of Service Mode operations performed by the Paranal Science
operations and in particular applying the know-how learned from the two years of MIDI Science Operations. We
will also be presenting the operational statistics from these first ever Open Time observations with AMBER.
The ESO VLT Interferometer (VLTI) is a general-user facility and is operated in service mode (SM) for a large part of the available time. An important aspect of this SM observing mode is the definition of a set of critical observing conditions that must be met at the time of executing the requested observation. There are a number of observing constraints that are specific to interferometric observations, such as the choice of the array configuration and the hour angle at time of observation, which is processed during the scheduling. On the other hand, classical constraints such as the regular seeing or the lunar illumination are less critical for observations using VLTI instruments than for those using classical VLT instruments. In particular, the use of the adaptive optics system MACAO for VLTI observations employing the Unit Telescopes (UTs) ensures a very good image quality even for moderate environmental conditions. However, the exact dependence between environmental conditions, the performance of the MACAO systems, the wavefront quality at the interferometric instruments, and the accuracy of the final visibility, are not yet known in much detail. In order to investigate this dependence we have started to monitor routinely the environmental conditions, the quality of the MACAO systems, the quality of the acquisition images, and the final data product for all VLTI observations since June 2005. Here, we present the details of this study, as well as first statistics and results.
The ESO Very Large Telescope Interferometer (VLTI) is the first general-user interferometer that offers near- and mid-infrared long-baseline interferometric observations in service and visitor mode to the whole astronomical community. Over the last two years, the VLTI has moved into its regular science operation mode with the two science instruments, MIDI and AMBER, both on all four 8m Unit Telescopes and the first three 1.8m Auxiliary Telescopes. We are currently devoting up to half of the available time for science, the rest is used for characterization and improvement of the existing system, plus additional installations. Since the first fringes with the VLTI on a star were obtained on March 17, 2001, there have been five years of scientific observations, with the different instruments, different telescopes and baselines. These observations have led so far to more than 40 refereed publications. We describe the current status of the VLTI and give an outlook for its near future.
The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reached a major milestone in September 2003 when the mid infrared instrument MIDI was offered for scientific observations to the community. This was only nine months after MIDI had recorded first fringes. In the meantime, the near infrared instrument AMBER saw first fringes in March 2004, and it is planned to offer AMBER in September 2004.
The large number of subsystems that have been installed in the last two years - amongst them adaptive optics for the 8-m Unit Telescopes (UT), the first 1.8-m Auxiliary Telescope (AT), the fringe tracker FINITO and three more Delay Lines for a total of six, only to name the major ones - will be described in this article. We will also discuss the next steps of the VLTI mainly concerned with the dual feed system PRIMA and we will give an outlook to possible future extensions.
We present direct detections of the spatial extent of the circumbinary disk around HR 4049 and its companion. Observations were obtained with the ESO Very Large Telescope Interferometer using the VLT Interferometric Commissioning Instrument (VINCI) at 2 micron and the Mid Infrared Instrument (MIDI) between 8 and 12 micron. A single uniform disk model fit to the VINCI data gives an angular diameter of 27 milli-arcseconds. After taking into account the contribution from an unresolved central star we find that the observed visibilities indicate a second component with a spatial extent of 37 milli-arcseconds (which is identified as the circumbinary disk). The MIDI interferometric spectra show features which are due to PAH emission lines (8.6 and 11.3 micron). The visibilities of the emission lines indicate that the spatial extent in the lines (50 to 60 milli-arcseconds) is larger than in the continuum (35 to 45 milli-arcseconds). This leads us to propose a three emission components model to explain the interferometric observations: a central unresolved star, a 37 milli-arcseconds circumbinary disk and polar lobes emitting in the PAH bands with a size of 50 to 60 milli-arcseconds.
MIDI (MID-infrared Interferometric instrument) gave its first N-band (8 to 13 micron) stellar interference fringes on the VLTI (Very Large Telescope Interferometer) at Cerro Paranal Observatory (Chile) in December 2002. An lot of work had to be done to transform it, from a successful physics experiment, into a premium science instrument which is offered to the worldwide community of astronomers since September 2003. The process of "paranalization", carried out by the European Southern Observatory (ESO) in collaboration with the MIDI consortium, has aimed to make MIDI simpler to use, more reliable, and more efficient. We describe in this paper these different aspects of paranalization (detailing the improvement brought to the observation software) and the lessons we have learnt. Some general rules, for bringing an interferometric instrument into routine operation in an observatory, can be drawn from the experience with MIDI. We also report our experience of the first "service mode" run of an interferometer (VLTI + MIDI) that took place in April 2004.
The ESO Very Large Telescope Interferometer (VLTI) is the first general-user interferometer that offers near- and mid-infrared long-baseline interferometric observations in service mode as well as visitor mode to the whole astronomical community. Regular VLTI observations with the first scientific instrument, the mid-infrared instrument MIDI, have started in ESO observing period P73, for observations between April and September 2004. The efficient use of the VLTI as a general-user facility implies the need for a well-defined operations scheme. The VLTI follows the established general operations scheme of the other VLT instruments. Here, we present from a users' point of view the VLTI specific aspects of this scheme beginning from the preparation of the proposal until the delivery of the data.
The ESO Data Flow Operations group (also called Quality Control group) is dedicated to look into the performance of the different VLT instruments, to verify the quality of the calibration and scientific data, to control and monitor them on different time scales. At ESO headquarters in Garching, Germany, one QC scientist is dedicated to these tasks for the VLTI instruments: VINCI, MIDI, AMBER, and (eventually) PRIMA.
In this paper, we focus on MIDI. In this presentation, we define the tasks of the Quality Control scientist and describe the lessons learned on quality control and instrument trending with the commissioning instrument VINCI. We then illustrate the different aspects of the MIDI Data Flow Operations supported by the QC scientist such as data management issues (data volume, distribution to the community), processing of the data, and data quality control.
Science interferometry instruments are now available at the Very Large Telescope for observations in service mode; the MID-Infrared interferometry instrument, MIDI, started commissioning and has been opened to observations in 2003 and the AMBER 3-beam instrument shall follow in 2004. The Data Flow System is the VLT end-to-end software system for handling astronomical observations from the initial observation proposal phase through to the acquisition, archiving, processing, and control of the astronomical data. In this paper we present the interferometry specific components of the Data Flow System and the software tools which are used for the VLTI.
The VLTI Calibrators Program is a common project between ESO and NEVEC. The main goal is to establish a network of measurements of calibrator objects with an accuracy high enough to fully exploit the different VLTI instruments. We started this project in 2001 by defining a list of objects to be used during the observations with the commissioning instrument VINCI. During the first year of observation (18th March 2001 - 18th March 2002), a total of 5060 observations have been recorded on 156 astronomical objects. More than 60% of the observations have been done on 63 calibrator objects. These calibrator data are currently analyzed to refine the measurements of the adopted diameters. After a brief description of the instrument and of the data reduction process, we describe the criteria used to establish a list of calibrators suitable for the commissioning instrument VINCI with baselines of up to 200m. We define a strategy to observe and analyze the data for the commissioning of the VLTI and of several baselines. We emphasize the difficulties of instrumental calibration to an accuracy of a few 0.1% and the necessity of a long term effort.
The first science instrument for the Very Large Telescope Interferometer (VLTI), the Mid-infrared instrument MIDI, will be commissioned in November 2002 with anticipated first fringe during that commissioning run on the 40-cm Siderostats and the 8.2-meter Unit Telescopes. In this paper we describe scientific and technical observing modes (also referred to as observation procedures) developed for MIDI and discuss in detail how an observing run with the instrument is planned.
MIDI is built by a consortium lead by the Max Planck Institute for Astronomy (MPIA Heidelberg), with contributions from among others ASTRON (Dwingeloo, The Netherlands), Leiden Observatory, University of Amsterdam, Paris Observatory, University of Groningen, the Kiepenheuer-Institut fur Sonnenpysik at Freiburg, Thuringer Landessternwarte Tautenburg, and the Observatoire de la Cote d'Azur.
The start of NEVEC was initiated by the opportunity in the Netherlands to reinstate instrumental efforts in astronomy through a funding program for 'Top Research Schools,’ which brought about the creation of NOVA. The fact that considerable experience exists in Radio Astronomical imaging through interferometry (the Westerbork Synthesis Radio Telescope started in 1970), and the relatively small size at the time of ESO's VLTI Team made it opportune to aim for a win-win situation through collaboration. So presently an MOU between ESO and NOVA is in force, which stipulates that 10 out of the 18 man-years funded by NOVA for NEVEC until 2005 [new personnel, in university setting (Leiden) but on project money] shall be used on tasks that are mutually agreed between NOVA and ESO.
The tasks presently are found in the domain of observing modes, calibration and modeling, as well as contributing to the commissioning of new instruments and thinking about future instruments. Another task, outside these 10 FTE, has been the data handling and analysis software for MIDI, and again contributing to its commissioning. Delivery of the first operational version in Heidelberg has just taken place (summer 2002) contributing to the successful Preliminary Acceptance in Europe for MIDI on September 10, 2002. The actual state of 'products and deliveries' and the future outlook are reviewed.
On March 17, 2001, the VLT interferometer saw for the first time interferometric fringes on sky with its two test siderostats on a 16m baseline. Seven months later, on October 29, 2001, fringes were found with two of the four 8.2m Unit Telescopes (UTs), named Antu and Melipal, spanning a baseline of 102m. First shared risk science operations with VLTI will start in October 2002. The time between these milestones is used for further integration as well as for commissioning of the interferometer with the goal to understand all its characteristics and to optimize performance and observing procedures. In this article we will describe the various commissioning tasks carried out and present some results of our work.
The Data Flow System is the VLT end-to-end system for handling astronomical observations from the initial observation proposal phase through the acquisition, processing and control of the astronomical data. The VLT Data Flow System has been in place since the opening of the first VLT Unit Telescope in 1998. When completed the VLT Interferometer will make it possible to coherently combine up to three beams coming from the four VLT 8.2m telescopes as well as from a set of initially three 1.8m Auxiliary Telescopes, using a Delay Line tunnel and four interferometry instruments. The Data Flow system is now in the process of installation and adaptation for the VLT Interferometer. Observation preparation for a multi-telescope system, handling large data volume of several tens of gigabytes per night are among the new challenges offered by this system. This introduction paper presents the VLTI Data Flow system installed during the initial phase of VLTI commissioning. Observation preparation, data archival, and data pipeline processing are addressed.
Real-time holography compensates for severe aberrations in membrane-mirror based telescope systems. Laboratory demonstrations in both imaging and beam projection have been conducted. Prototype optically addressed liquid-crystal spatial light modulator devices, developed and adapted for this application, are demonstrated with significantly improved diffraction efficiencies.
Gone are the days of unfettered government spending. An affordable, high performance alternative to multi-million dollar adaptive optics systems is required by the scientific and industrial communities. We have constructed and now give early performance specifications for the 1 St ofthree low cost Adaptive Optics systems for the University of Puerto Rico Imaging Interferometer. Built in months, not years, our in-house subsystem developments include (1) a photon counting ICCD Shack-Hartmann wavefront sensor; (2) a zero latency analog wavefront reconstructor; (3) a precision 2D geometry interpolator; (4) a 700Hz bandwidth beamsteering mirror system with photon counting tracker; and (5)adata acquisition, monitoring and deformable mirror control computer. Key to the control system is a 37-element MEM electrostatic membrane deformable mirror purchased from OKO Technologies. Every element of this system is innovative in the sense of exceptionally high performance at low cost. We will discuss the applicability of using several unique 2D liquid crystal spatial light modulators as correcting elements. We will discuss feedback vs. feed-forward implementations of control law, as well as many practical considerations of full implementation. Other possible medical, industrial, and scientific applications of this affordable, high performance AO technology will be presented.
KEYWORDS: Wavefront sensors, Analog electronics, CCD cameras, Cameras, Wavefronts, Signal to noise ratio, Sensors, Quantum efficiency, Data acquisition, Charge-coupled devices
The contradiction inherent in high temporal bandwidth adaptive optics wavefront sensing at low-light-levels (LLL) has driven many researchers to consider the use of high bandwidth high quantum efficiency (QE) CCD cameras with the lowest possible readout noise levels. Unfortunately, the performance of these relatively expensive and low production volume devices in the photon counting regime is inevitably limited by readout noise, no matter how arbitrarily close to zero that specification may be reduced. Our alternative approach is to optically couple a new and relatively inexpensive Ultra Blue Gen III image intensifier to an also relatively inexpensive high bandwidth CCD camera with only moderate QE and high rad noise. The result is a high bandwidth broad spectral response image intensifier with a gain of 55,000 at 560 nm. Use of an appropriately selected lenslet array together with coupling optics generates 16 X 16 Shack-Hartmann type subapertures on the image intensifier photocathode, which is imaged onto the fast CCD camera. An integral A/D converter in the camera sends the image data pixel by pixel to a computer data acquisition system for analysis, storage and display. Timing signals are used to decode which pixel is being rad out and the wavefront is calculated in an analog fashion using a least square fit to both x and y tilt data for all wavefront sensor subapertures. Finally, we present system level performance comparisons of these new concept wavefront sensors versus the more standard low noise CCD camera based designs in the low-light-level limit.
A two multi-ro telescope interferometer was built at Air Force Research Lab in Albuquerque New Mexico as a development testbed. The principal objective of this testbed is to develop existing techniques and to test novel low-cost technologies for applications in future interferometers. These technologies include a tip/tilt piston mirror that has a 500-Hz bandwidth with a 200-wave adjustable piston capability at 633nm. This type of mirror has been installed on both telescopes and is used to track objects and scan for fringes. The data obtained on these objects will be used to determine algorithms for measuring fringe visibility at low light level. Additional technologies include liquid crystal devices that have been used to correct static aberrations in the optical system and will be used with a new wavefront sensing technique to correct low order atmospheric aberrations. The new wavefront sensor currently being developed in-house uses a GEN III intensifier optically coupled to a Dalsa camera to provide atmospheric correction on faint extended objects. The testbed will also be utilized to test single mode fiber optics as a replacement to traditional recombining optics. This will potentially reduce the cost and simplify the alignment of multi telescope interferometers.
The University ofPuerto Rico, Mayaguez, in conjunction with the Deep Space Surveillance Branch (DEBS) ofthe USAF Research Laboratory (AFRL) Phillips Site (PL) in Albuquerque, NM is initiating an Adaptive Optics (AO) Interferometry program. The program will begin with four projects. We currently have finding for a three element optical interferometer, described in this paper, using Technology developed at DEBS, for a new wavefront sensor and a Liquid Crystal (LC) wavefront compensator being presented at this meeting'9.and a Low Light Level Fringe Tracker (LLLFT)"6'1"24 Michelson: Interferometer. We are also developing a program to put a similarly configured inexpensive two-element interferometer test-bed in orbit. The interferometer would have optical elements on a 10-meter boom. It will use Aperture Synthesis by rotation and motion ofthe elements along the booms. The third project under development would incorporate the initial 3-element interferometer into a larger array with the additional collaboration ofNew Mexico Tech and New Mexico State University at a 10,600' site near Socorro, NM. As part ofthe ground based interferometry effort we are trying to develop inexpensive meter class telescopes. The 0.75meter telescopes we are building for our small interferometer will serve as prototypes and system test-beds. The telescopes will be robotic, remotely operable, essentially self-orienting, and portable. We hope to produce such systems for commercial distribution for approximately $250K each. All ofthe ground-based interferometric systems will be configured for remote operation and independent use ofsub-arrays while upgrades and repairs are underway. The major thrust ofthe UPR effort will be to develop inexpensive interferometers for diverse applications with the low light level capabilities and the LC adaptive optics developed at the Phillips Site. Particular applications will be for high-resolution astronomy and satellite imaging. The adaptive optics will be such that they can be placed on the individual telescopes and are not part ofthe interferometer. They will then serve as templates fbr AO systems ofgeneral interest. As an additional part ofall ofthese projects we will try to develop the use ofoptical fibers for several applications. We would like to couple the telescopes with fiber if we can develop an efficient way to couple the output signal from the telescope to the fibers. in addition we hope to use fiber stretchers for optical path compensation to replace expensive conventional optical delay lines. Key words; adaptive optics, interferometer, Liquid Crystal wavefront compensation
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