The Prefocal Station (PFS) is the last opto-mechanical unit before the telescope focal plane in the Extremely Large Telescope (ELT) optical train. The PFS distributes the telescope optical beam to the Nasmyth and Coudé instrument focal stations and it contains all of the sky metrology (imaging and wavefront sensing) that will be used by the active optics of the telescope and to support operations such as phasing the primary mirror (phasing and diagnostic station). It also hosts local metrology that will be used for coarse alignment and maintenance. We present the main results of a concept design study for the Nasmyth A prefocal station.
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.
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.
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 Nasmyth platforms of the E-ELT will contain one Prefocal Station (PFS) each. The main PFS functional requirements are to provide a focal plane to the three Nasmyth focal stations and the Coudé focus, optical sensing supporting telescope low order optimisation and seeing limited image quality, and optical sensing supporting characterising and phasing of M1 and other telescope subsystems. The PFS user requirements are used to derive the PFS technical requirements specification that will form the basis for design, development and production of the system. This specification process includes high-level architectural decisions and technical performance budget allocations. The mechanical design concepts reported here have been developed in order to validate key system specifications and associated technical budgets.
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.
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 New Adaptive Optics Module for Interferometry (NAOMI)<sup>1</sup> 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<sup>2</sup> are designed for interferometry which they are essentially dedicated for. Currently the AT’s are equipped with a fast, visible tip-tilt sensor called STRAP<sup>3</sup> (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.
The Adaptive Optics Facility project is completing the integration of its systems at ESO Headquarters in Garching. The main test bench ASSIST and the 2<sup>nd</sup> Generation M2-Unit (hosting the Deformable Secondary Mirror) have been granted acceptance late 2012. The DSM has undergone a series of tests on ASSIST in 2013 which have validated its optical performance and launched the System Test Phase of the AOF. This has been followed by the performance evaluation of the GRAAL natural guide star mode on-axis and will continue in 2014 with its Ground Layer AO mode. The GALACSI module (for MUSE) Wide-Field-Mode (GLAO) and the more challenging Narrow-Field-Mode (LTAO) will then be tested. The AOF has also taken delivery of the second scientific thin shell mirror and the first 22 Watt Sodium laser Unit. We will report on the system tests status, the performances evaluated on the ASSIST bench and advancement of the 4Laser Guide Star Facility. We will also present the near future plans for commissioning on the telescope and some considerations on tools to ensure an efficient operation of the Facility in Paranal.
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.
The Enhanced Resolution Imager and Spectrograph (ERIS) is the next-generation instrument planned for the Very Large
Telescope (VLT) and the Adaptive Optics Facility (AOF)<sup>1</sup>. It is an AO assisted instrument that will make use of the
Deformable Secondary Mirror and the new Laser Guide Star Facility (4LGSF), and it is designed for the Cassegrain
focus of the telescope UT4. The project just concluded its conceptual design phase and is awaiting formal approval to
continue to the next phase. ERIS will offer 1-5 μm imaging and 1-2.5 μm integral field spectroscopic capabilities with
high Strehl performance. As such it will replace, with much improved single conjugated AO correction, the most
scientifically important and popular observing capabilities currently offered by NACO<sup>2</sup> (diffraction limited imaging in JM
band, Sparse Aperture Masking and APP coronagraphy) and by SINFONI<sup>3</sup>, whose instrumental module, SPIFFI, will
be re-used in ERIS. The Cassegrain location and the performance requirements impose challenging demands on the
project, from opto-mechanical design to cryogenics to the operational concept. In this paper we describe the baseline
design proposed for ERIS and discuss these technical challenges, with particular emphasis on the trade-offs and the
novel solutions proposed for building ERIS.
The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser
driven adaptive telescope with a deformable mirror in its optical train.
The project has completed the procurement phase and several large structures have been delivered to Garching
(Germany) and are being integrated (the AO modules GRAAL and GALACSI and the ASSIST test bench). The 4LGSF
Laser (TOPTICA) has undergone final design review and a pre-production unit has been built and successfully tested.
The Deformable Secondary Mirror is fully integrated and system tests have started with the first science grade thin shell
mirror delivered by SAGEM. The integrated modules will be tested in stand-alone mode in 2012 and upon delivery of
the DSM in late 2012, the system test phase will start. A commissioning strategy has been developed and will be updated
before delivery to Paranal. A substantial effort has been spent in 2011-2012 to prepare the unit telescope to receive the
AOF by preparing the mechanical interfaces and upgrading the cooling and electrical network. This preparation will also
simplify the final installation of the facility on the telescope.
A lot of attention is given to the system calibration, how to record and correct any misalignment and control the whole
facility. A plan is being developed to efficiently operate the AOF after commissioning. This includes monitoring a
relevant set of atmospheric parameters for scheduling and a Laser Traffic control system to assist the operator during the
night and help/support the observing block preparation.
GALACSI is one of the Adaptive Optics (AO) systems part of the ESO Adaptive Optics Facility (AOF). It will use the
VLT 4-Laser Guide Stars system, high speed and low noise WaveFront Sensor cameras (<1e-, 1000Hz) the
Deformable Secondary Mirror (DSM) and the SPARTA Real Time Computer to sharpen images and enhance faint
object detectability of the MUSE Instrument. MUSE is an Integral Field Spectrograph working at wavelengths from
465nm to 930nm. GALACSI implements 2 different AO modes; in Wide Field Mode (WFM) it will perform Ground
Layer AO correction and enhance the collected energy in a 0.2" by 0.2" pixel by a factor 2 at 750nm over a Field of
View (FoV) of 1' by 1'. The 4 LGSs and one tip tilt reference star (R-mag <17.5) are located outside the MUSE FoV.
Key requirements are to provide this performance and a very good image stability for a 1hour long integration time. In
Narrow Field Mode (NFM) Laser Tomography AO will be used to reconstruct and correct the turbulence for the center
field using the 4 LGSs at 15" off axis and the Near Infra Red (NIR) light of one reference star on axis for tip tilt and
focus sensing. In NFM GALACSI will provide a moderate Strehl Ratio of 5% (goal 10%) at 650nm. The NFM hosts
several challenges and many subsystems will be pushed to their limits. The opto mechanical design and error budgets
of GALACSI is described here.
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
The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser
driven adaptive telescope with a deformable mirror in its optical train, in this case the secondary 1.1m mirror, and four
Laser Guide Stars (LGSs). This evolution implements many challenging technologies like the Deformable Secondary
Mirror (DSM) including a thin shell mirror (1.1 m diameter and 2mm thin), the high power Na lasers (20W), the low
Read-Out Noise (RON) WaveFront Sensor (WFS) camera (< 1e-) and SPARTA the new generation of Real Time
Computers (RTC) for adaptive control. It also faces many problematic similar to any Extremely Large Telescope (ELT)
and as such, will validate many technologies and solutions needed for the European ELT (E-ELT) 42m telescope. The
AOF will offer a very large (7 arcmin) Field Of View (FOV) GLAO correction in J, H and K bands (GRAAL+Hawk-I),
a visible integral field spectrograph with a 1 arcmin GLAO corrected FOV (GALACSI-MUSE WFM) and finally a
LTAO 7.5" FOV (GALACSI-MUSE NFM). Most systems of the AOF have completed final design and are in
manufacturing phase. Specific activities are linked to the modification of the 8m telescope in order to accommodate the
new DSM and the 4 LGS Units assembled on its Center-Piece. A one year test period in Europe is planned to test and
validate all modes and their performance followed by a commissioning phase in Paranal scheduled for 2014.
CRIRES is a cryogenic, pre-dispersed, infrared Echelle spectrograph designed to provide a nominal resolving
power ν/Δν of 10<sup>5</sup> between 1000 and 5000 nm for a nominal slit width of 0.2". The CRIRES installation at
the Nasmyth focus A of the 8-m VLT UT1 (Antu) marks the completion of the original instrumentation plan
for the VLT. A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide 0.2"
spatial resolution along the slit. A mosaic of four Aladdin InSb-arrays packaged on custom-fabricated ceramic
boards has been developed. It provides for an effective 4096 × 512 pixel focal plane array to maximize the free
spectral range covered in each exposure. Insertion of gas cells is possible in order to measure radial velocities with
high precision. Measurement of circular and linear polarization in Zeeman sensitive lines for magnetic Doppler
imaging is foreseen but not yet fully implemented. A cryogenic Wollaston prism on a kinematic mount is already
incorporated. The retarder devices will be located close to the Unit Telescope focal plane. Here we briefly recall
the major design features of CRIRES and describe the commissioning of the instrument including a report of
extensive testing and a preview of astronomical results.
GLAS (Ground-layer Laser Adaptive optics System) provides a Rayleigh Laser Guide Star (LGS) upgrade to the existing
NAOMI AO system at the 4.2-m William Herschel Telescope on La Palma. Installation of the GLAS upgrades
commenced in 2006 with on-sky commissioning taking place from May 2007. Commissioning was very successful and
AO correction was first observed during the August 2007 observing run. Here we present an overview of the opto-mechanical
systems that have been installed and commissioned, including the LGS launch system, LGS safety systems
and LGS Wave Front Sensor, concentrating on the integration of the various optical and optoelectronic components.
The Nasmyth Adaptive Optics for Multi-purpose Instrumentation (NAOMI) on the William Herschel Telescope (WHT) has been developed recently into a common user AO (Adaptive Optics) instrument to accompany OASIS (Optically Adaptive System for Imaging Spectroscopy), a multi-slit spectrograph and INGRID (Isaac Newton Group Red Imaging Device) an Infrared detector. The most recent changes are the addition of an Atmospheric Dispersion Corrector (ADC) to be used for the optical wavelengths and a Dichroic Changer mechanism to select either a pass band or IR light for the Universal Science Ports (UPS).
Future developments on NOAMI are planned as it is due to house the GLAS WFS (Ground Layer Adaptive optics System Wave Front Sensor), a wave front sensor for the future Laser Guide Star (LGS) system to be installed on the WHT in 2006.
This paper describes the changes made with respect to the science ports and the changes to be made for the GLAS WFS; focusing on the GLAS WFS and the optical path and interface to the NAOMI adaptive optics system.
The GLAS (Ground-layer Laser Adaptive-optics System) project is to construct a common-user Rayleigh laser beacon that will work in conjunction with the existing NAOMI adaptive optics system, instruments (near IR imager INGRID, optical integral field spectrograph OASIS, coronagraph OSCA) and infrastructure at the 4.2-m William Herschel Telescope (WHT) on La Palma. The laser guide star system will increase sky coverage available to high-order adaptive optics from ~1% to approaching 100% and will be optimized for scientific exploitation of the OASIS integral-field spectrograph at optical wavelengths. Additionally GLAS will be used in on-sky experiments for the application of laser beacons to ELTs. This paper describes the full range of engineering of the project ranging through the laser launch system, wavefront sensors, computer control, mechanisms, diagnostics, CCD detectors and the safety system. GLAS is a fully funded project, with final design completed and all equipment ordered, including the laser. Integration has started on the WHT and first light is expected summer 2006.
The 4.2m William Herschel Telescope (WHT) at the Isaac Newton Group of Telescopes (ING) is due to have a new
Rayleigh laser beacon installed. This will form part of the Ground-layer Laser Adaptive optic System (GLAS). GLAS
will compliment the existing Nasmyth Adaptive Optic Multipurpose Instrument (NAOMI) currently in operation and
allow for much greater sky coverage than before.
A 30W laser will be launched from behind the secondary mirror of the WHT. To facilitate this, a support has been
designed to mount the laser on the top end ring of the telescope. The mount is designed to give a gravity stable platform
in a thermally stable environment. The mount required the use of astatic levers to help maintain alignment with the
telescope. The laser beam is steered over the telescope vanes and into the Beam Launch Telescope (BLT) which is
mounted behind the secondary mirror. The BLT then expands the beam and launches it to 20Km. Two wavefront sensors
are used to correct the image. The laser guide star wavefront sensor (LGS WFS) uses a beamsplitter to pickoff the laser
return at its wavelength. The existing NAOMI WFS is still used but is now the natural guide star wavefront sensor (NGS
WFS) and corrects for tip/tilt.
This paper will concentrate on describing the mechanical design and FEA of the laser up launch system (laser cradle and
mount and the BLT). A very brief overview of the LGS WFS will be given for system completeness.
The William Herschel Telescope (WHT) has an adaptive optics (AO) suite consisting of the AO system NAOMI, near IR imager INGRID, optical field spectrograph OASIS and coronagraph OSCA. GRACE (<b>GR</b>ound based <b>A</b>daptive optics <b>C</b>ontrolled <b>E</b>nvironment) is a dedicated structure at a Nasmyth focus designed to facilitate routine AO use by providing a controlled environment for the instrument system. However, GRACE is not just a building; it is all of the systems associated with providing the controlled environment, especially the control of air quality, temperature and flow. A key concern was that adding the GRACE building to the Nasmyth platform would not adversely change the telescope performance. This paper gives the background to GRACE, its specification and design, the building construction and installation, the environmental controls installed and their performance, the services provided, the effect of the new structure on telescope performance, the results of the project, including the effect having a controlled environment on AO performance and its planned use for a Rayleigh laser guide star system.
The Nasmyth Adaptive Optics Multipurpose Instrument (NAOMI) is the adaptive optics (AO) platform on the 4.2m William Herschel Telescope (WHT) at the Isaac Newton Group of Telescopes (ING). Until recently NAOMI has been concentrating on near infrared observations using the Isaac Newton Group Red Imaging Device (INGRID). Recent developments have added an extra optical port to NAOMI. The observer can now rapidly switch between infrared and optical instrumentation during AO observing, making the system more appealing for visiting instruments.
To allow for the operation of the common user optical spectrograph OASIS, a new optical path was created around the existing NAOMI optics. Various mechanisms were also added to the whole optical system. The OASIS beam was reshaped to f/20. The original optical/IR beam remains unchanged at f/16, and forms a new universal science port (USP). The existing Nasmyth Calibration Unit (NCU) has been replaced with a new design. This new NCU has multiple fibre-fed light sources that include continuum and arc lamps. The intensity of light can be individually adjusted via computer control. A new acquisition camera is mounted such that it can be used simultaneously with the spectral lamps. Software upgrades now allow faster deformable mirror calibration. A moveable mirror is used to select which science port will receive the light. Enhancements to the NAOMI AO system are discussed in this paper and suggestions for possible future upgrades.
NAOMI is the AO system of the 4.2-m William Herschel Telescope on La Palma. It delivers near-diffraction-limited images in the IR, and a significantly improved PSF at optical wavelengths. The science cameras currently comprise an IR imager (INGRID), an optical integral-field spectrograph (OASIS) and a coronagraph which may be placed in the light path to either instrument. 19 science programmes were observed during 2002-3. Observing overheads are small, with as much as 60% of the night spent integrating on science targets. In late 2004 this year, the WFS will be equipped with a low-noise L3 CCD, giving a gain of a factor of 2 in S:N for faint guide stars. A Rayleigh laser guide star is under development, with first light expected summer 2006, providing a unique facility: AO-corrected optical integral-field spectroscopy anywhere on the northern sky.
This paper describes an engineering programme to retrofit an improved mechanism control system to the Isaac Newton Group Red Imaging Device (INGRID), the infrared camera at the William Herschel Telescope. INGRID is an operational instrument and engineering upgrades need to be considered carefully with a view to minimising risks to the instrument and ensuring that it is back in service on the due date.
A number of alternative mechanical arrangements were considered; different stepper motor candidates were assessed together with the electronics to drive them. Motor drive parameters were optimised to increase the speed of optical setup. Finally, different technologies were considered for improving the arrangements for sensing the position of the instrument's mechanism wheels. The paper reports on the results of this programme and lessons learned.
In July 2001, AutoFib-2 (AF2), the prime focus robotic fiber positioner for the Isaac Newton Group's (ING) 4.2m William Hershel Telescope (WHT) had its new Small Fiber Module (SFM) successfully commissioned. The new SFM contains 150 science fibers and 10 fiducial bundles.
Each science fiber has a diameter of 90 μm, which corresponds to 1.6 arcsec in the sky. The continuous science fibers are fed into the Nasmyth platform Wide Field Fiber Optic Spectrograph (WYFFOS). Each fiducial bundle, 450 μm in diameter, contains 10,000 coherent fibers providing a rough imaging capability over an 8 arcsec round field.
This paper looks at the reasons for developing this module, examines its mechanical design, describes its new science and fiducial fibers, looks at the fiber alignment techniques used, explains the new guiding system and briefly discusses changes in the AF2 control system. It continues to reveal the results of some fiber characterization experiments performed on sky and gives an example of a recent science run. The paper concludes with a section that lists planned AF2 enhancements.