With the advent of 30- to 40-m class ground-based telescopes in the mid-2020s, direct imaging of exoplanets is bound to take a new major leap. Among the approved projects, the Mid-infrared Extremely Large Telescope (ELT) Imager and Spectrograph (METIS) instrument for the ELT holds a prominent spot; by observing in the mid-infrared regime, it will be perfectly suited to study a variety of exoplanets and protoplanetary disks around nearby stars. Equipped with two of the most advanced coronagraphs, the vortex coronagraph and the apodizing phase plate, METIS will provide high-contrast imaging (HCI) in L-, M- and N-bands, and a combination of high-resolution spectroscopy and HCI in L- and M-bands. We present the expected HCI performance of the METIS instrument, considering realistic adaptive optics residuals, and investigate the effect of the main instrumental errors. The most important sources of degradation are identified and realistic sensitivity limits in terms of planet/star contrast are derived.
METIS is the Mid-infrared Extremely large Telescope Imager and Spectrograph, one of the first generation instruments of ESO’s 39m ELT. All scientific observing modes of METIS require adaptive optics (AO) correction close to the diffraction limit. Demanding constraints are introduced by the foreseen coronagraphy modes, which require highest angular resolution and PSF stability. Further design drivers for METIS and its AO system are imposed by the wavelength regime: observations in the thermal infrared require an elaborate thermal, baffling and masking concept. METIS will be equipped with a Single-Conjugate Adaptive Optics (SCAO) system. An integral part of the instrument is the SCAO module. It will host a pyramid type wavefront sensor, operating in the near-IR and located inside the cryogenic environment of the METIS instrument. The wavefront control loop as well as secondary control tasks will be realized within the AO Control System, as part of the instrument. Its main actuators will be the adaptive quaternary mirror and the field stabilization mirror of the ELT. In this paper we report on the phase B design work for the METIS SCAO system; the opto-mechanical design of the SCAO module as well as the control loop concepts and analyses. Simulations were carried out to address a number of important aspects, such as the impact of the fragmented pupil of the ELT on wavefront reconstruction. The trade-off that led to the decision for a pyramid wavefront sensor will be explained, as well as the additional control tasks such as pupil stabilization and compensation of non-common path aberrations.
Pyramid wavefront sensors (PWFS) have been agreed to provide a superior faint-end performance with respect to Shack-Hartmann systems (SHS) quite some time ago. However, much of the advantage relies on the fact that PWFSs exploit the full resolution limit of the telescope. ELTs will thus confront PWFSs with an unprecedented number of resolved targets. To analyze the behavior of PWFS on extended targets in detail observationally is difficult. We will present the result of simulations representing the Single-Conjugated Adaptive Optics (SCAO) system of METIS on the European ELT (E-ELT).
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 Coudé room, thus aptly named Coudé Infrared Adaptive Optics (CIAO). This paper describes the CIAO design, assembly, integration and verification at the Paranal observatory.
The direct detection of low-mass planets in the habitable zone of nearby stars is an important science case for future E-ELT instruments such as the mid-infrared imager and spectrograph METIS, which features vortex phase masks and apodizing phase plates (APP) in its baseline design. In this work, we present end-to-end performance simulations, using Fourier propagation, of several METIS coronagraphic modes, including focal-plane vortex phase masks and pupil-plane apodizing phase plates, for the centrally obscured, segmented E-ELT pupil. The atmosphere and the AO contributions are taken into account. Hybrid coronagraphs combining the advantages of vortex phase masks and APPs are considered to improve the METIS coronagraphic performance.
METIS, the Mid-nfrared E-ELT Imager and Spectrometer, will be providing high-sensitivity imaging and high-resolution spectroscopy in the mid-infrared (3-19 micrometer) to the E-ELT. In order to achieve the exceptional performance required by its driving science cases, exoplanets and proto-planetary disks, METIS will be featuring two Adaptive Optics (AO) systems — a first-light Single Conjugate Adaptive Optics (SCAO) system, complemented by a Laser Tomographic Adaptive Optics (LTAO) system, most likely, a few years after first light. METIS, being one of the three first light science instruments on the European Extremely Large Telescope (E-ELT), will be one of the first instruments using the integrated deformable mirror of the E-ELT for its Adaptive Optics (AO) correction.
The internal SCAO system designed to maximize the performance for bright targets and has its wavefront sensors (WFSs) build inside the METIS cryostat to minimize the number of warm surfaces towards the science detectors. Although the internal dichroic will reflect all light short wards of 3 micrometers towards the WFS, only the IR light will most likely be used, mainly due to the expected improved performance at longer wavelengths for the WFS. A trade-off has been made between both visible versus infrared wave front sensing as well as Pyramid versus Shack-Hartmann, under various observing conditions and target geometries, taking into account performance, target availability, reliability and technology readiness level. The base line for the SCAO system is to minimize system complexity, thereby ensuring system availability and reliability even under first-light conditions.
Since the SCAO system will require a bright guide star near the science target, it can only be used for a limited number of targets. The LTAO system, consisting of up to 6 LGS and up to 3 low-order NGS WFS and located outside the cryostat, is designed to increase the sky coverage on arbitrary targets to >80%. Investigations are ongoing if the internal SCAO system can be used as either a Low-Order WFS or metrology system.
GRAVITY, a second generation instrument for the Very Large Telescope Interferometer (VLTI), will provide an astrometric precision of order 10 micro-arcseconds, an imaging resolution of 4 milli-arcseconds, and low/medium resolution spectro-interferometry. These improvements to the VLTI represent a major upgrade to its current infrared interferometric capabilities, allowing detailed study of obscured environments (e.g. the Galactic Center, young dusty planet-forming disks, dense stellar cores, AGN, etc...). Crucial to the final performance of GRAVITY, the Coudé IR Adaptive Optics (CIAO) system will correct for the effects of the atmosphere at each of the VLT Unit Telescopes. CIAO consists of four new infrared Shack-Hartmann wavefront sensors (WFS) and associated real-time computers/software which will provide infrared wavefront sensing from 1.45-2.45 microns, allowing AO corrections even in regions where optically bright reference sources are scarce. We present here the latest progress on the GRAVITY wavefront sensors. We describe the adaptation and testing of a light-weight version of the ESO Standard Platform for Adaptive optics Real Time Applications (SPARTA-Light) software architecture to the needs of GRAVITY. We also describe the latest integration and test milestones for construction of the initial wave front sensor.
Large flat mirrors can be characterized using a standard interferometer coupled with stitching the subaperture
measurement data. Such systems can measure the global full map of the optical surface by minimizing the inconsistency
of data in the adjacent regions. We present a stitching technique that makes use of a commercial phase-shifting Twyman-
Green interferometer in combination with an iterative optimized stitching algorithm. The proposed method has been
applied to determine the surface errors of planar mirrors with an accuracy of a few nanometers. Moreover, the effect of
reference wavefront error is explored. The feasibility and the performance of the proposed system are also demonstrated,
along with a detailed error analysis and experimental results.
The ‘Mid-infrared ELT Imager and Spectrograph’ (METIS) will be the third instrument on the European Extremely
Large Telescope (E-ELT). METIS will provide diffraction limited imaging in the atmospheric L/M and N-band from 3
to 14 μm over an 18˝×18˝ field of view, as well as high contrast coronagraphy, medium-resolution (R ≤ 5000) long slit
spectroscopy, and polarimetry. In addition, an integral field spectrograph will provide a spectral resolution of R ~
100,000 at L/M band. Focusing on highest angular resolution and high spectral resolution, METIS will deliver unique
science, in particular in the areas of exo-planets, proto-planetary-disks and high-redshift galaxies, which are illustrated in
this paper. The reduction of the E-ELT aperture size had little impact on the METIS science case. With the recent
positive developments in the area of detectors, the METIS instrument concept has reached a high level of technology
readiness. For some key components (cryogenic chopping mirror, immersed grating, sorption cooler and cryogenic
derotator) a development and test program has been launched successfully.
GRAVITY is a second generation instrument for the VLT Interferometer, designed to enhance the near-infrared
astrometric and spectro-imaging capabilities of VLTI. Combining beams from four telescopes, GRAVITY will
provide an astrometric precision of order 10 micro-arcseconds, imaging resolution of 4 milli-arcseconds, and low
and medium resolution spectro-interferometry, pushing its performance far beyond current infrared interferometric
capabilities. To maximise the performance of GRAVITY, adaptive optics correction will be implemented
at each of the VLT Unit Telescopes to correct for the e_ects of atmospheric turbulence. To achieve this, the
GRAVITY project includes a development programme for four new wavefront sensors (WFS) and NIR-optimized
real time control system. These devices will enable closed-loop adaptive correction at the four Unit Telescopes
in the range 1.4-2.4 μm. This is crucially important for an e_cient adaptive optics implementation in regions
where optically bright references sources are scarce, such as the Galactic Centre. We present here the design of
the GRAVITY wavefront sensors and give an overview of the expected adaptive optics performance under typical
observing conditions. Bene_ting from newly developed SELEX/ESO SAPHIRA electron avalanche photodiode
(eAPD) detectors providing fast readout with low noise in the near-infrared, the AO systems are expected to
achieve residual wavefront errors of 400 nm at an operating frequency of 500 Hz.≤
METIS, the Mid-infrared E-ELT Imager and Spectrometer is foreseen to be the third instrument on the European
Extremely Large Telescope (E-ELT) and the only instrument to provide high sensitivity mid-IR imaging and
spectroscopy to the E-ELT.
In order to reach the maximum resolution and sensitivity, an adaptive optics system is required. Since the operational
wavelength of METIS is the longest of all E-ELT instruments and the field is relatively small, the complexity of the AO
system is significantly reduced, both in required speed as well as order of the AO system.
Adaptive Optics has been demonstrated to deliver consistently high performance for the current generation of 6-10 meter
class telescopes at mid-infrared wavelengths, and similar performance is expected for METIS on the E-ELT. But in order
to provide a reliable system on the E-ELT, several effects which have a minor impact on 6-8 meter class telescopes will
need to be investigated for their impact on METIS AO. These effects include refractivity, atmospheric composition
variations, but also the operation in a complex operational environment given by both METIS as well as the E-ELT. In
this paper we describe the scientific requirements on the METIS AO system, the specific issues related to Adaptive
Optics in the mid-IR and expected performance of the METIS AO system on the E-ELT.
The GRAVITY instrument’s adaptive optics system consists of a novel cryogenic near-infrared wavefront sensor to be
installed at each of the four unit telescopes of the VLT. Feeding the GRAVITY wavefront sensor with light in the 1.4 -
2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built
optical components are required. Here we report on optical and near-infrared testing of the silicon entrance windows of the wavefront sensor cryostat and other reflective optics used in the warm feeding optics.
When testing the optical surface errors with an interferometer, it is always important to determine the residual errors in
the interferometer optics. The calibration of reference optic for proper accuracy is very important issue if the precise
phase measurement results are to be obtained using interferometer. A simple ball calibration method is discussed and the
sufficient number of measurements for the ball averaging calibration is determined. Further we analysis some errors,
which limit the performance of the calibration method by using a combination of both ray optics and wave optics
We present the adaptive optics simulations we have performed to dimension the Gravity adaptive optics wavefront
sensor. We first computed the optimal WFS bandpass, depending on the sampling frequency, detector readout
noise and reference source colour/temperature. We then performed adaptive optics simulations with the YAO
simulation tool for different WFS parameters (number of subpupils, number of pixels per subpupil, loop frequency,
reference source magnitude, etc). Results demonstrate that the Gravity adaptive optics top-level requirements
can be fulfilled with a 9×9 subaperture Shack-Hartmann with 4 pixels per subaperture using an H+K filter, a
larger filter being recommended for sources bluer than 770 K reference source of the Galactic Centre.
METIS (Mid-infrared E-ELT Imager and Spectrometer) is the
mid-infrared instrument proposed for the European
Extremely Large Telescope (E-ELT). METIS will be the first instrument in the mid-IR that will actually require an
Adaptive Optics system in order to reach a performance close to the diffraction limit. Extending Adaptive Optics for the
mid-IR from the current generation of telescopes to 30-42 meter telescopes is technically challenging, but appears at first
sight significantly easier than at visible and near infrared wavelengths.
Adaptive Optics has been demonstrated to deliver Strehl Ratios exceeding 95% on 6-8 meter class telescopes at 10
microns, but achieving this performance on E-ELTs under normal observation conditions, requires that several higher
order effects are taken into account. The performance of a mid-IR AO system drops significantly if refractivity effects
and atmospheric composition variations are not compensated. Reaching Strehl Ratios of over 90% in the L, M and N
band will require special considerations and will impact the system design and control scheme of AO systems for mid-IR
The METIS instrument has finalized its preliminary design phase and in this paper we present the results of our
performance estimates of the METIS AO system. We have included the effects of refractivity and composition
fluctuations on the performance of the AO system and we have investigated how these effects impact the science cases
for mid-IR instrumentation on an ELT.
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 μas 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.
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to
provide imaging and spectroscopic capabilities in the 3μm to 14μm region up to a spectral resolution of 100.000. Here
the technical concept of METIS is described which has been developed based on an elaborated science case which is
presented elsewhere in this conference.
There are five main opto-mechanical modules all integrated into a common cryostat: The fore-optics is re-imaging the
telescope focal plane into the cryostat, including a chopper, an optical de-rotator and an un-dispersed pupil stop. The
imager module provides diffraction limited direct imaging, low-resolution grism spectroscopy, polarimetry and
coronagraphy. The high resolution IFU spectrograph offers a spectral resolution of 100.000 for L- and M-band and
optional 50.000 for the N-band. In addition to the WFS integrated into the E-ELT, there is a METIS internal on-axis
WFS operating at visual wavelengths. Finally, a cold (and an external warm) calibration unit is providing all kinds of
spatial and spectral calibrations capabilities. METIS is planned to be used at one of the direct Nasmyth foci available at
This recently finished Phase-A study carried out within the framework of the ESO sponsored E-ELT instrumentation
studies has been performed by an international consortium with institutes from Germany, Netherlands, France, United
Kingdom and Belgium.
We present the second-generation VLTI instrument GRAVITY, which currently is in the preliminary design phase.
GRAVITY is specifically designed 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 have identified the key design features needed to achieve this
goal and present the resulting instrument concept. It includes an integrated optics, 4-telescope, dual feed beam combiner
operated in a cryogenic vessel; near infrared wavefront sensing adaptive optics; fringe tracking on secondary sources
within the field of view of the VLTI and a novel metrology concept. Simulations show that the planned design matches
the scientific needs; in particular that 10µas astrometry is feasible for a source with a magnitude of K=15 like Sgr A*,
given the availability of suitable phase reference sources.
The very large telescope (VLT) interferometer (VLTI) in its current operating state is equipped with high-order
adaptive optics (MACAO) working in the visible spectrum. A low-order near-infrared wavefront sensor (IRIS)
is available to measure non-common path tilt aberrations downstream the high-order deformable mirror. For
the next generation of VLTI instrumentation, in particular for the designated GRAVITY instrument, we have
examined various designs of a four channel high-order near-infrared wavefront sensor. Particular objectives of
our study were the specification of the near-infrared detector in combination with a standard wavefront sensing
system. In this paper we present the preliminary design of a Shack-Hartmann wavefront sensor operating in
the near-infrared wavelength range, which is capable of measuring the wavefronts of four telescopes simultaneously.
We further present results of our design study, which aimed at providing a first instrumental concept for
We discuss the effect of atmospheric dispersion on the performance of a mid-infrared adaptive optics assisted
instrument on an extremely large telescope (ELT). Dispersion and atmospheric chromaticity is generally considered
to be negligible in this wavelength regime. It is shown here, however, that with the much-reduced diffraction
limit size on an ELT and the need for diffraction-limited performance, refractivity phenomena should be carefully
considered in the design and operation of such an instrument. We include an overview of the theory of refractivity,
and the influence of infrared resonances caused by the presence of water vapour and other constituents in
the atmosphere. 'Traditional' atmospheric dispersion is likely to cause a loss of Strehl only at the shortest wavelengths
(L-band). A more likely source of error is the difference in wavelengths at which the wavefront is sensed
and corrected, leading to pointing offsets between wavefront sensor and science instrument that evolve with time
over a long exposure. Infrared radiation is also subject to additional turbulence caused by the presence of water
vapour in the atmosphere not seen by visible wavefront sensors, whose effect is poorly understood. We make
use of information obtained at radio wavelengths to make a first-order estimate of its effect on the performance
of a mid-IR ground-based instrument. The calculations in this paper are performed using parameters from two
different sites, one 'standard good site' and one 'high and dry site' to illustrate the importance of the choice of
site for an ELT.
AstraLux is the Lucky Imaging camera for the Calar Alto 2.2-m telescope, based on an electron-multiplying
high speed CCD. By selecting only the best 1-10% of several thousand short exposure frames, AstraLux provides
nearly diffraction limited imaging capabilities in the SDSS i' and z' filters over a field of view of 24×24 arcseconds.
By choosing commercially available components wherever possible, the instrument could be built in short time
and at comparably low cost. We present the instrument design, the data reduction pipeline, and summarise the
performance and characteristics.
Two teams of scientists and engineers at Max Planck Institut fuer Extraterrestrische Physik and at the European Southern Observatory have joined forces to design, build and install the Laser Guide Star Facility for the VLT.
The Laser Guide Star Facility has now been completed and installed on the VLT Yepun telescope at Cerro Paranal. In this paper we report on the first light and first results from the Commissioning of the LGSF.
In this paper we present an overview of the construction and implementation of the unmodulated infrared pyramid wavefront sensor PYRAMIR at the Calar Alto 3.5 m telescope. PYRAMIR is an extension of the existing visible Shack-Hartmann adaptive optics system ALFA, which allows wavefront sensing in the near-infrared wavefront regime. We describe the optical setup and the calibration procedure of the pyramid wavefront sensor. We discuss possible drawbacks of the calibration and show the results gained on Calar Alto.
We present the adaptive optics assisted, near-infrared VLTI instrument - GRAVITY - for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. Precision astrometry and phase-referenced interferometric imaging will realize the most advanced vision of optical/infrared interferometry with the VLT. Our most ambitious science goal is to study motions within a few times the event horizon size of the Galactic Center massive black hole and to test General Relativity in its strong field limit. We define the science reference cases for GRAVITY and derive the top level requirements for GRAVITY. The installation of the instrument at the VLTI is planned for 2012.
We built an optical system that emulates the optical characteristics of an 8m-class telescope like the VLT and that
contains rotating glass plates phase screens to generate realistic atmosphere-like optical turbulence. Together
with an array of single mode fibers fed from white light sources to simulate various stellar configurations, we can
investigate the behavior of different single or multi-conjugate adaptive optics setups. In this paper we present
the characteristics of phase screens etched on glass plates surfaces obtained from Silios Technologies.
PYRAMIR is a pyramid wavefront sensor (PWFS) for the 97-actuator AO system installed on the Calar Alto 3.5 m
telescope. With its linear pupil sampling of 18 pixels, its maximum loop frequency of 140 Hz, and its sensing
wavelength range from 1.1 micron to 2.4 micron it should be able to deliver reasonably high Strehl ratios at the sensing
wavelength. This feature is still unique in the world of pyramid sensors. The first on-sky test of the system was carried
out in March 2006. In this paper we will present the first results of this test. Strehl measurements medium atmospheric
conditions, using reference stars of mJ=8mag and mJ=4 mag and were performed during this first on-sky run. A detailed
comparison to simulation results will also be presented in order to confirm whether the system works up to expectances.
While this experiment has not yet the potential to show for the very first time the superiority of the pyramid principle
over corresponding Hartmann-Shack systems in a real telescope environment, it was confirmed that PYRAMIR
performs up to expectances and a detailed comparison to the Shack-Hartmann system can be carried out in the next run.
For applications like direct imaging detections of Exo-Planets from the ground e.g. in the CHEOPS project, extreme adaptive optics (XAO) systems using DMs with > 1000 actuators and correction frequencies of ~2kHz are proposed to be used in combination with coronographic devices. If the XAO and science channel work at the same wavelength it is a natural idea to combine the coronograph with the XAO's beam splitter (BS) to make use of the light that would otherwise just be lost. However, the location of the BS in the focal plane and the severe field limitation of the AO by a small (~0.3'') aperture in the focal plane imposes a spatial filtering on the wavefront sensor signal. In this paper, we examine the effect of the spatial filter on the "AO control radius" and the Strehl ratio provided by the system in a semi-analytical way, numerical simulations for various wavefront sensor types and a laboratory verification experiment.
We present in this paper the results of laboratory tests on the detector system for PYRAMIR, the infrared wavefront sensor for ALFA, the Adaptive Optics system at Calar Alto Observatory. PYRAMIR will use, at least in a first phase, a Hawaii-I detector, with 4 512x512 pixels2 quadrants which are read-out in parallel on 4 independent output channels. Since wavefront sensing in the infrared requires high frame rates and since the signal of the pyramid
wavefront sensor is distributed on a small fraction of the detector area, the detector is operated in a windowed mode. Setting the
pixel clock to the fastest speed supported by the chip without a significant increase in read noise and by addressing a 64x64 window, for instance, we are able to reach frame rates in excess of 150 Hz. We show our measurements of total read noise obtained at this relatively high read-out speed, as well as the results of our tests concerning linearity and sensitivity. The results show that
the noise introduced by the read-out electronics itself is negligible compared with the intrinsic read-noise of the detector.
In order to maximize the read-out efficiency we use differential measurements on a sequence of non destructive read-outs. We discuss the main characteristics of the detector when operating in this mode.
The performance of adaptive optics systems for existing as well as future giant telescopes heavily depends on the number of active wavefront compensating elements, the spatial, and the temporal sampling of the distorted incoming wavefront. In a phase-A study for an extreme adaptive optics system for the VLT (CHEOPS) as well as for LINC-NIRVANA a fizeau interferometer aboard LBT with a multi-conjugated adaptive optics system, we investigate how today's off-the-shelf computers compare in terms of floating point computing power, memory bandwidth, input/output bandwidth and real-time behavior. We address questions like how level three cache can impact the memory bandwidth, what matrix-vector multiplication performance is achievable, and what can we learn from standard benchmarks running on different architectures.
Extreme adaptive optics (XAO) systems are highly specialized systems
to achieve very high Strehl numbers on comparatively small fields of
view, e.g. for high-contrast applications like planet finding. We
present a study of an XAO system using a pyramid wavefront sensor
on telescopes of 8m aperture diameter and above. We used standard
(CAOS) and custom numerical simulation tools to examine the influence
of the number of basis functions in a modal correction model,
the control loop frequency of the XAO system, and atmospheric
Deformable mirrors with more than 1000 actuators are currently being
developed for eXtreme AO applications, either for ELTs, high order
Adaptive Optics correction in the visible light, or combination of
both. The large number of actuators, the high frequency at which
these DMs are to be used and further advancement in schemes for AO
control, requiring a growing degree of knowledge of the AO system
for efficient correction, sets special requirements on the
characterization of the static and dynamic behavior of the DM. In
the light of CHEOPS, an extreme-AO Planet Finder project, we have
characterized a Xinetics deformable mirrors with 349 actuators.
This mirror serves as a proxy for the characterization of a >1200
actuator DM of a similar type, which will be implemented in CHEOPS.
In this paper we present the results of this characterization.
Special attention was paid to mirror properties like hysteresis,
non-linearity, temperature dependence and influence function.
A new wavefront sensor based on the pyramid principle is being built at MPIA, with the objective of integration in the Calar Alto adaptive optics system ALFA. This sensor will work in the near-infrared wavelength range (J, H and K bands). We present here an update of this project, named PYRAMIR, which will have its first light in some months. Along with the description of the optical design, we discuss issues like the image quality and chromatic effects due to band sensing. We will show the characterization of the tested pyramidal components as well as refer to the difficulties found in the manufacturing process to meet our requirements. Most of the PYRAMIR instrument parts are kept inside a liquid nitrogen cooled vacuum dewar to reduce thermic radiation. The mechanical design of the cold parts is described here. To gain experience, a laboratory pyramid wavefront sensor was set up, with its optical design adapted to PYRAMIR. Different tests were already performed. The electronic and control systems were designed to integrate in the existing ALFA system. We give a description of the new components. An update on the future work is presented.
A study of the scintillation effects on the PSF halo of the high-contrast imaging instrument (CHEOPS) for direct exo-planet detection from the ground is presented. The fundamental goal of our analysis is to quantify the perturbations induced by the amplitude (scintillation) variations compared to those induced by the phase variations of a perturbed wavefront. Simulations of amplitude and phase screens are obtained for different seeing conditions and for a wavefront propagating at different zenith angles. For all cases a set of simulations of the PSFs in the ideal mirror-limited case (perfect AO-system) and an estimation of the detection limit Δm vs. angular separation obtained with and without scintillation are presented. The whole study is made in I-band (λ = 0.9 μm) i.e. the centered wavelength of the CHEOPS polarimetric imager. A maximum loss of contrast (obtained with and without scintillation) of ~ 25% over a FOV of 5 arcsec is found in the speckle noise-limited regime and of ~ 18% in the photon noise-limited regime. Results are discussed and conditions in which the scintillation effects cannot be neglected are investigated.
The calibration process for an adaptive optics system using modal control computes the reconstructor matrix in terms of a matrix whose columns are the measurements from a wavefront sensor. Each column of wavefront sensor measurements corresponds to a mode that is applied to the mirror. Since the measured gradients are corrupted by errors, the accuracy of the computed reconstructor is degraded by large condition numbers of the gradient matrix. A common method used to limit the condition number of this matrix is to reject all higher order modes when the condition number reaches the maximum desired value. However, it is possible (even likely) that one or a few modes are responsible for much of the increase in the condition number. By rejecting only those modes, an increased number of modes could be controlled. Unfortunately, computing the condition number of the gradient matrix for all possible combinations of modes is prohibitive.
This paper uses a genetic optimization algorithm to increase the number of modes that are retained for control. The genetic algorithm maximizes the number of modes retained. A bound on the condition number of the gradient matrix is imposed. The paper applies this method to both the ALFA adaptive optics system on Calar Alto (with 37 subapertures), and a proposed CHEOPS adaptive optics system with 1652 subapertures.
We present results from a phase A study supported by ESO for a VLT instrument for the search and investigation of extrasolar planets.
The envisaged CHEOPS (CHaracterizing Extrasolar planets by Opto-infrared Polarization and Spectroscopy) instrument consists of an extreme AO system, a spectroscopic integral field unit and an imaging polarimeter. This paper describes the conceptual design of the imaging polarimeter which is based on the ZIMPOL (Zurich IMaging POLarimeter) technique using a fast polarization modulator combined with a demodulating CCD camera. ZIMPOL is capable of detecting polarization signals on the order of p=0.001% as demonstrated in solar applications. We discuss the planned implementation of ZIMPOL within the CHEOPS instrument, in particular the design of the polarization modulator. Further we describe strategies to minimize the instrumental effects and to enhance the overall measuring efficiency in order to achieve the very demanding science goals.
The CHEOPS Planet Finder is one of the proposed second generation instruments for the VLT. Its purpose is to image and characterize giant extrasolar planets in different phases of their evolution: young, warm planets as well as old, cold ones. Imaging the last ones is the most challenging task because of the very large (>108) flux contrast with their star. Detection of such faint sources close to the stars from the ground requires a very high Strehl ratio and efficient suppression of the speckle noise. Two complementary strategies, based on imaging polarimetry using fast modulation and on integral field spectroscopy, are included as scientific channels of CHEOPS, after the high order adaptive optics module. The outputs of the two channels will allow a close insight into the main properties of detected extrasolar planets. In
addition, the CHEOPS instrument is well suited for a number of astrophysical projects, which are briefly described.
We are currently investigating the possibilities for a high-contrast, adaptive optics assisted instrument to be placed as a 2nd-generation instrument on ESO's VLT. This instrument will consist of an 'extreme-ao' system capable of producing very high Strehl ratios, a contrast-enhancing device and two differential imaging detection systems. It will be designed to collect photons directly coming from the surface of substellar companions - ideally down to planetary masses - to bright, nearby stars and disentangle them from the stellar photons. We will present our current design study for such an instrument and
discuss the various ways to tell stellar from companion photons. These ways include the use of polarimetric and/or spectroscopic
information as well as making use of knowledge about photon statistics. Results of our latest simulations regarding the instrument will be presented and the expected performance discussed.
Derived from the simulated performance we will also give details
about the expected science impact of the planet finder. This will
comprise the chances of finding different types of exo-planets -
notably the dilemma of going for hot planets marginally separated
from their parent stars or cold, far-away plamnets delivering very
little radiation, the scientific return of such detections and
follow-up examinations, as well as other topics like star-formation,
debris disks, and planetary nebulae where a high-resolution,
high-contrast system will trigger new break-throughs.
Detection of faint companions near bright stars requires the usage of high dynamic range instrumentation. The four quadrant phase mask is a quite efficient nulling device for the light of on-axis stars as shown by simulations. We conducted a test of the true performance of this concept starting with the manufacturing of the optical element, continuing with the installation in the telescope and the usage of the Adaptive Optics system. A four quadrant phase mask was installed in the 3.5m telescope on Calar Alto and several tests with both an artificial source and natural stars were conducted. Tests in order to detect faint companions around HD 140913, TRN 1 and HD 161797 were successful for the last target and also, although almost serendipitously, in the case of HD144004. The main limitations found for the phase mask cancelling effect at relatively low Strehl ratios (16%-63%) were the residual tip-tilt of our system and the control of placement of the mask in the optical train.
For the successful operation of laser referenced adaptive optic systems very powerful lasers for the creation of sodium guide stars are necessary. Here we introduce the design of PARSEC, the cw sodium-line laser for the VLT, and present out first laboratory results on the performance of the system. So far we have achieved a stable output power of 12.8W in a single spatial mode and a single frequency.
An important requirement for the VLT Laser Guide Star Facility is the ability to measure the centroid height of the atmospheric sodium layer, located at an altitude of about 90km, to an accuracy of 200m. In this paper, we describe the sodium profiler system designed to achieve this and the expected performance.
In this paper, we review the salient facts for a range of available atmosphere emulation technologies, and in the framework of the ESO Multi-Conjugate-AO demonstrator project, aptly called MAD, we present our phase screen test results for silver-sodium ion-exchange, transmissive phase screens. We find (a) that the measured power spectrum of phase fluctuations is consistent with the input Von Karman spectrum and (b) that by tracking the best focus of ten spots formed by a silver-sodium ion-exchange micro-lens array, it was found that the wavelength dependence of 1.266μm of phase-shift is 1.5±2.5% relative to air in the wavelength range 550nm to 800μm.
Additionally, we present our optical design and specifications for MAPS, the Multi-Atmospheric Phase screens and Stars instrument that will be used to test MAD before shipment to the VLT. It includes glass screens conjugate to the 0.25km, 3.0km, and 9.0km atmospheric layers above the telescope. We explain the reasoning behind the choice of pupil size and implications for phase screen proximity, footprint sizes, and wind speed gradients. Our design mimics the VLT Nasmyth F/15 focal plane in terms of plate scale, field of view, high Strehl, and field curvature.
One of the critical design drivers for the PARSEC laser was that by the time it is integrated into the VLT Laser Guide Star Facility in 2003 it should be able to run remotely without any hands-on tuning for a period of at least one week. In this contribution we describe some of the methods we have employed to achieve this and take a brief look at the proposed operating procedure.
We report on the ongoing VLT Laser Guide Star Facility project, which will allow the ESO UT4 telescope to produce an artificial reference star for the Adaptive Optics systems NAOS-CONICA and SINFONI. A custom developed dye laser producing >10W CW at 589nm is installed on-board of the UT4 telescope, then relayed by means of a single mode optical fiber behind the secondary mirror, where a 500mm diameter lightweight, f/1 launch telescope is projecting the laser beam at 90 km altitude.
We described the design tradeoffs and provide some details of the chosen subsystems. This paper is an update including subsystems results, to be read together with our previous paper on LGSF design description.
Shack-Hartmann based wavefront sensors, used to compensate atmospheric turbulence, appear to be less sensitive than cur-vature based wavefront sensors by more than a magnitude. Besides their read noise free APD detectors and different meas-urement principle, the sensitivity of curvature sensors may benefit from the keystone shaped lenslet geometry which opti-mally balances aperture coverage and illumination of individual subapertures. This paper describes the implementation of a keystone shaped lenslet array for the ALFA Shack-Hartmann based AO system. We compare the novel design with hexago-nal shaped lenslets under different operating conditions such as selected modal basis set and number of compensated modes theoretically and in practice.
Multiconjugate adaptive optics employing several deformable mirrors conjugated at different altitudes has been proposed in order to extend the size of the corrected field of view [FOV] with respect to the size of the corrected FOV given by a classical adaptive optics system. A three dimensional measurement of the turbulent volume is needed in order to collect the information to command the several deformable mirrors. Given a set of guide stars in the field of view, this can be done both using tomography, in which several wavefront sensors are used, each of them coupled to one of the guide stars, or layer oriented techniques, in which wavefront sensors are coupled to a given layer in the atmosphere, and collect light from the whole set of guide stars. We will call this type of measurements optical layer oriented. This type of measurements can be also obtained combining in a numerical way, tomographic measurements. This hybrid approach is called numerical layer oriented. In order to compare their performance, we present an analytical study of the signal to noise ratio [SNR] in the measurements for the two techniques. Optical layer oriented is shown to be more efficient in the range of faint flux and large number of guide stars, while low detector noise will allow numerical layer oriented schemes to be more efficient in terms of SNR.
The objective of the PYRAMIR project is to complement the Calar Alto Adaptive Optics System - ALFA - with a new pyramid wavefront sensor working in the near IR, replacing the previous tip-tilt tracker arm. Here we describe the Science as well as the Technical motivation for such a system. The optical design will be presented, discussing the particular requirements posed by sensing the wavefronts in the infrared like a cooling system for the opto-mechanical components, etc. We will also talk about the components, like the IR detector we plan to use - PICNIC, as one option, the sucessor of NICMOS3 from Rockwell, together with the AO-Multiplexer. It is described how we expect to integrate the system into the optical, machanical, electronical and control architecture of ALFA.
Multi-Conjugate Adaptive Optics (MCAO) is working on the principle to perform wide field of view atmospheric turbulence correction using many Guide Stars located in and/or surrounding the observed target. The vertical distribution of the atmospheric turbulence is reconstructed by observing several guide stars and the correction is applied by some deformable mirrors optically conjugated at different altitudes above the telescope.
The European Southern Observatory together with external research institutions is going to build a Multi-Conjugate Adaptive Optics Demonstrator (MAD) to perform wide field of view adaptive optics correction. The aim of MAD is to demonstrate on the sky the feasibility of the MCAO technique and to evaluate all the critical aspects in building such kind of instrument in the framework of both the 2nd generation VLT instrumentation and the 100-m telescope OWL.
In this paper we present the conceptual design of the MAD module that will be installed at one of the VLT unit telescope in Paranal to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band.
We present the design of and recent results from the Large Binocular Telescope (LBT) facility SCIDAR. To our knowledge, this work will produce the first SCIDAR designed as a user instrument for routine seeing measurements in support of telescope operations. Using a commercial, off-the-shelf approach, we have minimized the resources required for system construction.
8m class telescopes offer an extremely powerful tool for astronomical research. The light collecting power is enormous and with the combination of adaptive optics and laser guide stars astronomy will make a big step forward in knowledge in almost any field. For the creation of artificial laser-based guide stars that make use of the sodium layer in the earth atmosphere, very powerful lasers at 589nm are necessary. We introduce here the PARSEC laser that will be installed at the UT4 telescope of the VLT, in Chile. This laser will emit cw radiation at more then 10W output power and offers a scalability in power for future multi guide star systems.
We present results of simultaneous measurements of atmospheric parameters using a SCIDAR instrument and the Calar Alto ALFA adaptive optics (AO) system. First results indicated that SCIDAR measurements can indeed be useful for selecting appropriate closed-loop settings of an AO system. We will further establish this assumption by presenting the fully reduced data sets showing the time series of the Fried parameter and the isoplanatic angle as obtained from the two instruments. The data was recorded under varying seeing conditions on a binary star and an open cluster. Additionally, we will point out possible applications of simultaneous SCIDAR measurements in AO observations and systems.
Observations have shown the presence of sodium layer centroid height variations of a few hundred meters on timescales of tens of seconds. As quality laser guide star (LGS) plus adaptive optics (AO) assisted astronomy, especially on large (8m+) telescopes, will require optimal scheduling of observations and regular laser and wavefront sensor focusing at sites where sporadic sodium layers are frequent, an 'easy to use' sodium layer monitor is required. LIDAR offers a convenient means to achieve this. By pulsing the outgoing sodium laser and performing time-of-flight measurements on the returned photons we can acquire the altitude profile of the sodium layer. Unfortunately, conventional LIDAR requires the laser duty cycle to be very low, therefore large integration times are required. However, by using a cross-correlation technique the duty cycle can be increased to 50%, which gives far better performance. We present the details of this technique which involved amplitude modulation of the MPIA/MPE ALFA cw laser, as well as the following results of such LIDAR measurements performed in October 1999 at the 3.5 m telescope at Calar Alto Observatory in Spain. The altitude of the sodium layer at Calar Alto on 17th and 18th October 1999 was found to be at 90 +/- 3 km and there is evidence for sporadics on one of two nights with sporadic layer FWHM* varying from approximately 240 to 350 m. In addition, a noticeable layer FWHM change (excluding the sporadic layer) from approximately 13 to approximately 5 - 7 km was observed over the two nights. After flux and altitude calibration and correction of the projected altitude range, a very good agreement is found between sodium layer profiles derived from an auxiliary telescope and 3.5 m telescope LIDAR observations. Using an intensity weighted centroid algorithm the centroid height of the sodium layer was observed to have a variation of < 500 m in approximately 10 minutes. Although, shorter timescale variations may be have been present, poor observing conditions and resulting reduced S/N prevents this analysis.
In this paper, we discuss the benefits of ground-based, adaptive optics (AO) aided observations for star formation research. After outlining the general advantages, we present results obtained during the ALFA science demonstration program in 1999. These results underline the absolute necessity of AO assistance for almost any kind of observations regarding star formation regions.
The Max-Planck institutes for astronomy and for extraterrestrial physics run a high order adaptive optics system with a laser guide star facility at the Calar Alto 3.5- m telescope in southern Spain. This system, called ALFA, saw first light in September 1996. Today, ALFA can compensate for atmospheric turbulences with natural guide stars as faint as 13.5th magnitude in R-band. ALFA recently succeeded in overcoming this limiting magnitude with the deployment of its laser guide star. This paper briefly reviews the ALFA project and its progress over the last 3 years. We further discuss the impact of sodium-layer laser guide stars on wavefront sensing and present results obtained with both kinds of guide stars.
MIDI is a two channel mid-infrared interferometric instrument developed for the Very Large Telescopes (VLT) Interferometer (VLTI). A control system with real-time capabilities integrates the various VLTI subsystems. Based on the VLTI control architecture and its interferometric extension, the VLTI control system, the MIDI control system will use synchronized VME computers running Tornado to control time critical subsystems such as delay lines and detector control electronics. Standard Unix workstations run high-level coordinating, monitoring, and data pre-processing tasks as well as graphical user interfaces. We describe the MIDI control architecture, the data flow and storage concept, and the self fringe tracking option. Furthermore we introduce a software package currently under development to simulate observations with MIDI.
The MPIA/MPE adaptive optics with a laser guide star system ALFA works excellent with natural guide stars up to 13th magnitude in R-band. Using fainter natural guide stars or the extended laser guide star, ALFA's performance does not entirely satisfy our expectations. We describe our efforts in optimizing the wavefront estimation process. Starting with a detailed system analysis, this paper will show how to construct a modal basis set which efficiently uses Shack- Hartmann measurements while keeping a certain number of low order modes close to analytical basis sets like Zernikes or Karhunen-Loeve functions. We will also introduce various phase estimators (least squares, weighted least squares, maximum a posteriori) and show how these can be applied to the ALFA AO. A first test done at the Calar Alto 3.5-m-telescope will be discussed.
The Max-Planck-Institutes for Astronomy and for Extraterrestrial Physics (MPE) have recently installed a laser guide star (LGS) adaptive optics (AO) system at the 3.5m telescope on Calar Alto in Spain. The AO system consists of a Shack-Hartmann sensor, a deformable mirror with 97 actuators, and a wave-front processor that allows closed loop operations of up to 1200 Hz. As a first step we closed the high order AO loop on bright natural guide stars. As a second step we closed the AO loop ALFA's design, operation, and upgrade plans.
The 3.8 m UK Infrared Telescope has been the focus of a program of upgrades intended to deliver images which are as close as possible to the diffraction limit at (lambda) equals 2.2 micrometers (FWHM equals 0.'12). This program is almost complete and many benefits are being seen. A high-bandwidth tip-tilt secondary mirror driven by a Fast Guider sampling at <EQ 100 Hz effectively eliminates image movement as long as a guide star with R < 16.m5 is available within +/- 3.'5 of the target. Low-order active control of the primary mirror and precision positioning of the secondary, using simple lookup tables, provide telescope optics which are already almost diffraction limited at (lambda) equals 2 micrometers . To reduce facility seeing the dome has been equipped with sixteen closable apertures to permit natural wind flushing, assisted in low winds by the building ventilation system. The primary mirror will soon be actively cooled and the concrete dome floor may be thermally insulated against daytime heating if fire safety concerns can be resolved. Delivered images in the K band now have FWHM which is usually <EQ 0.'8, frequently <EQ 0.'6 and quite often approximately 0.'3. Examples of the latter are shown: these approximate the resolution achieved by NICMOS on the HST. We estimate that the productivity of the telescope has approximately doubled, while its oversubscription factor has increased to > 4.
All the major components of the United Kingdom Infra-Red Telescope (UKIRT) Upgrades program are now in place. The thrust of the program has shifted to developing the new telescope capabilities so that performance is maintained under real observing conditions. This paper presents an overview of the current state of affairs and focuses on how we have implemented the secondary mirror and fast guide systems and how we control the active primary mirror system to minimize the telescope aberrations.
The 3.8 m UK infrared telescope (UKIRT) is currently the focus of an upgrades program to improve its imaging performance, ideally to approach its diffraction limit in the near-IR at 2.2 micrometer, with FWHM approximately 0.'12. This program is now in its late stages. All the new systems have been designed, most have been manufacture and many have been installed. A new top end carries an adaptive tip-tilt secondary mirror with active precision alignment, which, with low-order active control of the primary mirror, should provide the desired intrinsic optical performance. The adaptive tip- tilt system will correct image motion from telescope vibrations and drive errors and from atmospheric wavefront tilt; delivered images are expected regularly to be less than 0.'5 over wide fields, and within a factor 2 or so of the diffraction limit, at least inside an isoplanatic patch of order an arcmin radius. To reduce facility seeing the primary mirror has been equipped with a ventilation system and will receive a 5 kW cooling system; the dome is being equipped with sixteen closable apertures to permit natural wind flushing, which can be assisted by the building air handling system in low winds. It is hoped that facility seeing -- excluding boundary layer effects -- will be imperceptible during approximately 85% of observable time. The upgraded UKIRT should be well capable of exploiting fully the very best conditions on Mauna Kea.
The United Kingdom Infra-Red Telescope (UKIRT) is currently undergoing its first major upgrade since its construction. The upgrades program consists of an adaptive tip-tilt and focus system closed with a CCD system at rates of up to a few hundred hertz, an active primary support system, extensive dome thermal work, and other miscellaneous improvements. This paper outlines how we propose to control the new systems, and how these systems are integrated into the existing telescope control system.
This is a progress report on the development of the tip-tilt secondary mirror for the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. The concept-- with emphasis on the electromechanical and optomechanical design--was published in an earlier paper. The reader is kindly requested to refer to the background information given there. Here, we present the electronics, system control and data handling considerations along with updated design drawings of the mirror and the combined piezoelectric/hexapod mirror mounts.
This paper describes the basic design, operation, and initial performance of MAGIC, the new MPI fur Astronomie General-purpose Infrared Camera. MAGIC uses a 256 X 256 NICMOS3 HgCdTe detector array and has flexible optics and drive electronics that permit a variety of observing configurations. The camera was designed and built to MPIA specifications by Infrared Laboratories of Tucson, Arizona. MAGIC is based at the 3.5 meter telescope on Calar Alto, although it may be used at a number of other sites, including the 2.2 and 1.2 meter telescopes on Calar Alto and the 2.2 meter MPIA/ESO telescope at La Silla. The design of MAGIC places particular emphasis on wide field, deep imaging at the f/10 focus of the 3.5 m telescope and on providing some spectroscopic and speckle interferometric capability.