The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) is a direct imaging experiment designed to observe exozodiacal dust and debris disks that orbit nearby stars from a high-altitude balloon platform. The experiment consists of a vector vortex coronagraph and a multi stage adaptive optics system with multiple wavefront sensors and two deformable mirrors. This paper details the hardware and software implementation of one of the DM interfaces used in the PICTURE-C low-order wavefront control system. We discuss the algorithm used to drive a commercial o_-the-shelf DM with an actuation resolution of 14-bits to meet the PICTURE-C requirement of 16-bits. The algorithm utilizes fast temporal dithering in the form of pulse density modulation to reduce the quantization error of the DM actuation. The described DM control mechanism can operate at a framerate of ~500 Hz with an equivalent actuation resolution of 16-bits with minimal computational load on the deployed processor.
The performances of high resolution magnetic deformable mirrors have been recently improved: the mechanical bandwidth has been increased to 2 kHz, and a fast stroboscopic Shack-Harman wavefront was used to measure a settling time as low as 400μs. Recent improvements in the substrate-thinning processes made possible the availability of large, high-quality membranes compatible with deformable mirrors. Prototype testing and simulations show that devices with up to 60x60 actuators are now possible. For open-loop operations, a novel feed-forward algorithm was developed to compensate for residual creeping and improve the DM stability to below10nm RMS over 6 hours.
An adaptive optics system running at 1500 Hz was integrated using commercially available components. The deformable mirror was made by Alpao and has 277 actuators on a 1:5mm pitch. The wavefront sensor is based on the OCAM2 EMCCD (Electron-multiplying charge-coupled device) camera from First Light Imaging and a 20×20 lenslet array. We present an initial system integration phase using the Alpao Core Engine toolbox running in a Matlab® environment. During the second integration phase, benchmark tests for Alpao's real-time controller ACEfast show the possibility to obtain a pure delay of τ = 130 µs in a parallel worker configuration with a computing power of 2 CPU/8 core + 4GPU for a problem size equivalent to state-of-the-art adaptive optics systems.
Direct imaging of exoplanet is one of the most exciting field of planetology today. The light coming from exoplanet orbiting their host star witnesses for the chemical composition of the atmosphere, and the potential biomarkers for life. However, the faint flux to be imaged, very close to the huge flux of the parent star, makes this kind of observation extremely difficult to perform from the ground. The direct imaging instruments (SPHERE , GPI ) are nowaday reaching lab maturity. Such instrument imply the coordination of XAO for atmospherical turbulence real-time correction, coronagraphy for star light extinction, IR Dual band camera, IFS, and visible polarimetry. The imaging modes include single and double difference (spectral and angular). The SPHERE project is now at the end of AIT phase. This paper presents the very last results obtained in laboratory, with realistic working conditions. These AIT results allows one to predict on-sky performance, that should come within the next weeks after re-installation at Very Large Telescope at Paranal.
Direct detection and spectral characterization of extra-solar planets is one of the most exciting and challenging areas in
modern astronomy due to the very large contrast between the host star and the planet at very small angular separations.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research in Europe) is a second-generation instrument for the
ESO VLT dedicated to this scientific objective. It combines an extreme adaptive optics system, various coronagraphic
devices and a suite of focal instruments providing imaging, integral field spectroscopy and polarimetry capabilities in the
visible and near-infrared spectral ranges.
The extreme Adaptive Optics (AO) system, SAXO, is the heart of the SPHERE system, providing to the scientific
instruments a flat wavefront corrected from all the atmospheric turbulence and internal defects. We present an updated
analysis of SAXO assembly, integration and performance. This integration has been defined in a two step process. While
first step is now over and second one is ongoing, we propose a global overview of integration results. The main
requirements and system characteristics are briefly recalled, then each sub system is presented and characterized. Finally
the full AO loop first performance is assessed. First results demonstrate that SAXO shall meet its challenging
SPHERE, the extra-solar planet imager for the Very Large Telescope is a program that has been running since 2006. The
instrument is now nearing completion and it is in the final integration stage. The 3 science instruments of SPHERE are
now complete and have passed the internal acceptance review while the complex common path with the extreme
Adaptive optics system, the coronographs and the calibration module is aggressively progressing. This paper reviews the
performance of the Common Path (CP) and three science instruments of SPHERE: IRDIS, the dual band imager; IFS, the
integral field spectrograph and ZIMPOL, the imaging polarimeter. We also present an outlook at the final system
SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the
direct detection from extra-solar planets. The instrument will search for direct light from old planets with orbital periods
of several months to several years as we know them from our solar system. These are planets which are in or close to the
habitable zone. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO
SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from
extrasolar planets. The search for reflected light from extra-solar planets is very demanding because the signal decreases
rapidly with the orbital separation. For a Jupiter-sized object and a separation of 1 AU the planet/star contrast to be
achieved is on the order of 10-8 for a successful detection. This is much more demanding than the direct imaging of
young self-luminous planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph.
SPHERE is foreseen to have first light at the VLT at the end of 2012. ZIMPOL is currently in the subsystem testing
phase. We describe the results of verification and performance testing done at the NOVA-ASTRON lab. We will give an
overview of the system noise performance, the polarimetric accuracy and the high contrast testing. For the high contrast
testing we will describe the impact of crucial system parameters on the contrast performance. SPHERE is an instrument
designed and built by a consortium consisting of IPAG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève,
ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
The MEMS deformable mirror (DM) performances have been dramatically increased during the last years. Although
adaptive optics has the potential to address many optical problems faced by engineers and scientists, it has not yet
reached all domains of applications that it might reach. In this article, we present some key changes.
The direct imaging of exoplanet is a challenging goal of todays astronomy. The light transmitted by exoplanet
atmosphere is of a great interest as it may witness for life sign. SPHERE is a second generation instrument for
the VLT, dedicated to exoplanet imaging, detection, and characterisation. SPHERE is a global project of an
European consortium of 11 institutes from 5 countries. We present here the state of the art of the AIT of the
Adaptive Optics part of the instrument. In addition we present fine calibration procedures dedicated to eXtreme
Adaptive Optics systems. First we emphasized on vibration and turbulence identification for optimization of the
control law. Then, we describe a procedure able to measure and compensate for NCPA with a coronagraphic
The SPHERE instrument aims at detecting giant extrasolar planets in the vicinity of bright stars. Such a challenging goal
requires the use of a high performance Adaptive Optics (AO) system, a coronagraphic device to cancel out the flux
coming from the star itself, and smart focal plane techniques to calibrate residual uncorrected turbulent and/or static
wavefronts. Inside the adaptive optic system, a specific tool is developed in SPHERE to ensure that the star is always
well centered on the coronagraph. This tool called Differential Tip-Tilt Sensor (DTTS) measures the position of the star
at the same wavelength than the science instruments. It is located very close to the focal plane to minimize drifts between
DTTS and the coronagraph. After describing the DTTS, we will describe the tests and laboratory results on stability
measurement of the DTTS; stability which is crucial for SPHERE performance.
ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to
detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an
extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of
2011. ZIMPOL is currently in the manufacturing, integration and testing phase. We describe the optical, polarimetric,
mechanical, thermal and electronic design as well as the design trade offs. Specifically emphasized is the optical quality
of the key performance component: the Ferro-electric Liquid Crystal polarization modulator (FLC). Furthermore, we
describe the ZIMPOL test setup and the first test results on the achieved polarimetric sensitivity and accuracy. These
results will give first indications for the expected overall high contrast system performance. SPHERE is an instrument
designed and built by a consortium consisting of LAOG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève,
ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
We present the improvement of science throughput of 1m class telescopes that can be obtained using COTS adaptive
optics. It is based on a new architecture of adaptive optics system using a new kind of magnetic deformable mirrors, a
highly sensitive EMCCD wavefront sensor and a novel real time architecture called ACE and working on a standard
It will be shown the dramatically increase of performances that can be achieved using small adaptive optics (typically
8x8 actuators) with 1m to 2m class telescopes and in particularly, we will focus our presentation of the improvement of
the science throughput thanks to this simple and efficient A.O. system
One of the main challenges to obtain the contrast of >15mag targeted by an extra-solar planet imager like SPHERE lies
in the calibration of all the different elements participating in the final performance. Starting with the calibration of the
AO system and its three embedded loops, the calibration of the non-common path aberrations, the calibration of the NIR
dual band imager, the NIR integral field spectrograph, the NIR spectrograph, the visible high accuracy polarimeter and
the visible imager all require sophisticated calibration procedures. The calibration process requires a specific extensive
calibration unit that provides the different sources across the spectrum (500-2320nm) with the stabilities and precisions
required. This article addresses the challenges met by the hardware and the instrument software used for the calibration
SPHERE, the ESO extra-solar planet imager for the VLT is aimed at the direct detection and spectral characterization of
extra-solar planets. Its whole design is optimized towards reaching the highest contrast in a limited field of view and at
short distances from the central star. SPHERE has passed its Final Design Review (FDR) in December 2008 and it is in
the manufacturing and integration phase. We review the most challenging specifications and expected performance of
this instrument; then we present the latest stage of the design chosen to meet the specifications, the progress in the
manufacturing as well as the integration and test strategy to insure gradual verification of performances at all levels.
We describe the performances obtained with the latest developments of voice-coils deformable mirrors for the correction
of atmosphere turbulence. Thanks to the electro-magnetic principle of the deformable mirror, very large strokes are
obtained (more than 20μm) with a very large bandwidth (1 kHz). We further present the ALPAO Core Engine which is
an open and flexible environment allowing fast developments of high performances adaptive optics. We emphasize all
the benefits for free space optical communication.
Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most
challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the
planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design
of a "Planet Finder" instrument is therefore optimized towards reaching the highest contrast in a limited field of view and
at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through
their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design and
expected performance of the SPHERE instrument.
Extreme adaptive optics system (SAXO) is the heart of the SPHERE instrument which aims at directly detect and characterize giant extra-solar planets from the ground. It should equip one of the four VLT 8-m telescopes at the end of 2010. We present a detailed design and architecture of the SAXO system. We focus on each critical point that has been solved during the preliminary design phase. It concerns the adaptive optics system itself but also the interaction with other SPHERE subsystems (such as coronagraphy) and focal plane instrumentation (dual band imager, integral field spectroscopy and polarimetric imager). Acceptance and integration tests of SAXO are discussed. Finally, detailed performance of the whole system and comparison to the science requirements are provided.
The SPHERE is an exo-solar planet imager, which goal is to detect giant exo-solar planets in the vicinity of bright stars
and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made
of an extreme-Adaptive Optics (AO) turbulence correction, pupil tracker and interferential coronagraphs. At its back
end, an Infra-Red Dual-beam Imaging and Spectroscopy science module and an integral field spectrograph work in
the Near Infrared (NIR) Y, J, H and Ks bands (0.95 - 2.32μm) and a high resolution polarization camera covers the
visible (0.6 - 0.9 μm) region. We describe briefly the science goals of the instrument and deduce the top-level
requirements. This paper presents the system architecture, and reviews each of the main sub-systems. The results of the
latest end-to-end simulations are shown and an update of the expected performance is given. The project has been
officially kicked-off in March 2006, it is presently undergoing Preliminary Design Review and is scheduled for 1st
light in early 2011. This paper reviews the present design of SPHERE but focuses on the changes implemented since
this project was presented the last time to this audience.
The Planet Finder instrument for ESO's VLT telescope, scheduled for first light in 2010, aims to detect giant extra-solar planets in the vicinity of bright stars and to characterise the objects found through spectroscopic and polarimetric observations. The observations will be done both within the Y, J, H and Ks atmospheric windows (~0.95 - 2.32μm) by the aid of a dual imaging camera (IRDIS) and an integral field spectrograph (IFS), and in the visible using a fast-modulation polarization camera (ZIMPOL). The instrument employs an extreme-AO turbulence compensation system, focal plane tip-tilt correction, and interferential coronagraphs. We describe briefly the science goals of the instrument and deduce the top-level requirements. The system architecture is presented, including brief descriptions of each of the main sub-systems. Expected performance is described in terms of end-to-end simulations, and a semi-analytic performance-estimation tool for system-level sensitivity analysis is presented.
We present here a deformable mirror (DM) with a continuous mirror using new zipping actuators, compatible with a simplified collective process and electronic integration. The originality of these new zipping actuators is the presence of a rotation support and a lever to push the mirror. Therefore a small electrostatic gap is enough to obtain large strokes. The device is a bi-directional electrostatic actuator with two other adjacent levers which pull the mirror down. The mirrors are silicon reflective membranes obtained with SOI wafers to bring flexibility in the mechanical design, as well as superior mirror flatness and surface roughness. Using finite element analysis (FEA), simulations is being performed so as to evaluate the performance of the actuators. The recent simulations have shown that the actuator design should enable inter-actuator strokes larger than 1 μm. A first device has been realised to show the feasibility. It is DMs with 19 actuators and a mirror of 1 cm in diameter. Experimentally observed actuator strokes of more than 4.5 μm were obtained for an applied voltage of 60 V when the mirror was pulled down and the first promising results were obtained when the mirror was pushed up from 10 V to 80 V. The specific shape of the links between the membrane and the actuators provides remarkable optical properties. The optical print-through due to the pillar architecture has been reduced to 1.5 nm RMS, which is close to the mirror roughness.
After more than two years of very successful operation in NGS mode, the VLT Shack-Hartmann AO system NAOS will be upgraded to be operational with the VLT LGS in late 2004. The implementation concerns a new STRAP tip-tilt sensor, an optical path including the trombone to accommodate for LGS height variations, a LIDAR device to measure the initial LGS height, and many high and low level software changes (real-time computer, instrument control, templates, preparation software, etc.). The paper presents this upgrade concept as well as some analysis of the predicted performance of NAOS-LGS.
An on-line estimation of turbulence parameters (r0, L0 and wind speed) and Adaptive Optics (AO) performance using NAOS [Nasmyth Adaptive Optics System] is presented. The method is based on the reconstruction of open-loop data from deformable mirror voltages and residual wavefront sensor slopes obtained in closed loop. This dedicated tool implemented in the real time computer of the NAOS system (first AO of the Very Large Telescope) allows without any loop opening to automatically monitor and display (every 15 seconds) both the atmospheric conditions and the system performance. We have validated the algorithm and tested its robustness on simulated and experimental data (both in laboratory and on sky). Using data obtained during more than two years of operations, statistical study on NAOS performance and turbulence characteristics are proposed. An on-line estimation of turbulence parameters (r0, L0 and wind speed)
and Adaptive Optics (AO) performance is presented.
Observing at high angular resolution from the ground is not made possible with Adaptive Optics alone, and besides the turbulence residuals, atmospheric refraction, thermal background or instrument's mechanical flexures may also severely limit the gain of optical quality that AO techniques are supposed to provide. We describe here how NAOS, the newly installed AO system on the VLT, has been designed to accommodate for these unavoidable effects. In particular, beam chopping, flexures compensation and AO tracking on reference objects with a significant relative motion will be addressed. It will thus be shown how long term astronomical observations at the diffraction limit can be carried out with an AO system under regular ground level conditions, thanks to the implementation of original technical solutions.
Only a very few examples of near-infrared wavefront sensors can be found in the litterature. However, none of these sensors provide routine observation yet. Our sensor is the only one to be operated routinely on a large AO system. Entirely cryogenized, this sensor is built around a so-called HAWAII array from Rockwell (HgCdTe, 1024×1024). It is working in the huge spectral band ranging from 0.8 to 2.55 microns, and may use -when required- all the flux from this very whole band. It allows to switch between several optical configurations in order to match all atmospheric and observing conditions, while its original mechanical design allows to keep, even at cryogenic temperatures, a mechanical stability lower than 4 microns in any position. It also has some particular read-out schemes, allowing to obtain frame rates as high as 1200 Hz while keeping a read-out noise performance of 10 electrons rms/pixel. The analysis of the design parameters (pixel size, field of view) is exposed in this article. Some results, obtained during the comissioning runs at ESO, will also be presented.
NAOS is the first adaptive optics system installed at the VLT 8m telescopes. It was designed, manufactured and tested by a french Consortium under an ESO contract, to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 μm spectral range. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR spectral range. It has been installed in November at the Nasmyth focus B of the VLT UT4. During the first light run in December 2001, NAOS has delivered a Strehl ratio of 50 under average seeing conditions for bright guide stars. The diffraction limit of the telescope has been achieved at 2.2 μm. The closed loop operation has been very robust under bad seeing conditions. It was also possible to obtain a substantial correction with mV=17.6 and mK=13.1 reference stars. The on-sky acceptance tests of NAOS-CONICA were completed in May 2002 and the instrument will be made available to the European astronomical community in October by ESO. This paper describes the system and present the on-sky performance in terms of Strehl ratio, seeing conditions and guide star magnitude.
The NAOS adaptive optics system was installed in December 2001 on the Nasmyth focus of the ESO VLT. It includes two wavefront sensors: one is working at IR wavelength analysis and the other at visible wavelengths. This paper describes the NAOS Visible Wave Front Sensor based on a Shack-Hartman principle and its performances as measured on the sky. This wavefront sensor includes within a continuous flow liquid nitrogen cryostat:
1) a low noise fast readout CCD camera controlled by the ESO new generation CCD system FIERA using a fast frame rate EEV/Marconi CCD-50 focal plane array. This 128×128 pixels focal plane array has a readout noise of 3 e- at 50 kilopixel/sec/port. FIERA provides remotely controlled readout modes with optional binning, windowing and flexible integration time.
2) two remotely exchangeable micro-lens arrays (14×14 and 7×7 micro-lenses) cooled at the CCD temperature ( -100 °C) within the cryostat. The CCD array is directly located in the micro lenses focal plane at a few millimeters apart without relay optics.
3) Additional opto-mechanical functions are also provided (atmospheric dispersion compensator, flux level control, field of view limitation).
On sky performances of the wavefront sensor are presented. Adaptive Optics corrections was obtained with a reference star as faint as a visible magnitude 17 with a band-path of 40 Hz in close loop.
Electrostatically actuated micro-mirrors represent one of the most promising technologies for future adaptive optics systems. Due to their relatively high prototyping cost and long fabrication cycle, simulation is one of the key points of their design and optimization. Finite element analysis, behavioral modeling and electronic CAD packages are generally used to study each part of the mirror. This paper shows how the emerging VHDL-AMS language can be used to combine all these simulation tools, and obtain a dynamical simulation of the complete micro-mirror device. This model can then be used as a tool to optimize the characteristics of the mirror and its control electronics to match the specifications of various adaptive optics systems.
The application of adaptive optics in astronomy requires increasingly compact deformable optical components with a high density of actuators, able to provide strokes of several micrometers. The main problem of the use of adaptive optics in more mainstream areas is the cost, the size and consequently the weight of the system. This paper presents the design and the results obtained with the deformable mirror under development. The system will have a continuous reflective membrane of 1 cm2 driven by 64 closing gap actuators operating in contact. In the following this type of actuators is called “zipping actuators”. Applying 100 V to some 800 μm wide zipping actuators results in an electrostatic force of 100 μN and a mirror displacement of 6 μm. Recent tests of the electric behaviour show linearity between applied tension and resulting displacement as well as a good reproducibility. We also present analysis and results obtained on silicon or polymer (BCB) membranes which have to be attached on the actuator array. A preliminary assembled component made of one actuator sealed to a 5 μm thick polymer 5 × 5 mm2 (BCB) membrane has demonstrated the feasibility of deforming such a small membrane by 3 μm, which is very promising.
The Real Time Computer RTC is a key component of the Nasmyth Adaptive Optics System, controlling the 185 actuators of the deformable mirror from a 144 Shack-Hartmann subapertures wavefront sensor at a maximum frequency of 500 Hz. It also provides additional capabilities such as real time optimization of the control loop which is the warranty for NAOS to achieve a very good Strehl Ratio in a broad magnitude range (Mv equals 8 up to 18), on-line turbulence and performance estimations and finally capability to store and process the data necessary to the off-line PSF reconstruction algorithm. This RTC is also designed to be easily upgraded as for Laser Guide Star. Moreover all softwares can be easily adapted to control a curvature sensor as well as the hardware which can be used with the two types of wave front sensors.
NAOS is the adaptive optics system to be installed at one of the Nasmyth focus of the VLT. It was designed and manufactured by a French Consortium to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 micrometer spectral range. For bright sources, NAOS will achieve a Strehl ratio of 70% under average seeing conditions. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR. All the components of NAOS have been delivered and the integration phase is in progress since the beginning of 2000. After extensive tests and performance verifications in France, the system will be shipped to Chile by the end of 2000. The first light at the VLT is foreseen in the beginning of 2001.
Adaptive Optics as a new tool for astronomical observation has proved a powerful means of investigation in high angular resolution programs. However, in spite of the complexity of the components involved (wavefront sensor, real-time computer), its use must be made as simple as possible in order to make it accessible to the largest audience of observers, and to answer the more demanding needs of modern observatories such as queue scheduling, service observing or remote observing. The Computer Aided Control developed for the Nasmyth Adaptive Optics System of the Very Large Telescope, will provide the astronomer with an extensive support, from the preparation of optimized observations to the automated operation of the instrument at the telescope either for hardware control, real time computing, or even preventive maintenance.