This paper describes instrumentation used to adapt the Dunn Solar Telescope (DST) located on Sacramento Peak in Sunspot, NM for observations using the Doppler Spectro Imager (DSI). The DSI is based on a Mach-Zehnder interferometer and measures the Doppler shift of solar lines allowing for the study of atmospheric dynamics of giant planets and the detection of their acoustic oscillations. The instrumentation is being designed and built through a collaborative effort between a French team from the Observatoire de la Cote d’Azur (OCA) that designed the DSI and a US team at New Mexico State University (NMSU). There are four major components that couple the DSI to the DST: a guider/tracker, fast steering mirror (FSM), pupil stabilizer and transfer optics. The guider/tracker processes digital video to centroid-track the planet and outputs voltages to the DST’s heliostat controls. The FSM removes wavefront tip/tilt components primarily due to turbulence and the pupil stabilizer removes any slow pupil “wander” introduced by the telescope’s heliostat/turret arrangement. The light received at a science port of the DST is sent through the correction and stabilization components and into the DSI. The FSM and transfer optics designs are being provided by the OCA team and serve much the same functions as they do for other telescopes at which DSI observations have been conducted. The pupil stabilization and guider are new and are required to address characteristics of the DST.
The measurements of radial velocity fields on planets with a Doppler Spectro-Imager allow the study of atmospheric dynamics of giant planets and the detection of their acoustic oscillations. The frequencies of these oscillations lead to the determination of the internal structure by asteroseismology. A new imaging tachometer, based on a Mach-Zehnder interferometer, has been developed to monitor the Doppler shift of solar lines reflected at the surface of the planets. We present the principle of this instrument. A prototype was designed and built, following the specifications of a future space mission. The performance of the prototype, both at the laboratory and on the sky, is presented here.
Future extremely large telescopes will open a niche for exoplanet direct imaging at the expense of using a primary segmented mirror which is known to hamper high-contrast imaging capabilities. The focal plane diffraction pattern is dominated by bright structures and the way to reduce them is not straightforward since one has to deal with strong amplitude discontinuities in this kind of unfriendly pupil (segment gaps and secondary support). The SPEED experiment developed at Lagrange laboratory is designed to address this specific topic along with high-contrast at very small separation. The baseline design of SPEED will combine a coronagraph and two deformable mirrors to create dark zones at the focal plane. A first step in this project was to identify under which circumstances the deep contrast at small separation is achievable. In particular, the DMs location is among the critical aspect to consider and is the topic covered by this paper.
Theia is an astrometric mission proposed to ESA in 2014 for which one of the scientific objectives is detecting
Earth-like exoplanets in the habitable zone of nearby solar-type stars. This objective requires the capability
to measure stellar centroids at the precision of 1x10-5 pixel. Current state-of-the-art methods for centroid
estimation have reached a precision of about 3x10-5 pixel at two times Nyquist sampling, this was shown at
the JPL by the VESTA experiment. A metrology system was used to calibrate intra and inter pixel quantum
efficiency variations in order to correct pixelation errors. The Theia consortium is operating a testbed in vacuum
in order to achieve 1x10-5 pixel precision for the centroid estimation. The goal is to provide a proof of concept
for the precision requirement of the Theia spacecraft.
The testbed consists of two main sub-systems. The first one produces pseudo stars: a blackbody source is
fed into a large core fiber and lights-up a pinhole mask in the object plane, which is imaged by a mirror on the
CCD. The second sub-system is the metrology, it projects young fringes on the CCD. The fringes are created by
two single mode fibers facing the CCD and fixed on the mirror. In this paper we present the latest experiments
conducted and the results obtained after a series of upgrades on the testbed was completed. The calibration
system yielded the pixel positions to an accuracy estimated at 4x10-4 pixel. After including the pixel position
information, an astrometric accuracy of 6 x 10-5 pixel was obtained, for a PSF motion over more than 5 pixels.
In the static mode (small jitter motion of less than 1 x 10-3 pixel), a photon noise limited precision of 3x10-5
pixel was reached.
The SPEED project - the Segmented Pupil Experiment for Exoplanet Detection - in development at the Lagrange laboratory, aims at gearing up strategies and technologies for high-contrast instrumentation with segmented telescopes. This new instrumental platform offers an ideal environment in which to make progress in the domain of ELTs and/or space-based missions with complex apertures. It combines all the required recipes (phasing optics, wavefront control/shaping, and advanced coronagraphy) to get to very close angular separation imaging. In this paper, we report on the optical design and subsystems advances and we provide a progress overview.
NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. NEAT requires the capability to measure stellar centroids at the precision of 5 x 10-6 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 2 x 10-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment. A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors. The European part of the NEAT consortium is building a testbed in vacuum in order to achieve 5 x 10-6 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. The testbed consists of two main sub-systems. The first one produces pseudo stars: a blackbody source is fed into a large core fiber and lights-up a pinhole mask in the object plane, which is imaged by a mirror on the CCD. The second sub-system is the metrology, it projects young fringes on the CCD. The fringes are created by two single mode fibers facing the CCD and fixed on the mirror. In this paper we present the experiments conducted and the results obtained since July 2013 when we had the first light on both the metrology and pseudo stars. We explain the data reduction procedures we used.
One of the most challenging fields of astronomical instrumentation is probably high-contrast imaging since it ultimately
combines ultra-high sensitivity at low flux and the ability to cope with photon flux contrasts of several hundreds of
millions or even more. These two aspects implicitly require that high-contrast instruments should be highly stable in the
sense of the reproducibility of their measurements at different times, but also, continuously stable over time. In most
high contrast instruments or experiments, their sensitivity is broken after at most tens of minutes of operation due to
uncontrolled and unknown behaviour of the whole experiment regarding the environmental conditions. In this paper, we
introduce a general approach of an exhaustive stability study for high-contrast imaging that has been initiated at
Lagrange Laboratory, Observatoire de la Côte d'Azur (OCA). On a practical ground, one of the fundamental issues of
this study is the metrology, which is the basis of all reproducible measurements. We describe a small experiment
designed to understand the behaviour of one of our ultra-precise metrology tools (a commercial sub-nanometric 3-way
interferometer) and derive the conditions under which its operation delivers reliable results. The approach will apply to
the high-contrast imaging test-bench SPEED, under development at OCA.
Searching for nearby exoplanets with direct imaging is one of the major scientific drivers for both space and groundbased programs. While the second generation of dedicated high-contrast instruments on 8-m class telescopes is about to greatly expand the sample of directly imaged planets, exploring the planetary parameter space to hitherto-unseen regions ideally down to Terrestrial planets is a major technological challenge for the forthcoming decades. This requires increasing spatial resolution and significantly improving high contrast imaging capabilities at close angular separations. Segmented telescopes offer a practical path toward dramatically enlarging telescope diameter from the ground (ELTs), or achieving optimal diameter in space. However, translating current technological advances in the domain of highcontrast imaging for monolithic apertures to the case of segmented apertures is far from trivial. SPEED – the segmented pupil experiment for exoplanet detection – is a new instrumental facility in development at the Lagrange laboratory for enabling strategies and technologies for high-contrast instrumentation with segmented telescopes. SPEED combines wavefront control including precision segment phasing architectures, wavefront shaping using two sequential high order deformable mirrors for both phase and amplitude control, and advanced coronagraphy struggled to very close angular separations (PIAACMC). SPEED represents significant investments and technology developments towards the ELT area and future spatial missions, and will offer an ideal cocoon to pave the road of technological progress in both phasing and high-contrast domains with complex/irregular apertures. In this paper, we describe the overall design and philosophy of the SPEED bench.
NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. In NEAT, one fundamental aspect is the capability to measure stellar centroids at the precision of 5 × 10-6 pixel.
Current state-of-the-art methods for centroid estimation have reached a precision of about 2 × 10-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment.1 A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors.
The European part of the NEAT consortium is building a testbed in vacuum in order to achieve 5 × 10-6
pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. In this paper we present the metrology and the pseudo stellar sources sub-systems, we present a performance model and an error budget of the experiment and finally we describe the present status of the demonstration.
The purpose of this paper is to give an overview of the state of the art wavefront sensor detectors developments held in
Europe for the last decade.
The success of the next generation of instruments for 8 to 40-m class telescopes will depend on the ability of Adaptive
Optics (AO) systems to provide excellent image quality and stability. This will be achieved by increasing the sampling,
wavelength range and correction quality of the wave front error in both spatial and time domains.
The modern generation of AO wavefront sensor detectors development started in the late nineties with the CCD50
detector fabricated by e2v technologies under ESO contract for the ESO NACO AO system. With a 128x128 pixels
format, this 8 outputs CCD offered a 500 Hz frame rate with a readout noise of 7e-.
A major breakthrough has been achieved with the recent development by e2v technologies of the CCD220. This
240x240 pixels 8 outputs EMCCD (CCD with internal multiplication) has been jointly funded by ESO and Europe under
the FP6 programme. The CCD220 and the OCAM2 camera that operates the detector are now the most sensitive system
in the world for advanced adaptive optics systems, offering less than 0.2 e readout noise at a frame rate of 1500 Hz with
negligible dark current. Extremely easy to operate, OCAM2 only needs a 24 V power supply and a modest water cooling circuit. This system, commercialized by First Light Imaging, is extensively described in this paper. An upgrade of
OCAM2 is foreseen to boost its frame rate to 2 kHz, opening the window of XAO wavefront sensing for the ELT using 4
synchronized cameras and pyramid wavefront sensing.
Since this major success, new developments started in Europe. One is fully dedicated to Natural and Laser Guide Star
AO for the E-ELT with ESO involvement. The spot elongation from a LGS Shack Hartman wavefront sensor
necessitates an increase of the pixel format. Two detectors are currently developed by e2v. The NGSD will be a 880x840
pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate. The LGSD is a scaling of the NGSD
with 1760x1680 pixels and 3 e readout noise (goal 1e) at 700 Hz (goal 1000 Hz) frame rate. New technologies will be
developed for that purpose: advanced CMOS pixel architecture, CMOS back thinned and back illuminated device for
very high QE, full digital outputs with signal digital conversion on chip. In addition, the CMOS technology is extremely
robust in a telescope environment. Both detectors will be used on the European ELT but also interest potentially all giant
telescopes under development.
Additional developments also started for wavefront sensing in the infrared based on a new technological breakthrough
using ultra low noise Avalanche Photodiode (APD) arrays within the RAPID project. Developed by the SOFRADIR and
CEA/LETI manufacturers, the latter will offer a 320x240 8 outputs 30 microns IR array, sensitive from 0.4 to 3.2
microns, with 2 e readout noise at 1500 Hz frame rate. The high QE response is almost flat over this wavelength range.
Advanced packaging with miniature cryostat using liquid nitrogen free pulse tube cryocoolers is currently developed for
this programme in order to allow use on this detector in any type of environment. First results of this project are detailed
These programs are held with several partners, among them are the French astronomical laboratories (LAM, OHP,
IPAG), the detector manufacturers (e2v technologies, Sofradir, CEA/LETI) and other partners (ESO, ONERA, IAC,
GTC). Funding is: Opticon FP6 and FP7 from European Commission, ESO, CNRS and Université de Provence,
Sofradir, ONERA, CEA/LETI and the French FUI (DGCIS).
Detection of exoplanets implies the measure of extremely weak signals, usually below intensity perturbations in the PSF caused by static aberrations. We have finished the construction of a new test bench called FFREE - Fresnel Free
Experiment for EPICS. The scope of the FFREE experiment is the active speckles correction using off-line cancellation
techniques: Electric Field Conjugation and Phase Diversity, in view of a future instrument EPICS for the telescope EELT
(ESO). We will describe the system and discuss some characteristics like the chromatism and the environmental
stability of the bench.
NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like
exoplanets in the habitable zone of nearby solar-type stars. In NEAT, one fundamental aspect is the capability to
measure stellar centroids at the precision of 5 x 10-6 pixel.
Current state-of-the-art methods for centroid estimation have reached a precision of about 4 x 10-5 pixel at Nyquist sampling. Simulations showed that a precision of 2 μ-pixels can be
reached, if intra and inter pixel quantum efficiency variations are calibrated and corrected for
by a metrology system.
The European part of the NEAT consortium is designing and building a testbed in vacuum in order to
5 x 10-6 pixel precision for the centroid estimation. The goal is to provide a proof of
concept for the precision
requirement of the NEAT spacecraft. In this paper we give the basic relations and trade-offs
that come into play for the design of a centroid testbed and its metrology system. We detail the
different conditions necessary to reach the targeted precision, present the characteristics of
our current design and describe the present status of the demonstration.
ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets
direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas
giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The
segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the
detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the
overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and
post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the
concepts for common path and diffraction suppression system is presented. The performance of the instrument is
predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through
the various optical elements.
The purpose of FFREE - the new optical bench devoted to experiments on high-contrast imaging at LAOG - consists in
the validation of algorithms based on off-line calibration techniques and adaptive optics (AO) respectively for the
wavefront measurement and its compensation. The aim is the rejection of the static speckles pattern arising in a focal
plane after a diffraction suppression system (based on apodization or coronagraphy) by wavefront pre-compensation. To
this aim, FFREE has been optimized to minimize Fresnel propagation over a large near infrared (NIR) bandwidth in a
way allowing efficient rejection up to the AO control radius, it stands then as a demonstrator for the future
implementation of the optics that will be common to the scientific instrumentation installed on EPICS.
Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and
explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based
telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the discovery space
towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. EPICS is a
proposed instrument for the European ELT, dedicated to the detection and characterization of Exoplanets by direct
imaging, spectroscopy and polarimetry. ESO completed a phase-A study for EPICS with a large European consortium
which - by simulations and demonstration experiments - investigated state-of-the-art diffraction and speckle suppression
techniques to deliver highest contrasts. The paper presents the instrument concept and analysis as well as its main
innovations and science capabilities. EPICS is capable of discovering hundreds of giant planets, and dozens of lower
mass planets down to the rocky planets domain.
This paper describes the principle function and the possible applications of a new micropositioning device for the optical fiber, which aligns it precisely to a light source, with a resolution better than 100 nm. One end of an optical fiber is fixed to one end of a piezoelectric tube. The electrical voltage applied to the 5 external electrodes around the piezoelectric tube will create transverse motion (up till +/- 20 μm) and longitudinal motion (of 1 to 2 μm) and the optical fiber fixed to this tube will make the same motion. The other end of the optical fiber passing through the tube fixed to a support is connected to a photometer, which measures the light intensity. The measure allows determining the best voltage for the command of the 5 electrodes with a help of programmed algorithms. Small dimension and very short time response of this device would allow multiple applications for the light injection in a wave-guide. The first application is related to the guide to guide light coupling, for the automatic centering of two optical fibers, and a fiber to the input of an integrated optics beam combiner. The second application concerns pupil's fragmentation and second generation VLTI instruments. The alignment of height optical fibers with an object of the sky, coming from height telescopes or height sub-pupils of one telescope, could be controlled independently and in real time. The light coupling into every fiber and the optical length path are micro-adjusted in an optimal way, in spite of atmospheric turbulence effects.
WIRCam (Wide-field InfraRed Camera) is a near-infrared (0.9-2.4 microns) camera developed for the prime focus of the Canada France Hawaii Telescope (CFHT), a 3.6-m telescope located on Mauna Kea, Hawaii. WIRCam is based on 4 x 2048x2048 HAWAII2RG arrays, developed by Rockwell. The camera provides a 0.3"/pixel sampling, and the close packaging of the detectors allows to cover an almost contiguous field-of-view of 20.5' x 20.5'. All optical elements are assembled in a cryovessel and cooled down to 85K by a He closed cycle cryogenerator. The two filter wheels have capacity for 8 filters (110 mm in diameter), cooled at low temperature together with the Lyot stop. These wheels are mounted on sapphire ball bearings and powered by external motors. Passive spring indexers define their positioning. A fused-silica tip/tilt plate powered by voice coil type motors provides image stabilization in front of the cryovessel. It compensates for flexures as well as for low frequency telescope oscillations from wind shake. This paper describes the overall architecture of the camera, giving the optical estimated performances and details some specific points of the design such as filter wheels, thermal connections, etc.