EAGLE is the multi-object spatially-resolved near-IR spectrograph instrument concept for the E-ELT, relying
on a distributed Adaptive Optics, so-called Multi Object Adaptive Optics. This paper presents the results of
a phase A study. Using 84×84 actuator deformable mirrors, the performed analysis demonstrates that 6 laser
guide stars (on an outer ring of 7.2' diameter) and up to 5 natural guide stars of magnitude R < 17, picked-up in
a 7.3' diameter patrol field of view, allow us to obtain an overall performance in terms of Ensquared Energy of
35% in a 75×75<i>mas</i><sup>2</sup> resolution element at H band whatever the target direction in the centred 5' science field
for median seeing conditions. In terms of sky coverage, the probability to find the 5 natural guide stars is close
to 90% at galactic latitudes |b| ~ 60 deg. Several MOAO demonstration activities are also on-going.
Tomographic AO (or Wide Field AO) systems use LGS to build a 3D model of turbulence, but rely on NGS for
low order sensing. .To preserve reasonable sky coverage, each photon coming from the NGS to sense Tip Tilt has
to be optimally exploited. That means a smart control law, a low detection noise, a concentration of the photons
onto a small patch and a wave front sensor concept with favorable noise propagation. In this paper, we describe
the system choices that were made during the E-ELT laser tomographic system ATLAS phase A study, in order
to get a sky coverage as close as possible to 100%. A correct estimation of the sky coverage is therefore a key
issue. We have developped a sky coverage estimation strategy based on a Besan¸con model starfield generation,
a star(s) selection tool, and a careful estimation of the residual anisoplanatism (after reconstruction process
between the NGSs), noise and temporal contributors. We describe the details of the procedure, and derive the
ATLAS expected performance.
In the framework of exoplanet direct imaging, a few coronagraphs have been proposed to overcome the large flux ratio
that exists between the star and its planet. However, there are very few solutions that gather in the same time broad band
achromaticity, a small inner working angle (shortest angular distance for planet detection), a good throughput for the
planet light, and a mature technical feasibility. Here, we propose to use a combination of chromatic Four Quadrant Phase
Mask coronagraphs to achromatize the dephasing of this well-studied monochromatic coronagraph. After describing the
principle of the technique, we present preliminary results for a compact prototype. Contrast larger than 10000 are
reached with more than 250 nm of spectral bandwidth in the visible. Stability over time and effect of the filtering is also
EAGLE is an instrument for the European Extremely Large Telescope (E-ELT). EAGLE will be installed at the Gravity
Invariant Focal Station of the E-ELT, covering a field of view of 50 square arcminutes. Its main scientific drivers are the
physics and evolution of high-redshift galaxies, the detection and characterization of first-light objects and the physics of
galaxy evolution from stellar archaeology. These key science programs, generic to all ELT projects and highly
complementary to JWST, require 3D spectroscopy on a limited (~20) number of targets, full near IR coverage up to 2.4
micron and an image quality significantly sharper than the atmospheric seeing. The EAGLE design achieves these
requirements with innovative, yet simple, solutions and technologies already available or under the final stages of
development. EAGLE relies on Multi-Object Adaptive Optics (MOAO) which is being demonstrated in the laboratory
and on sky. This paper provides a summary of the phase A study instrument design.
EAGLE is a wide FoV (5 arcmin diameter), multi-objects (at least 20) integral-field spectrograph (R>4000) for the E-ELT.
The top level requirements are to concentrate 30 to 40 % of the photons collected by the E-ELT in a focal area of
75x75 mas<sup>2</sup> in H band. This leads to the selection of the Multi Object Adaptive Optics in order to deliver such a
performance in a so-large FoV. In this paper, we present a detailed analysis of the error budget for an MOAO system in
EAGLE. It is based on numerical simulation results. The budget is splitted in LGS and NGS contributions. The analysis
leads to share the specifications between low spatial frequencies and high spatial frequencies in the wave-front errors.
Finally a preliminary conceptual design of the MOAO system is deduced including 9 LGS for tomography and a 9000
actuator deformable mirror per channel.
In this paper we focus on wide Field of View (FoV) Adaptive Optics (AO) correction for the EAGLE instrument for the
European Extremely Large Telescope (E-ELT). The main goal is to increase the Ensquared Energy (EE) so as to reach
decent spectroscopic SNRs as well as achieving a good spatial resolution. This typically means that more than 40% of
the PSF flux has to be gathered into a 75x75 mas<sup>2</sup> box. Moreover, for such an application, the correction does not have to
be uniform over the whole 5 arcmin FoV but just has to be optimised in a few directions, i.e. the scientific targets. In that
frame we study the performance of Multi-Object AO (MOAO) systems, where we focus on the influence of the Guide
Star constellations and the consequences of using Laser Guide Stars (LGS) for wavefront sensing. Unfortunately, for
such sources, low-order modes such as tip/tilt modes cannot be measured. We have therefore developed a new method
allowing us to partially simulate such effects in analytical AO simulation codes, which is highly detailed in this paper.
Thanks to this method, we have been able to derive preliminary results in terms of system design as well as sky
EAGLE is an instrument under conceptual study for the European Extremely Large Telescope (E-ELT). EAGLE will be
installed at the Gravity Invariant Focal Station of the E-ELT, covering a field of view between 5 and 10 arcminutes. Its
main scientific drivers are the physics and evolution of high-redshift galaxies, the detection and characterization of first-light
objects and the physics of galaxy evolution from stellar archaeology. The top level requirements of the instrument
call for 20 spectroscopic channels in the near infrared, assisted by Adaptive Optics. Several concepts of the Target
Acquisition sub-system have been studied and are briefly presented. Multi-Conjugate Adaptive Optics (MCAO) over a
segmented 5' field has been evaluated and compared to Multi-Object Adaptive Optics (MOAO). The latter has higher
performance and is easier to implement, and is therefore chosen as the baseline for EAGLE. The paper provides a status
report of the conceptual study, and indicates how the future steps will address the instrument development plan due to be
completed within a year.
One of the highlights of the European ELT Science Case book is the study of resolved stellar populations, potentially out to the Virgo Cluster of galaxies. A European ELT would enable such studies in a wide range of unexplored, distant environments, in terms of both galaxy morphology and metallicity. As part of a small study, a revised science case has been used to shape the conceptual design of a multi-object, multi-field spectrometer and imager (MOMSI). Here we present an overview of some key science drivers, and how to achieve these with elements such as multiplex, AO-correction, pick-off technology and spectral resolution.
Numerical Simulation is an essential part of the design and optimisation of astronomical adaptive optics systems. Simulations of adaptive optics are computationally expensive and the problem scales rapidly with telescope aperture size, as the required spatial order of the correcting system increases. Practical realistic simulations of AO systems for extremely large telescopes are beyond the capabilities of all but the largest of modern parallel supercomputers. Here we describe a more cost effective approach through the use of hardware acceleration using field programmable gate arrays. By transferring key parts of the simulation into programmable logic, large increases in computational bandwidth can be expected. We show that the calculation of wavefront sensor images (involving a 2D FFT, photon shot noise addition, background and readout noise), and centroid calculation can be accelerated by factor of 400 times when the algorithms are transferred into hardware. We also provide details about the simulation platform and framework that we have developed at Durham.
FALCON is an original concept for a next generation instrument which could be used on the ESO Very Large Telescope (VLT) and on the future Extremely Large Telescopes (ELT). It is a multi-objects integral field spectrograph with multiple small integral field units (IFUs). Each of them integrates a tiny adaptive optics system coupled with atmospheric tomography to solve the sky coverage problem. This therefore allows to reach spatial (0.15 - 0.25 arcsec) and spectral (R>=5000) resolutions suitable for distant galaxy studies in the 0.8-1.8 μm wavelength range. In the FALCON concept, the adaptive optics correction is only applied on small and discrete areas selected within a large field. This approach implies to develop miniaturized devices for wavefront correction such as deformable mirrors (DM) and wavefront sensors (WFS). We draw up here the main high level specifications for this instrument, that we derive in a first set of opto-mechanical DM requirements including the state of the art of DM technologies.
Since the pioneering work of Haniff et al. (1987), aperture-masking interferometry has been demonstrated on large class telescopes. The usual implementation lays in the avoidance of redundancies in the pupil plane, which, in presence of aberrations and turbulence, depress the transfer function of the telescope. In a recent experiment on Keck I, a non-redundant pupil geometry allowed diffraction-limited imaging, with dynamic range in excess of 200:1 (Tuthill et al., 2000). Yet, the final image quality is still limited by the optical defects induced by turbulence in sub-pupils. We propose to overcome this issue by using the same technique of spatial filtering by single-mode fibers that we have used in long-baseline interferometry. Each sub-pupil element is focused in a single-mode fiber thus eliminating spatial phase fluctuations and trading these against instantaneous intensity fluctuations which can be directly measured. Therefore, each sub-pupil becomes spatially coherent. Simulations show that the dynamic range would be dramatically increased. Moreover, the idea of using fibers in the pupil plane could lead to outstanding prospects, like filtering the whole aperture, sub-divided into a filled array of sub-apertures.
FALCON is an original concept for a next generation spectrograph at ESO VLT or at future ELTs. It is a spectrograph including multiple small integral field units (IFUs) which can be deployed within a large field of view such as that of VLT/GIRAFFE. In FALCON, each IFU features an adaptive optics correction using off-axis natural reference stars in order to combine, in the 0.8 - 1.8 μm wavelength range, spatial and spectral resolutions (0.1 - 0.15 arcsec and R = 1000 +/- 5000). These conditions are ideally suited for distant galaxy studies, which should be done within fields of view larger than the galaxy clustering scales (4 - 9 Mpc), i.e. foV > 100 arcmin. Instead of compensating the whole field, the adaptive correction will be performed locally on each IFU. This implies to use small miniaturized devices both for adaptive optics correction and wavefront sensing. Applications to high latitude fields imply to use atmospheric tomography because the stars required for wavefront sensing will be in most of the cases far outside the isoplanatic patch.
We present FALCON, a concept of new generation multi-objects integral field spectrograph with adaptive optics for the ESO VLT. The goal of FALCON is to combine high angular resolution (0.15 - 0.25 arcsec) and high spectral resolution (R≥5000) in the 0.8-1.8 μm wavelength range across the Nasmyth field (25 arcmin). Instead of compensating the whole field, the correction will be performed locally on each scientific object. This implies to use small miniaturized devices for adaptive optics correction and wavefront sensing. The main scientific objective of FALCON will be extragalactic astronomy. It will therefore have to use atmospheric tomography because the stars required for wavefront sensing will be in most of the cases far outside the isoplanatic patch. We show in this paper that applying adaptive optics correction will provide an important increase in signal to noise ratio, especially for distant galaxies at high redshift.
We present, in this article, an analytical study of the phase reconstruction error for MCAO systems. Two approaches are considered; a classical estimator based on a Least Square (LS) approach and a Maximum A Posteriori (MAP) estimator which uses the prior knowledge we have both on the measurement noise and the turbulence volume statistics. The effects of these modes both on the phase reconstruction and on the phase correction error are studied and quantified. T is shown that, using a MAP approach, a large part of the unseen modes can be extrapolated using correlations between unseen eigenmode coefficients and well-measured coefficients. We observe that the use of a MAP estimator allows a significant gain in terms of correction quality in the whole field of view.