Kacem El Hadi

Progress with extreme adaptive optics test bench for ELT at LAM

Direct detection of exo-planets from the ground will become a reality with the advent of a new class of extreme-adaptive optics instruments that will come on-line within the next few years on 8-10 meters class telescopes. One major technical challenge in reaching the requisite high contrast at small angles is the sensing and control of wave front errors which becomes even more challenging in the case of the extremely large telescopes. Extensive computer simulations have shown the ability of such systems to deliver high Strehl ratio correction expected (within EPICS preliminary study for instance) but few experiments dedicated to ELTs have been realized so far. This paper will discuss the nature of this problem, and describe recent laboratory results from the LAM Extreme Adaptive Optics bench whose purpose is to provide validation of the numerical simulations as well as to be a testbed to develop concepts, architectures, and control algorithms for the future ELTs extreme adaptive optics systems. This test bench is optimized for ultra-high contrast applications requiring XAO with realistic telescope conditions reproduced by star and turbulence generators and including segmented primary mirror. We present here preliminary results, showing an RMS wavefront control at level smaller than 10 nm rms for static aberrations.

The ELT-MOS (MOSAIC) : Towards the construction phase

When combined with the huge collecting area of the ELT, MOSAIC will be the most effective and flexible Multi-Object Spectrograph (MOS) facility in the world, having both a high multiplex and a multi-Integral Field Unit (Multi-IFU) capability. It will be the fastest way to spectroscopically follow-up the faintest sources, probing the reionisation epoch, as well as evaluating the evolution of the dwarf mass function over most of the age of the Universe. MOSAIC will be world-leading in generating an inventory of both the dark matter (from realistic rotation curves with MOAO fed NIR IFUs) and the cool to warm-hot gas phases in z=3.5 galactic haloes (with visible wavelenth IFUs). Galactic archaeology and the first massive black holes are additional targets for which MOSAIC will also be revolutionary. MOAO and accurate sky subtraction with fibres have now been demonstrated on sky, removing all low Technical Readiness Level (TRL) items from the instrument. A prompt implementation of MOSAIC is feasible, and indeed could increase the robustness and reduce risk on the ELT, since it does not require diffraction limited adaptive optics performance. Science programmes and survey strategies are currently being investigated by the Consortium, which is also hoping to welcome a few new partners in the next two years.

Opto-mechanical designs for the HARMONI adaptive optics systems

HARMONI is a visible and near-infrared integral field spectrograph equipped with two complementary adaptive optics systems, fully integrated within the instrument. A Single Conjugate AO (SCAO) system offers high performance for a limited sky coverage and a Laser Tomographic AO (LTAO) system provides AO correction with a very high sky-coverage. While the deformable mirror performing real-time correction of the atmospheric disturbances is located within the telescope itself, the instrument contains a suite of state-of-the-art and innovative wavefront sensor systems. Laser guide star sensors (LGSS) are located at the entrance of the instrument and fed by a dichroic beam splitter, while the various natural guide star sensors for LTAO and SCAO are located close to the science focal plane. We present opto-mechanical architecture and design at PDR level for these wavefront sensor systems.

Assembly, integration, test, and verification scenarios for the ELT MOSAIC instrument

Assembly, Integration, Test and Validation (AIT/V) phases for AO instruments, in laboratory as in the telescope, represent numerous technical challenges. The Laboratoire d’Astrophysique de Marseille (LAM) is in charge of the AIT/V preparation and planning for the MOSAIC (ELT-MOS) instrument, from identification of needs, challenges, risks, to defining the optimal AIT strategy for this highly modular and serialized instrument. In this paper, we present the status of this study and describe several AIT/V scenarios as well as a planning for AIT phases in Europe and in Chile. We also show our capabilities, experience and expertise to lead the instrument MOSAIC AIT/V activities.

Fourier wavefront reconstruction with a pyramid wavefront sensor

Using Fourier methods to reconstruct the phase measured by a wavefront sensor (WFS) can significantly re- duce the number of computations required, as well as easily enable predictive reconstruction methods based on knowledge of the adaptive optics system, atmospheric turbulence and wind profile. Previous work on Fourier re- construction has focused on the Shack-Hartmann WFS. With increasing interest in the highly sensitive Pyramid WFS we present the development of Fourier reconstruction tools tailored to the Pyramid sensor. We include the development of the Fourier model, it’s use for formulating error budgets and a laboratory demonstration of Fourier reconstruction with a Pyramid WFS.

Phase A AO system design and performance for MOSAIC at the ELT

MOSAIC is a mixed-mode multiple object spectrograph planned for the ELT that uses a tiled focal plane to support a variety of observing modes. The MOSAIC AO system uses 4 LGS WFS and up to 4 NGS WFS positioned anywhere within the full 10 arcminute ELT field of view to control either the ELT M4/5 alone for GLAO operation feeding up to 200 targets in the focal plane, or M4/5 in conjunction with 10 open-loop DMs for MOAO correction. In this paper we present the overall design and performance of the MOSAIC GLAO and MOAO systems.

Coupling of WFS with a segmented DM “Test of different concepts: SH, Pyramid, Zernike phase sensor”

LAM is developing several R&D activities for E-ELT instrumentation, in particular, different WFS concepts are investigated (Pyramid, ZELDA, a Zernike phase mask sensor, Phase diversity or still NL Curvature) and an ESO-EELT M1 mirror segment (1.5 m) has been demonstrated. Segmented mirrors are not only the solution for the problem of ELTs monolithic size but also for other questions related to fabrication, optics replacement and transport. And, they are widely used today for other applications: fiber coupling, LGS beam shaping, etc. Their only problem is how to assure the cophasing of segments to take advantage of the full optimum size. In the present work, we study the sensitivity to different WFS (Sack-Hartmann, Pyramid and ZELDA) to pupil phase discontinuity using a PTT mirror from Iris AO. Various test such as segment phasing, stability, saturation, flat, or still the addressing mode are then performed and compared.

An active optics concept for the multi-object spectrograph EAGLE

The reliability of active optic for telescopes and instrumentation is now good enough to make them available for day to day use in working observatories. Future telescopes and their associated instruments will benefit from this technology to offer innovative concepts, optimal performance and improved reliability. An optical design of the multi-objects spectrograph EAGLE using, active surfaces, is detailed in this article. The first active component is a steering mirror, included in the target acquisition system, able to compensate for large astigmatism variations due to the variable off-axis design. This innovative design also includes two variable curvature mirrors authorising focus compensation and adding a zoom facility. A complete description of these active mirrors mechanical principle is presented, from elasticity theory to opto-mechanical design. The prototypes of these active mirrors with their complete test bench are detailed.

Product assurance for instrumental projects in research laboratory: galaxies, etoiles, physique, instrumentation (GEPI)

Product Assurance is an essential activity to support the design and construction of complex instruments developed for major scientific programs. The international size of current consortia in astrophysics, the ambitious and challenging developments, make the product assurance issues very important. The objective of this paper is to focus in particular on the application of Product Assurance Activities to a project such as MOSAIC, within an international consortium. The paper will also give a general overview on main product assurance tasks to be implemented during the development from the design study to the validation of the manufacturing, assembly, integration and test (MAIT) process and the delivery of the instrument.

System analysis and expected performance of a high-contrast module for HARMONI

HARMONI is a first-light visible and near-IR integral field spectrograph of ESO’s Extremely Large Telescope (ELT) which will sit on top of Cerro Armazones, Chile. A Single Conjugate Adaptive Optics (SCAO) subsystem will provide diffraction-limited spectro-images in a Nyquist-sampled 0.61 x 0.86 arcsec field of view, with a R=3000-20000 spectral resolution. Inside the instrument, a High Contrast Module (HCM) could give HARMONI the ability to spectrally characterize young giant exoplanets (and disks) with flux ratio down to 10−6 as close as 100-200mas from their star. This would be achieved with an apodized pupil coronagraph to attenuate the diffracted light of the star and limit the dynamic range on the detector, and an internal ZELDA wavefront sensor to calibrate non-common path aberrations, assuming that the surface quality of the relay optics of HARMONI satisfy specific requirements. This communication presents (a) the system analysis that was conducted to converge towards these requirement, and the proposed HCM design, (b) an end-to-end simulation tool that has been built to produce realistic datacubes of hour-long observations, and (c) the estimated performance of the HCM, which has been derived by applying differential imaging techniques on the simulated data.