AO4ELT 2

Optical Tube Assemblies for the ESO VLT Four Laser Guide Star Facility

Niek DOELMAN — 2011-09-08T13:39:28Z

Submitted by Fred Kamphues

Authors

R. Henselmans, D. Nijkerk, M. Lemmen, N.Rijnveld, N. Doelman, F.Kamphues

Affiliations

TNO

Abstract

ESO is implementing a new Adaptive Optics facility (AOF) on the Unit Telescope 4 (UT4) of the Very Large Telescope (VLT). For increased sky coverage, Four Laser Guide Star Facilities (4LGSF) will be installed. TNO is developing the Optical Tube Asssemblies (OTAs) for the 4LGSF.The OTAs are Galilean 20x beam expanders, expanding a ∅15 mm input beam to a steerable ∅300 mm output beam with a wavefront quality requirement of <50 nm rms. The allowed defocus under the influence of the changing environmental air temperature (0-15°C, -0.7°C/hr gradient) is only 0.2 waves. The thermal behaviour of the system has been analyzed by combining optical, lumped mass and FE analyses. The design is passively athermalized over a large temperature range as well as under the influence of thermal gradients. Extensive thermal and high power laser testing has shown the system performs as required. This poster describes the design and test results.

Predicted sky coverage for the TMT MCAO system NFIRAOS

David ANDERSEN — 2011-07-11T22:12:11Z

Authors

David Andersen, Lianqi Wang, Brent Ellerbroek, Glen Herriot

Affiliations

NRC HIA, TMT

Abstract

TMT has chosen the MCAO system NFIRAOS to be its first light AO system in part to provide astronomers with exceptional sky coverage. The TMT science requirements demand that its AO system provide wavefront errors of less than or equal to 191 nm at the galactic pole at least 50% of the time (under median atmospheric conditions when observing at zenith). This requirement drove many aspects of the NFIRAOS design from the size of the FOV, to the use of NIR MCAO-corrected NGSs, to the sensitivity of the WFSs (and corresponding limiting magnitude of the NGSs). In this paper, we build upon the sky coverage simulations of L. Wang et al. to produce smooth sky coverage maps generated for different hour angles (potential exposure time lengths), and different atmospheric conditions. We show that NFIRAOS should meet its sky coverage requirement at the North Galactic Pole, and that the sky coverage generally will be much higher than 50% at lower galactic latitudes.

Design of the calibration unit for the MOAO demonstrator Raven

Jean-françois LAVIGNE — 2011-07-11T22:10:34Z

Authors

Jean-François Lavigne, Frédéric Lamontagne, Min Wang, Marc-André Boucher

Affiliations

Institut national d'optique

Abstract

The UVic AO Lab in collaboration with HIA and the Subaru telescope is currently designing Raven, a multi-object adaptive optics (MOAO) demonstrator that will be coupled to the Subaru Infrared Camera and Spectrograph (IRCS). Its main goal will be to demonstrate MOAO feasibility on the sky while allowing astronomers to beneficiate from the increased observing efficiency associated with such systems.

Raven will use three natural guide stars (NGS) or two natural guide stars and Subaru laser guide star (LGS) to do the tomographic reconstruction of the atmosphere turbulence. The appropriate correction will then be applied to two science fields that will feed IRCS. The wavelengths between 0.6 and 0.9 µm will be used for the wavefront sensing while the science wavelengths between 0.9 and 2.5 µm will be directed towards IRCS.

INO is currently designing the Raven calibration unit. This sub-system consists in a telescope simulator that will allow aligning Raven components during its integration, testing its AO performances in the laboratory or at the telescope and calibrating the AO system by building the interaction matrix and measuring the non-common path aberrations (NCPA).

The calibration unit will provide a 9x9 grid of broadband (0.6 to 2.5 µm) NGS sources diffraction limited above 1.0 µm and located in a 2.7' circular FoV. It will allow to vary the NGS sources intensity to emulate stars ranging from R=8 to R=16. An on-axis LGS that can be conjugated to altitudes varying from 85 km to 180 km and intensity ranging from R=5 to R=11 will also be simulated. An on-axis bright white source conjugated to infinity will be installed for the user to see the beam during alignment. The calibration unit will include two deployable phase screens conjugated at altitudes of 5 km and 11 km and a deformable mirror conjugated to the ground.

Slicer based integral-field spectroscopy at the diffraction limit

Matthias TECZA — 2011-05-17T13:42:46Z

submitted by M. Tecza

Authors

M. Tecza

Affiliations

University of Oxford

Abstract

Integral-field spectroscopy (IFS) measures the spectra of all field points in a two-dimensional field-of-view simultaneously and hence makes very efficient use of telescope time. Over the last 20 years it has evolved from a niche instrumental technique in to a mainstream astronomical tool. IFS has a wide range of astronomical applications from solar system science, high contrast imaging of exoplanets to studying the properties of galaxies at any redshift out to first light. This versatility has led to almost all ground-based telescopes, as well as some space-borne observatories, having IFS capability and IFS' are the natural choice for first light instruments on future extremely large telescopes. Only few IFSs are fed by adaptive optics and can take advantage of diffraction limited performance. I describe current and forthcoming instruments that will make use of the diffraction limit, in particular I focus on IFS in operation on-sky that are slicer-based, a technology that has been thought to limit the image quality at the diffraction limit because of differential aberrations between slices originating in the spectrograph. I will describe the SINFONI and SWIFT instruments that have demonstrated that slicer-based IFS not only deliver very good image quality at the diffraction limit, but that they also have the advantages of a more efficient use of detector real estate while providing a larger simultaneous wavelength coverage compared to lenslet based IFS. As such they are the ideal instruments to exploit the high angular resolution and high sensitivity of future ELTs.

Experimental validation of LGS wavefront sensing in presence of low-order modes induced by Sodium profile variations

Laura SCHREIBER — 2011-05-16T20:00:30Z

submitted by L. Schreiber

Authors

Laura Schreiber (1)(2) Matteo Lombini (3) Emiliano Diolaiti (3) Giovanni Bregoli (3) Giuseppe Cosentino (1) Italo Foppiani (3)

Affiliations

(1) Università di Bologna – Dipartimento di Astronomia (2) INAF – Osservatorio Astronomico di Padova (3) INAF – Osservatorio Astronomico di Bologna

Abstract

The current baseline for the Multi-Conjugate adaptive optics module (MAORY) for the E-ELT is based on 6 Sodium Laser Guide Stars (LGS) projected from the edge of the telescope pupil. LGS wavefront sensing is performed by 6 Shack-Hartmann WFS of order 84x84 operated at 500Hz. The slope measurement accuracy is affected by the perspective elongation effect: the loss of performance may be mitigated through advanced centroiding algorithms, that however require a ‘template' of the LGS spot in each subaperture. While the template is being used, some sodium profile variation unavoidably occurs. This mismatch between the template and the actual spot translates into time varying low order aberrations that must be monitored by a Reference Wavefront Sensor (WFS) based on Natural Guide Stars. The dimensioning of this WFS in term of number of required subapertures and operating frequency is a key aspect with potentially strong impact on the final sky coverage of MAORY. The LGS WFS laboratory prototype available at INAF – Osservatorio Astronomico di Bologna has been enhanced in order to simulate automatically variable and repeatable sodium profiles and ‘quantify' the order and power of non-atmospherical aberrations induced by the sodium variation itself and by its effect on advanced centroid algorithms. This paper shows the results of the tests performed with this improved prototype.

The SCAO module of the E-ELT adaptive optics imaging camera MICADO

Yann CLENET — 2011-05-16T20:00:25Z

Submitted by Y. Clénet

Authors

Clénet (1), Y.; Bernardi, P. (1); Chapron, F. (1); Gendron, E. (1); Rousset, G. (1); Hubert, Z. (1); Davies, R. (2); Thiel, M. (2); Tromp, N. (3)

Affiliations

(1) LESIA ; (2) MPE ; (3) ASTRON

Abstract

MICADO is the wide-field imaging camera selected for first-light of the E-ELT. It should be coupled to the MCAO module MAORY. In addition to this wide-field correction, the MICADO team has worked on a SCAO system to provide on-axis AO correction during the first years of MICADO operation.

We will present the results of the study of this SCAO system, from the opto-mechanical point of view as well as from the AO performance point of view

DRAGON, a flexible, visible-light AO testbed

Stephen Rolt — 2011-05-16T20:00:20Z

Submitted by N. Bharmal

Authors

Stephen Rolt, Alastair Basden, Nazim Bharmal, Nigel Dipper, Deli Geng, Tim Morris, Richard Myers

Affiliations

Durham university

Abstract

DRAGON is a Durham University adaptive optics testbed, designed to accurately simulate the effects of the atmosphere for the purposes of developing high-order adaptive optics, targeted towards visible AO correction. The design consists of altitude-adjustable phase screens, a realistic sodium guide-star emulator and a set of fixed targets that can also be used as natural guide stars. The design has been optimised for both wide-field (2.5' FoV, hence MCAO/MOAO) and on-axis (SCAO) situations with 4-8m class telescopes. Since it is targeted toward visible AO, high order wavefront sensing and correction are obvious steps towards ELT-scale AO development and a key aspect of DRAGON is the integration of the Durham RTC system (see Basden, these proceedings). The design of DRAGON is discussed and its extensions towards simulating ELT-scale AO in its current configuration is explained, together with a future design explicitly scaled for ELT-scale pupils.

High-order AO in the visible, a particular niche for 4m-class telescopes?

Richard MYERS — 2011-05-16T20:00:17Z

Submitted by N. Bharmal

Authors

Richard Myers, Alastair Basden, Nazim Bharmal, Nigel Dipper, Tim Morris

Affiliations

Durham University

Abstract

The analysis of the Durham High-Order Demonstrator (DHOD) design is presented, to explore the possibility of XAO on small/4m telescopes. It does not offer the same scientific goals as XAO being deployed on 8m telescopes, such as exoplanet detection. Instead it is designed to offer itself as an on-sky technical test-bed for developing high-order AO in itself with associated control system development, together with the ability to test arbritrary coronographic technologies for enhancing imaging contrast. By designing a flexible test-bed based on the experience of the Durham group, DHOD offers a particular opportunity for instrument development that encompasses both high-order AO and high-contrast imaging. A particular design feature is the Complex Amplitude Sensor, which is designed to measure non-common path errors in order to characterise the AO-corrected PSF. The design is explained in detail and expected limiting performance estimates are displayed along with investigations of PSF characterisation taking into account realistic telescope errors such as misalignments and vibrations.

The HIA MCAO laboratory bench

Jean-Pierre VERAN — 2011-05-16T20:00:12Z

Submitted by J-P Véran

Authors

Jean-Pierre Véran (1), Dave Andersen (1), Carlos Correia (1), Glen Herriot (1), Jeff Goodwill (1), John Pazder (1), Olivier Lardière (2)

Affiliations

(1) Herzberg Institute of Astrophysics, National Research Council, Victoria, BC, Canada (2) University of Victoria, Victoria BC, Canada

Abstract

In this paper, we present our current design of an MCAO laboratory bench to support the development of NFIRAOS, the first light MCAO facility for the TMT. This MCAO bench will build on the experience of the existing LGS WFS bench at University of Victoria, which uses a focus ramp induced by a deformable mirror (DM) and source modulation during WFS integration to produce Shack-Hartmann spots with the proper radial profile. The bench will implement a closed-loop MCAO system, with two magnetic DMs, four LGS Shack-Hartmann WFSs, two NGS T/T WFS, one NGS T/T/F WFS and one higher order Truth WFS, making up a scaled down version of NFIRAOS. Turbulence on the bench will be induced by the DMs and by two additional synthetic turbulence plates. The bench will be driven by software in Matlab, at a minimum frame-rate of 1Hz, up to 15Hz.

The goals of this bench are to anchor the NFIRAOS end-to-end simulation tools; to exercise real-time LGS tomographic AO in a variety of well controlled conditions, such as faint and poorly corrected NGSs, non-uniformities in the sodium layer and field dependant Non-Common-Path Aberrations (NCPAs); develop and demonstrate calibration procedures, such PSF reconstruction and tomographic reconstruction and correction of field dependant NCPAs; and to validate optimization methods that operates at 10+ second time scales, which is not tractable in a numerical simulation, such as matched filter update and Cn2 estimation using a SLODAR method.

The Subaru Coronagraphic Extreme AO project: an XAO4ELT precursor

Frantz MARTINACHE — 2009-02-28T23:00:00Z

Submitted by Frantz MARTINACHE

Authors

F. Martinache

Affiliations

Subaru telescope

Abstract

A diffraction-limited 30-meter telescope theoretically provides a 10 mas resolution limit in the near infrared. Modern coronagraphs like the Vortex, the 8OPM and the PIAA offer the means to take full advantage of this angular resolution allowing to explore at high contrast, the innermost parts of nearby planetary systems to within a fraction of an astronomical unit: an unprecedented capability that will revolutionize our understanding of planet formation across the habitable zone. A precursor of such a system is the Subaru Coronagraphic Extreme AO project. SCExAO combines a high performance PIAA-based coronagraph downstream Subaru's AO188 AO system and a 1024-actuator MEMS DM. SCExAO employs advanced wavefront control schemes that make high contrast detection possible at 1 λ/D, providing for a few cases, the possibility to detect the light reflected by exoplanets. Moderate-high contrast detection in the super-resolution regime (<λ/D) is also possible using well calibrated closure quantities like closure-phase for a non-redundant (masked) aperture and its extension for to arbitrary apertures (Kernel-phase). Lessons learned from SCExAO's incremental deployment plan during its first 2011 engineering campaign provides insights that will guide future development of high contrast instrumentation on an ELT.