AO4ELT 2

Vibration control of ELTs

Jörg-Uwe POTT — 2011-09-16T19:00:20Z

Submitted by Jörg-uwe POTT

Authors

J.-U. Pott and the LINC-NIRVANA team

Affiliations

Max-Planck-Institute of Astronomy (MPIA), Heidelberg, Germany

Abstract

MPIA is the PI institute of the MCAO-supported Fizeau imager LINC-NIRVANA at the LBT, and a partner of the E-ELT first light NIR imager MICADO (both SCAO and MCAO assisted). LINC-NIRVANA is a true pathfinder for future ELT-AO imagers both in terms of size and technology. I will present our vibration control strategies, involving accelerometer based real-time vibration measurements, feedforward and feedback optical path control, predictive filtering, vibration sensitive active control of actuators, and the development of a dynamical model of the entire telescope. Our experiences, made with LINC-NIRVANA, will be fed into the MICADO structural AO design to reach highest on-sky sensitivity.

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.

Analysis of Ground Layer Turbulence Profiles at CTIO and Mauna Kea

Ronald GAGNE — 2011-08-19T10:09:58Z

Submitted by R. Gagné

Authors

Ronald Gagné, Paul Hickson, Thomas Pfrommer, Masen Lamb, Marc Baril

Affiliations

University of British Columbia

Abstract

For the past 4 years high-resolution ground layer turbulence measurements have been carried out on Cerro Tololo Inter-American Observatory (CTIO) with a lunar scintillometer. We present C_N2-profiles in the range up to 1 km and seeing statistics from fall 2007 to spring 2011. Comparisons with weather parameter links local topography to optical turbulence. The observations in Chile are compared to a ground-layer study on Mauna Kea at the Canada France Hawaii Telescope by the use of median seeing values as well as scale heights derived from the turbulence integral.

DAYTIME OBSERVATIONS WITH ELTs IN THE THERMAL INFRARED USING LASER GUIDE STAR ADAPTIVE OPTICS

Jacques BECKERS — 2011-08-19T10:06:24Z

Submitted by J. M. Beckers

Authors

J. M. Beckers

Affiliations

retired

Abstract

Using Magneto-Optical Filters (MOFs; also called FADOFs = Faraday Anomalous Dispersion Optical Filters) it is possible to clearly see Sodium Laser Guide Stars in the daytime sky. This makes it possible to use ELT Adaptive Optics systems for diffraction limited observations 24 hours/day. Because of the bright daytime sky this LGS AO application is only of astronomical interest in the mid-infrared wavelength region (4 – 25 microns wavelengths) where the thermal radiation of the atmosphere-telescope system dominates the scattering of sunlight thus making the day- and night- sky background comparable. Incorporating MOFs in the LGS wavefront sensor thus would more than double the ELT observing time for mid-infrared astronomy and would make sources in almost the entire sky available for observation at any time of the year. Even though the AO would increase the brightness of point-sources, it would not compete with the James Webb Space Telescope in terms of detectability. The gain with respect to the JWST lies in the 5 to 6 times better linear angular resolution. The contrast gain in brightness at near-IR wavelengths is sufficient to give sufficient natural guide stars there for tip-tilt control. MOFs have been shown to function with Na lasers in LIDAR applications (see Beckers and Cacciani, Experimental Astronomy 11, 133, 2001). The main complication associated with incorporating MOFs in ELT AO system is likely the requirement to make the telescope and its enclosure robust in the daytime environment. I refer to SPIE Proceedings 6986 (2008) for a recent reference on this topic.

Quasi-real-time end-to-end simulations of ELT-scale adaptive optics systems on GPUs

Damien GRATADOUR — 2011-08-19T10:05:40Z

Submitted by D. Gratadour

Authors

Damien Gratadour

Affiliations

LESIA

Abstract

Our team has started the development of a code dedicated to GPUs for the simulation of AO systems at the E-ELT scale. It uses the CUDA toolkit and an original binding to Yorick (an open source interpreted language) to provide the user with a comprehensive interface.

In this paper we present the first performance analysis of our simulation code, showing its ability to provide Shack-Hartmann (SH) images and measurements at the kHz scale for VLT-sized AO system and in quasi-real-time (up to 70 Hz) for ELT-sized systems on a single top-end GPU. The simulation code includes multiple layers atmospheric turbulence generation, ray tracing through these layers, image formation at the focal plane of every sub-apertures of a SH sensor using either natural or laser guide stars and centroiding on these images using various algorithms. Turbulence is generated on-the-fly giving the ability to simulate hours of observations without the need of loading extremely large phase screens in the global memory. Because of its performance this code additionally provides the unique ability to test real-time controllers for future AO systems under nominal conditions.

Phase-Sorting Interferometry for High-Contrast Imaging with the GMT

Johanan CODONA — 2011-07-11T22:24:12Z

Authors

Johanan L. Codona

Affiliations

Univ of Arizona, Steward Observatory

Abstract

High-contrast detection and characterization are plagued by subtle telescope imperfections and non-common-path (NCP) aberrations, leading to many long-lived speckles in the search area near a star. These can be corrected using the AO DM, but the complex halo of the star must be known in the science camera focal plane in order to compute the DM corrections. Phase-sorting Interferometry (PSI) is a technique to measure the science path halo on-sky and has been demonstrated at the MMT in the L and M band. PSI makes an interferometric measurement of the halo including NCP aberrations without the use of any extra hardware or sensing light introduced into the focal plane. The only requirement is that the science camera be read out fast enough to image the varying speckle intensities over the region of interest near the star. The PSI method uses the AO system's wavefront sensor telemetry to estimate the residual wavefront error over a series of synchronized science camera exposures, and a mathematical model of the telescope to compute the phase and amplitude of the dynamic halo speckles. The computed speckle phases are used to analyze the science frames into four statistical interferograms which are combined in the usual way to derive the complex halo in the science focal plane. This allows calculation of a DM correction update, enabling a halo-suppression closed-loop to be implemented. We explore the potential for using this method with the GMT AO system and simulate a GMT anti-halo servo for various near-to-mid infrared bands combined with a 6-decade high-contrast phase-apodization coronagraph implemented using machined phase plates. The result is a robust, low-overhead, easy-to-use, high-contrast imaging technique suitable for both search and spectral characterization very near stars.

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.

Pathfinders to ELT AO at W.M. Keck Observatory

Peter WIZINOWICH — 2011-07-11T22:07:38Z

Submitted by Peter Wizinowich

Authors

Peter Wizinowich

Affiliations

W.M. Keck Observatory

Abstract

The Keck II AO system has been extremely productive scientifically with more than 300 refereed science papers including over 100 obtained with LGS AO. We will discuss lessons learned for ELT AO from the existing system and from the soon to be completed Keck I LGS AO system, as well as from pathfinder development efforts including a near-IR tip-tilt sensor, PSF reconstruction efforts and the Observatory's next generation AO system.

MEMS Deformable Mirrors in Astronomical AO

Paul BIERDEN — 2011-07-05T12:22:40Z

Submitted by P. Bierden

Authors

Paul Bierden (1), Steven Cornelissen(1), Charlie Lam(1), and Thomas Bifano (1,2)

Affiliations

(1) Boston Micromachines Corporation, Cambridge, MA 02138 (2) Boston University, Boston, MA 02215

Abstract

As the development of adaptive optics instrumentation for Extremely Large Telescopes continues, the need for specialized deformable mirror grows. We report on the development of Boston Micromachines' micro-electromechanical (MEMS) deformable mirrors to meet these needs and the needs of other astronomical AO projects. Specific DM technologies will be discussed including the 4092 element continuous membrane mirror designed and built for the Gemini Planet Imager as well as a 2000 actuator DM being built for general high contrast astronomical AO applications. Also discussed will be a project to design and manufacture a 1021 hexagonal segment (3063 actuator) tip-tilt-piston DM for NASA's Planet Finding Mission. Design considerations, improvements in reliability, and device characteristics will be discussed. Performance results and plans for future mirrors development and how they fit into AO for ELT will be presented.