AO4ELT 2

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.

The Pyramid WFS with extended reference source

Enrico PINNA — 2011-05-19T21:19:09Z

Submitted by S. Esposito

Authors

Enrico Pinna, Alfio Puglisi, Javier Argomedo, Fernando Quiros-Pacheco, Armando Riccardi, Simone Esposito

Affiliations

Osservatorio di Arcetri

Abstract

During the LBT FLAO commissioning, the Pyramid Wave-Front Sensor (PWFS) demonstrated on sky its potential as component of a NGS SCAO system. These results confirmed the expected PWFS sensitivity in presence of a point-like guide source. The performances of the PWFS using an extended object as reference in astronomical applications have not yet been deeply investigated. In this work we show some preliminary laboratory result obtained on the LBT FLAO system #2 operated using an extended reference sources of diameter up to 1.6”. During the tests, as expected, the PWFS showed a sensitivity reduction due to the reference source extension. The sensitivity reduction only affects modes below a given radial order, leaving the sensitivity of the higher order modes unaffected. The limiting radial order increases with the reference source diameter. Our result suggests that AO systems, with an actuator pitch FLAO-like (30cm) and using a PWFS, can deliver high contrast images in H and K bands using reference object with diameter less than 1” and integrated Rmag < 9.5. The achieved result will be discussed in the framework of the ELTs AO systems and in context of LGS wavefront sensing.

Tip-tilt wavefront sensing from a coronagraphic image: laboratory demonstration with a four-quadrant phase mask.

Marion MAS — 2009-02-28T23:00:00Z

Submitted by Marion MAS

Authors

Marion Mas, Pierre Baudoz, Gérard Rousset, Raphaël Galicher

Affiliations

Observatoire de Paris-Meudon

Herzberg Institute of Astrophysics, NRC-CNRC

Abstract

Direct detections of exoplanets at wide separations requires high contrast imaging. A coronagraph can be used to suppress the overhelming light of the hosting star and detect its faint neighborhood. Neverthless, low order wavefront errors such as tip-tilt catastrophically affect the coronagraph performance. Classical wavefront sensors unfortunately need a dedicated channel and are thus subject to non-common path errors. We propose a method to estimate the tip-tilt errors upstream a four-quadrant phase mask coronagraph with no such non-common path aberrations. To do so, we directly use the coronagraphic image and measure the intensity variations induced by tip-tilt errors. We applied this technique on our laboratory high contrast imaging bench and could stabilize the beam position on the coronagraphic mask with a 0.05L/D accuracy. In our presentation, we will develop the technique formalism and present the laboratory results in detail.

The ARGOS wavefront sensor pnCCD camera for an ELT: characteristics, limitations and applications

Gilles ORBAN DE XIVRY — 2009-02-28T23:00:00Z

Submitted by Gilles ORBAN DE XIVRY

Authors

G. Orban de Xivry(1), S. Ihle(2), J. Ziegleder(1), L. Barl(1), R. Hartmann(2), S. Rabien(1), H. Soltau(2), L. Strueder(3)

Affiliations

(1) MPE, Giessenbachstrasse, 85748 Garching, Germany (2) PNSensor GmbH, Roemerstrasse 28, 80803 Muenchen, Germany (3) MPI Halbleiterlabor, Muenchen, Germany

Abstract

From low-order to high-order AO, future wave front sensors on ELTs require large, fast, and low-noise detectors with high quantum efficiency and low dark current. While a detector for a high-order Shack-Hartmann WFS does not exist yet, the current CCD technology pushed to its limits already provides several solutions for the ELT AO detector requirements. One of these devices is the new WFS pnCCD camera of ARGOS, the Ground-Layer Adaptive Optics system (GLAO) for LUCIFER at LBT. Indeed, with its 264x264 pixels, 48 mu m pixel size and 1kHz frame rate, this camera provides a technological solution to different needs of the AO systems for ELTs, such as low-order but as well possibly higher order correction using pyramid wavefront sensing. In this contribution, we present the newly developped WFS pnCCD camera of ARGOS and how it fulfills future detector needs of AO on ELTs.

Sky coverages on ELTs with a reference area much larger than the compensated one

Valentina VIOTTO — 2009-02-28T23:00:00Z

Submitted by Valentina VIOTTO

Authors

Viotto, V. (a,b), Ragazzoni, R. (a), Arcidiacono, C. (c), Dima, M. (a), Magrin, M. (a), Farinato, J. (a)

Affiliations

a - INAF, Astronomical Observatory of Padova b - University of Padova - Astronomy Department c - INAF, Astronomical Observatory of Arcetri

Abstract

Sky coverage for MCAO systems has been the subject of a large number of studies in the past decade or so. The resulting figures, further to have the chance of being refined by actual measurements carried out at the largest 8m class telescopes, have to be updated and validated for the most recent approaches in ELT adaptive optics corrections. In particular, techniques employing the use of several virtual deformable mirrors can take advantage of a field of view, inside which references can be found, that is much larger than the area where the correction is actually made. While a parallel with similar studies for Multi Objects AO can be traced down, we revise here the various proposed approaches and we show the results of similar computations using the novel concepts and gauging the outcome with the more recent on-sky available data. The comparison with similar computations that can be made for artificially generated beacon is briefly discussed.

Pyramid based locally closed loop wavefront sensor: an optomechanical study.

Demetrio MAGRIN — 2009-02-28T23:00:00Z

Submitted by Demetrio MAGRIN

Authors

Magrin D. (a), Dima M. (a), Farinato J. (a), Ragazzoni R. (a), Viotto, V. (a)(b)

Affiliations

a) INAF - Osservatorio Astronomico di Padova b) Universita' di Padova - Dipartimento di Astronomia

Abstract

Pyramid wavefront sensors have shown their ability to achieve ultimate performances in terms of usage of starlight photons. Several of these advantages, however, does relay on the fact that the starlight is focused onto the pyramid pin after being properly corrected. While conventional adaptive optics systems (including multi conjugated ones) automatically imply such a feature this is not true for Multi Objects or non conventional Multi Conjugated AO systems, or more in general for the ones where the compensated area is somehow different from the area searched for references. We develop the concept of locally closed loop systems in a compact way along with various approaches to metrologically measure the wavefront with enough absolute accuracy, in contrast with the accuracy to vanish the residual in the conventional use of wavefront sensors. We show an optomechanical study including a preliminary error budget and a choice of existing components in order to achieve the goal of detailed wavefront sensing with high dynamic range on the faintest references where a pyramid sensor can achieve significant results.

Mach-Zehnder Wavefront sensing in the context of Extreme Adaptive Optics on Extremely large telescopes

Maud LANGLOIS — 2009-02-28T23:00:00Z

Submitted by Maud LANGLOIS

Authors

M. Langlois, M. Tallon, E. Thiébaut

Affiliations

CENTRE DE RECHERCHE ASTROPHYSIQUE DE LYON

Abstract

We present results on the use of the Mach-Zehnder wavefront sensor in the context of Extreme Adaptive Optics (EXAO) on ELTs. Thanks to a very good sensitivity at high spatial frequencies, such wavefront sensor favors a clean correction of the starlight halo at small angular separations where the most demanding contrast is required, but its use is hampered by its non-linear response. It has already been studied in the context of 8m-class telescope (Langlois 2001) and shows very low noise propagation. In this paper we concentrate on the development of analytical and numerical modeling of the Mach-Zehnder in the ELTs context. This work is preparatory to the development of new methods for fast reconstruction with this type of wavefront sensor based on the sparseness advantage and Fractal Iterative method (Béchet, 2006) and the study of the inverse approach to unable very large dynamic wavefront measurement.

AOLI: Wavefront curvature sensor algorithms and their performance at low photon numbers

Jonathan CRASS — 2009-02-28T23:00:00Z

Submitted by Jonathan CRASS

Authors

Jonathan Crass (1), Bruno Femenía (2,3), David King (1), Craig Mackay (1), Rafael Rebolo (2,4), Lucas Labadie (5), Antonio Pérez Garrido (6), Marc Balcells (2,7), Anastasio Díaz-Sánchez (6), Jesús J. Fuensalida (2,3), Roberto López (2), Alex Oscoz (2), Jorge A. Pérez Prieto (2,3), Luis F. Rodríguez (2), Isidro Villó (6)

Affiliations

(1) Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK (2) Instituto de Astrofísica de Canarias, C/ Vía Láctea S/N, E-38200 La Laguna, Spain (3) Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain (4) Consejo Superior de Investigaciones Científicas, Spain (5) I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50397 Köln, Germany (6) Universidad Politécnica de Cartagena, Campus Muralla del Mar, Cartagena, Murcia E-30202, Spain (7) Isaac Newton Group of Telescopes, Apartado de Correos 321, E-38700 Santa Cruz de la Palma, Canary Islands, Spain

Abstract

The combined techniques of Lucky Imaging and low-order Adaptive Optics (AO) have already delivered diffraction limited images in the visible (35 milliarcsecond resolution in the I band on a 5 metre ground-based telescope). The need to be able to work at this resolution for a wide range of astronomical problems requires significant sky coverage using natural guide stars fainter than 18th magnitude. The Adaptive Optics Lucky Imager (AOLI) combines Lucky Imaging and low-order AO to provide diffraction limited imaging using a single instrument.

AOLI comprises a camera similar to the 'LuckyCam' developed at the Institute of Astronomy, University of Cambridge. The camera uses a 2x2 array of 1k square electon multiplying CCDs providing a corrected field of view of 30-120 arcseconds in diameter. The low-order Adaptive Optics component of AOLI employs a quad plane wavefront curvature sensor to determine wavefront distortions (Guyon, 2010) combined with a deformable mirror to apply corrections. This method allows faint natural guide stars to be used which is of key importance for milliarcsecond imaging at visible wavelengths.

Current work focuses primarily on the development of hardware and software algorithms for the AO system. The specifications for the system are presented with a discussion of the wavefront reconstruction algorithms, their performance and the requirement for high performance computing (e.g. GPUs). Characterising the effects of the curvature sensor at very low photon numbers is ongoing with a view to performing experimental comparisons with traditional Shack Hartmann sensors.