AO4ELT 2

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.

Advancement of Piezo-Stack DM technology at CILAS: Example of HODM for KIS Gregor Solar Telescope

Jean-Christophe SINQUIN — 2011-07-05T12:20:51Z

Submitted by J.C. Sinquin

Authors

J.C. Sinquin, A. Bastard, R. Cousty, C. Guillemard, H. Pagès

Affiliations

Cilas – 8, avenue Buffon, Z.I. La Source, 45063 Orléans

Abstract

Cilas has designed, manufactured and tested the deformable mirror for use in the high order adaptive optics system in the 1.5 m Gregor solar telescope (Tenerife). In the scope of this project for Kiepenheuer-Institut für Sonnenphysik (KIS), we have reached the smallest spacing ever made with our piezo-stack technology (3.2 mm) while increasing the overall reliability of our DMs by significant design evolutions. We will present the main specifications of the DM (18x18 actuator array, > 2 μm interactuator stroke, > 20 kHz main resonance frequency) and the study results on reliability. This study is focused on electrical and opto-mechanical stability of the DM vs. time. The improved piezo-stack technology will be used for next generation of DMs for large telescopes as TMT and ESO (VLT and E-ELT)

Contactless Large Deformable Mirrors: ELT AO corrector technology available now

Roberto BIASI — 2011-05-20T07:32:15Z

Submitted by R. Biasi

Authors

Roberto Biasi (1) Daniele Gallieni (2)

Affiliations

(1) Microgate (2) ADS International

Abstract

We present our design of ESO E-ELT M4 deformable mirror and GMT Adaptive Secondary Mirrors unit. Both systems are based on our consolidated design of large deformable mirrors for 8-m class telescopes, successfully implemented on MMT and LBT and currently in advanced construction and testing phase for VLT and Magellan telescopes respectively. We describe the main features of the technology adopted: thin Zerodur mirror shell with contactless voice coil motors, co-located capacitive sensors to close a local position loop at each actuator, centralized control by force feedforward, embedded real time control and communication electronics. We then highlight how the same concept has been scaled up on the E-ELT M4AU and the GMT-ASM cases, adapting the technology to deal with thousands of actuators, while maintaining its intrinsic advantages: tolerance to actuators' failures, mechanical de-coupling and relaxed tolerances between correcting mirror and reference structure, large stroke, hysteresis-free behavior. For the next generation systems, we report the predicted performances based on the actual results attained on our 1-m class DMs currently in use: the LBT adaptive secondary for the GMT-ASM and the 330 actuators Demonstration Prototype for the E-ELT M4AU.

Wavefront reconstruction for eXtreme Adaptive Optics

Iuliia SHATOKHINA — 2009-02-28T23:00:00Z

Submitted by Iuliia SHATOKHINA

Authors

M.Zhariy, R.Ramlau, A.Obereder

Affiliations

Institute for Industrial Mathematics, Johannes Kepler University Linz, A.Obereder - Mathconsult GmbH

Abstract

In this presentation, we report about the progress made on eXtreme Adaptive Optics (XAO) within the Austrian Adaptive Optics (AAO) group project Mathematical algorithms and software for E-ELT Adaptive Optics.

We consider the problem of wavefront reconstruction from the Pyramid wavefront sensor (P-WFS) measurements. First, we concentrate on the non-modulated Pyramid WFS case. A good reconstructor relies on a sufficiently good forward model, so analysis of the model is needed. We have studied two analytical models which can be found in the literature, with and without interference, and developed appropriate simulations. Under the closed loop assumption an approximation to the model involving Hilbert transforms has been derived. Our reconstruction algorithm is based on the inversion of the Hilbert transform. We present analytical proofs as well as numerical results for the algorithm.

In addition, a Pyramid WFS with circular modulation is considered. We have derived an analytical model without interference for the modulated Pyramid WFS case. The simulation can be easily extended from the non-modulated case by adding modulation tilts to the incoming phase.

Finally, the relations between the modulated Pyramid WFS and the more conventional Shack-Hartmann WFS as well as with the Roof WFS are discussed.

ELT oriented adaptive optics demonstration bench

Kacem EL HADI — 2009-02-28T23:00:00Z

Submitted by El hadi KACEM

Authors

K. El Hadi, B. LeRoux, M. NDiaye

Affiliations

Laboratoire d'Astrophysique de Marseille (LAM)

Abstract

We are developing an Adaptive Optics bench designed to validate experimentally new instrumental concepts dedicated to Extremely Large Telescopes (ELTs). Our AO bench is being developed with three main objectives. The first one concerns the experimental study of control solutions for two levels of correction systems, such as woofer-tweeter systems. Indeed, the use of two consecutive deformable mirrors (DM), necessary for most of AO insruments on E-ELT, rises correction and command problems to be optimized. Our two mirrors (a 140 actuators DM and a Phase Modulator LCoS mirror) are being fully characterized before closing the AO loop. The second goal is the experimental validation of the Pyramid Wave Front Sensor (PWFS) in ELTs conditions with a Laser Guide Star (LGS). The design of our PWFS is undergoing and the LGS tests will take place by the end of 2013. All these studies are led in collaboration with University of Bologna, ONERA and L2TI. The third and longer term application is the experimental validation of an optimized control law dedicated to the large number of degrees of freedom, based on Kalman filtering and studied at LAM. We present the optical design of the bench, the calibrations of the elements and the first experimental results.

Thin Shell Manufacturing for large Wavefront correctors

Eric RUCH — 2009-02-28T23:00:00Z

Submitted by Eric RUCH

Authors

Eric Ruch, Florence Poutriquet

Affiliations

Sagem Défense Sécurité

Abstract

One of the major key elements in large adaptive optical systems is the thin shell, used as a deformable mirror. Although the optical prescriptions are relaxed with respect to a passive mirror, especially in the low spatial frequency domain, other requirements, such as the cosmetic defects (scratch & dig), the tight control of the thickness uniformity and of course the fragility of the piece having an aspect ratio up to 1000:1, generate new problems during the manufacturing, testing and handling of such optics. Moreover, the optical surface has to be tested in two different ways: a classical optical test bench allows us to create a surface map of the mirror. This map is then computed to determine the force required by the actuators to flatten the mirror and this becomes also a specification for polishing and implies a good interaction with the voice coil manufacturer. More than twenty years ago Sagem – Reosc developed the first meter class thin shell for early adaptive optics experiments. Since then, large thin shell have been used as the optical part in composite mirrors and more recently the aspheric shell for the VLT Deformable Secondary Mirror has been polished and prototypes, up to scale 1, of the E-ELT M4 Adaptive Mirror have been delivered to ESO in 2010. This paper will present some recent results in the manufacturing and testing technologies of large this shell, especially focusing on the development of the 1,1 meter convex aspherical shell for the VLT M2 mirror and on the results obtained on the largest thin shell produced so far (2,5 meter in diameter) developed as a demonstrator for the future E-ELT M4.

Prototype Small Footprint Amplifier for Piezoelectric Deformable Mirrors

Kris CAPUTA — 2009-02-28T23:00:00Z

Submitted by Kris CAPUTA

Authors

Kris Caputa*, Glen Herriot*, Joel Niebergal** and Adam Zielinski**

Affiliations

* NRC Herzberg Institute of Astrophysics ** University of Victoria dept ECE

Abstract

AO subsystems of the ELT observatories will incorporate deformable mirrors with an order of magnitude larger number of piezoelectric actuators than the AO systems currently deployed. Simply scaling up the drive electronics that are presently available commercially would substantially drive up the AO cost, pose unacceptably high demands for the supply power and heat dissipation, and occupy large physical volume. We have set out to prototype a high voltage amplifier that is compact enough to allow packaging 100 amplifier channels on a single 6U Eurocard with the goal to have a DM drive channel density of 1200 per 6U VME crate. Individual amplifier circuits should be driven by a multichannel A/D converter, consume no more than 0.5W from the +/-400V power supply, be slew rate limited in hardware, and be short-circuit protected. The component cost should be an order of magnitude less than the integrated circuit high voltage amplifiers currently on the market. We started out with modeling candidate circuits in SPICE, then built physical prototypes using inexpensive off the shelf components. In this paper we present experimental results of exposing several prototype circuits to both normal operating conditions and foreseeable fault conditions. The performance is evaluated against the AO requirements for the output range and bandwidth and the DM actuator safety requirements.

Preliminary design status of the M4AU based on piezo-stack technology

Bruno CREPY — 2009-02-28T23:00:00Z

Submitted by Bruno CREPY

Authors

B Crepy (b), S Chaillot (g), JM Conan (d), R Cousty (b), C Delrez (c), M Dimmler (a), JL Dournaux (f), S De Zotti (e), E Gabriel (c), R Gasmi (f), R Grasser (b), N Hubin (a), P Jagourel (f), L Jochum (a), F Locre (b), P-Y Madec (a), P Morin (b), M Mueller (a), G Petit (d), D Petitgas (b), JJ Roland (b), JC Sinquin (b), E Vernet (a)

Affiliations

ESO (a) Karl-Schwarzschild-Strasse 2 - D-85748 Garching bei München CILAS (b) , 8 Avenue Buffon – BP 6319 - 45063 Orléans Cedex, France AMOS © Liege science park - Rue des Chasseurs Ardennais - 4031 Angleur, Belgium ONERA (d) BP72 - 29 avenue de la Division Leclerc - FR-92322 - Chatillon, France Astrium (e), 31, avenue des Cosmonautes - 31402 Toulouse, France Observatory of Paris Meudon (f), 5, place Jules Janssen, 92195 Meudon, France Boostec (g), Zone Industrielle - 65460 Bazet, France

Abstract

Cilas proposes a M4 adaptive mirror (M4AM) that corrects the atmospheric turbulence at high frequencies and residual tip-tilt and defocus due to telescope vibrations by using piezo-stack actuators. The design presents a matrix of 7217 actuators (hexagonal geometry, spacing equal to 29 mm) leading to a fitting error reaching the goal. The mirror is held by a positioning system which ensures all movements of the mirror at low frequency and selects the focus (Nasmyth A or B) using a hexapod concept. This subsystem is fixed rigidly to the mounting system and permits mirror displacements. The M4 control system (M4CS) ensures the connection between the telescope control/monitoring system and the M4 unit - positioning system (M4PS) and piezo-stack actuators in particular. This subsystem is composed of electronic boards, mechanical support fixed to the mounting structure and the thermal hardware. With piezo-stack actuators, most of the thermal load is minimized and dissipated in the electronic boards and not in the adaptive mirror. The mounting structure (M4MS) is the mechanical interface with the telescope (and the ARU in particular) and ensures the integrity and stability of M4 unit subsystems. M4 positioning system and mounting structure are subcontracted to Amos Company.

CuRe - A new wavefront reconstruction method for SH-WFS measurements

Andreas OBEREDER — 2009-02-28T23:00:00Z

Submitted by Andreas OBEREDER

Authors

Rosensteiner, Zhary, Neubauer, Ramlau, Obereder

Affiliations

Mathconsult GmbH (1,5) Insitut for Industrial Mathematics (2,3,4)

Abstract

In order to fulfill the real-time requirements for AO on ELTs, one has to either invest in (very) high performance hardware or spend some effort on the development of highly efficient reconstruction algorithms for wavefront sensors. The AAO (Austrian Adaptive Optics) team is involved in deriving wavefront reconstructors for SH- and Pyramid-WFS measurements utilizing the mathematical properties of the forward operators for these wavefront sensors. At the moment, we focus mainly on direct reconstructors with complexity O(n) (where n denotes the number of subapertures of the WFS) to make the reconstruction scalable for large telescopes. In this talk we will introduce a new algorithm, the Cumulative Reconstructor (CuRe), present its properties, namely error propagation of the method and the numerical effort for the reconstruction of the incoming wavefront, as well as first results concerning the quality of the method (dependent on different noise sources). Further improvements of the algorithm, especially a domain decomposition method for enhancing reconstruction quality and improving the overall speed of the algorithm will be presented and analyzed. A speed comparison with different wavefront reconstruction algorithms will be presented to point out the enormous gain of the new CuReD (Cumulative Reconstructor with Domain Decomposition) algorithm concerning numerical performance and applicability for real life telescope adaptive optics applications. In the outlook of the talk we will present first XAO results utilizing a variant of the CuReD for the reconstruction of modulated Pyramid WFS measurements.