AO4ELT 2

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.

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.

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.