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.

Latest Ground Layer Adaptive Optics results and advancements in Laser Tomography implementation at the 6.5m MMT telescope

Eduardo BENDEK — 2011-05-20T07:26:54Z

Submitted by E. Bendek

Authors

Eduardo Bendek, Michael Hart, Keith Powell, Vidhya Vaitheeswaran, Don McCarthy, Craig Kulesa

Affiliations

University of Arizona

Abstract

Laser tomography capability using the Multi Laser Guide Star system is being implemented at the 6.5 m MMT telescope on Mt. Hopkins AZ. The system uses five range gated and dynamically refocused Rayleigh laser beacons to perform the tomographic sampling of the atmosphere. Corrections are then applied to the wavefront using the 336-actuator adaptive secondary mirror of the telescope. We present the latest results obtained using the GLAO mode, using for the first time, a plate scale on our IR science camera that samples the diffraction scale at the Nyquist limit. We find a reduction in the width of the on-axis point-spread function from 1.1” to <0.2” in H band. In addition, progress toward Laser Tomography is presented using an approach in which a minimum mean square reconstructor matrix is computed from simultaneous measurements recorded by the LGS wavefront sensor and a ground-truth NGS sensor. This paper also discusses our approach to estimate the turbulence intensity distribution Cn2, which is essential to our goal to build tomographic reconstructor matrices with an analytic forward model, to be updated on the fly during regular observing.

Vibration Suppression Algorithms for NFIRAOS on TMT

Carlos CORREIA — 2011-05-17T15:01:54Z

Submitted by C. Correia

Authors

C. Correia (a) , J.-P. Véran (a) , G. Herriot (a) , B. Ellerbroek (b), L. Wang (b), L. Gilles (b)

Affiliations

a – Herzberg Institute of Astrophysics; b – Thirty Meter Telescope

Abstract

Vibration suppression in Astronomical Adaptive Optics (AO) systems has gathered great attention in the context of next-generation instrumentation for current telescopes and future Extremely Large Telescopes (ELTs). This paper focus on the application of a novel multi-rate algorithm formulated in [Correia et al 2011][1] to the 1st-light Multi-Conjugate Adaptive Optics Facility (NFIRAOS) for the Thirty-Meter Telescope (TMT).

Numerical results cover the case of several vibration peaks with variable peak width based on telemetry from the Keck observatory. This algorithm is compared to other two solutions at sampling frequencies in the range [20–800] Hz, required to sense stars with magnitudes from mv=12 − 22 in H-band. Efficient methods to identify vibrations from closed-loop telemetry data are also discussed.

The Slope-Oriented Hadamard scheme for in-lab or on-sky interaction matrix calibration

Serge MEIMON — 2011-05-16T20:00:22Z

submitted by S. Meimon

Authors

Serge Meimon, Thierry Fusco, Cyril Petit

Affiliations

ONERA

Abstract

The correct calibration of the interaction matrix affects the performance of an adaptive optics system. In the case of high-order systems, when the number of mirror modes is worth a few thousands, the calibration strategy is critical to reach the maximum interaction matrix quality in the minimum time. This is all the more true for the E-ELT, for which on sky calibration procedures have to be considered. Here, we first build a tractable interaction matrix quality criterion. We then propose the Slope-Oriented Hadamard scheme which optimizes this quality criterion.

We demonstrate that for a given level of quality, the calibration time needed using the Slope-Oriented Hadamard method is ten times less than with a classical Hadamard scheme. These analytical and simulation results are confirmed experimentally both on the ONERA AO bench (BOA) and on the SPHERE XAO system (SAXO).

Last, we show how to use this method in an on-sky calibration scheme, and we quantify the gain in time compared to other calibration strategies.

Performance of MCAO on the E-ELT using the Fractal Iterative Method for fast atmospheric tomography

Michel TALLON — 2009-02-28T23:00:00Z

Submitted by Michel TALLON

Authors

Michel Tallon, Clémentine Béchet, Isabelle Tallon-Bosc, Miska Le Louarn, Éric Thiébaut, Richard Clare, Enrico Marchetti

Affiliations

1, 3, 5: Centre de Recherche Astrophysique de Lyon, France

2, 4, 6, 7: European Southern Observatory, Germany

Abstract

Adaptive optics (AO) on Extremely Large Telescopes (ELTs) must overcome the difficulty of solving a huge number of equations in real time, especially when atmospheric tomography is involved. This is particularly the case for multi-conjugate or multi-objects AO systems. The Fractal Iterative Method (FrIM) has been introduced as a fast iterative algorithm for minimum variance wavefront reconstruction and control on ELTs. In particular, it includes an accurate fast computation of turbulence priors by using the so-called fractal operator.

We present the first results obtained with FrIM in closed-loop in the context of atmospheric tomography. The method has been tested on Octopus, the end-to-end AO simulator at ESO, by considering MAORY, the multi-conjugate AO module planed for the E-ELT. This module aims at correcting a 2 arcmin field-of-view, by using 3 deformable mirrors, 6 Sodium laser guide stars, and 3 natural guide stars for low-order wavefront sensing.

We show the performance obtained in different conditions and analyze the effect of some parameters of FrIM, like the weight of the priors, or the number of conjugate gradient iterations for solving the reconstruction. We show how the duration of the simulations can be shortened on such a large aperture, with the introduction of artificial vibrations in the simulation. The results are also compared to a more classical approach using matrix-vector multiplication.

Using artificial neural networks (ANN) for open-loop tomography

Richard MYERS — 2009-02-28T23:00:00Z

Submitted by James OSBORN

Authors

James Osborn, Francisco Javier De Cos Juez, Dani Guzman, Timothy Butterley, Richard Myers, Andres Guesalaga and Jesus Laine

Affiliations

Universidad Catolica, Univeristy of Durham and Universidad de Oviedo

Abstract

The next generation of adaptive optics (AO) systems require tomographic techniques in order to correct for atmospheric turbulence along lines of sight separated from the guide stars. Multi-object adaptive optics (MOAO) is one such technique. Here, we present a method which uses an artificial neural network (ANN) to reconstruct the target phase given off-axis references sources. This method does not require any input of the turbulence profile and is therefore less susceptible to changing conditions than some existing methods. We compare our ANN method with a standard least squares type matrix multiplication method (MVM) in simulation and find that the tomographic error is similar to the MVM method. In changing conditions the tomographic error increases for MVM but remains constant with the ANN model and no large matrix inversions are required.

Real time control zonal algorithm for adaptive optical system

Irina SERGIEVSKAYA — 2009-02-28T23:00:00Z

Submitted by Irina SERGIEVSKAYA

Authors

I.Sergievskaya, S.Royo, J.Riu, M.Ares

Affiliations

CD6-UPC

Abstract

An attempt was made to develop a zonal real time control algorithm for adaptive optical system based on block tridiagonal control matrix. Efficiency of a zonal approach for AOS with large number of actuators and local nature of response functions was studied using mathematical modeling and compared to classical modal least square solution and iterative methods. Calculation efficiency and residual wavefront error are examined. Turbulent media aberration was simulated using Von Karman model. Experimental realization using available 37 actuators piezoelectric DM and Shack-Hartmann wavefront sensor was performed for mathematical model validation.

The effect of the instrument environment on the Altair AO system

Julian CHRISTOU — 2009-02-28T23:00:00Z

Submitted by Julian CHRISTOU

Authors

Julian Christou, Benoit Neichel, Francois Rigaut

Affiliations

Gemini Observatory

Abstract

The Altair AO system at Gemini North has been in regular operation for many years. Over the past few years we have been routinely monitoring its performance looking at the telemetry circular buffers from the nightly tuning, in particular the residual tip-tilt (TT). We present analysis of these data which illustrate how the instrument support structure (ISS) environment affects the residual TT and how different components of the TT signal is affected by the instrument compliment.

LINC-NIRVANA Derotators

Frank KITTMANN — 2009-02-28T23:00:00Z

Submitted by Frank KITTMANN

Authors

Frank Kittmann, Thomas Bertram, Al Conrad, Jan Trowitzsch, Florian Briegel, Juergen Berwein, Lars Mohr

Affiliations

MPIA

Abstract

The near infrared interferometer LINC-NIRVANA combines the beams coming from the two primary mirrors of the Large Binocular Telescope to increase the resolution of the science camera image. LINC-NIRVANA is using layer-oriented multi-conjugate adaptive optics (MCAO) to reduce the influence of the atmospheric turbulence. The deformable mirrors of the MCAO systems are conjugated to the ground layer and a second layer in the upper atmosphere, respectively. Ground layer wavefront sensors and high layer wavefront sensors measure the wavefront in these two layers. Due to geometrical constraints unique to this type of instrument, it is not possible to provide a single derotator at the entrance of each incoming beam. Due to that fact, field derotation has to be applied for each wavefront sensor and for the science detector separately. The fields of the high layer wavefront sensors are derotated by the use of K-Mirrors, whereas the ground layer wavefront sensors and the science detector rotate themselves to compensate the field rotation. The derotation axes of the derotators will not perfectly match the field rotation center and projected derotation axis. These resulting effects have to be considered in the tip/tilt control strategy. In this paper we will describe the degree of accuracy required for the field derotation and compare that requirement with our test results. This includes timing and positioning accuracy over the complete derotation trajectory.

End-To-End performance test of the LINC-NIRVANA Wavefront-Sensor system.

Juergen BERWEIN — 2009-02-28T23:00:00Z

Submitted by Juergen BERWEIN

Authors

Juergen Berwein, Thomas Bertram, Al Conrad, Florian Briegel, Frank Kittmann, Xiangyu Zhang, Lars Mohr

Affiliations

Max Planck Institute for Astronomy

Abstract

LINC-NIRVANA is an imaging Fizeau interferometer, for use in near infrared wavelengths, being built for the Large Binocular Telescope. Multi-conjugate adaptive optics (MCAO) increases the sky coverage and the field of view over which diffraction limited images can be obtained. For its MCAO implementation, Linc-Nirvana utilizes four total wavefront sensors; each of the two beams is corrected by both a ground-layer wavefront sensor (GWS) and a high-layer wavefront sensor (HWS). The GWS controls the adaptive secondary deformable mirror (DM), which is based on an DSP slope computing unit. Whereas the HWS controls an internal DM via computations provided by an off-the-shelf multi-core Linux system. Using wavefront sensor data collected from a prior lab experiment, we have shown via simulation that the Linux based system is sufficient to operate at 1kHz, with jitter well below the needs of the final system. Based on that setup we tested the end-to-end performance and latency through all parts of the system which includes the camera, the wavefront controller, and the deformable mirror. We will present our loop control structure and the results of those performance tests.