EDP Sciences
Free access
Issue A&A
Volume 378, Number 2, November I 2001
Page(s) 710 - 721
Section Instruments, observational techniques and data processing
DOI http://dx.doi.org/10.1051/0004-6361:20011213



A&A 378, 710-721 (2001)
DOI: 10.1051/0004-6361:20011213

Optimized modal tomography in adaptive optics

A. Tokovinin1, 2, M. Le Louarn2, 3, E. Viard4, 2, N. Hubin2 and R. Conan2

1  Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
2  European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany
    e-mail: nhubin@eso.org; lelouarn@eso.org; rconan@eso.org
3  Center for Adaptive Optics, Kerr Hall, University of California, Santa Cruz, CA 95064, USA
    e-mail: lelouarn@ucolick.org
4  Astronomical Observatory of Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy
    e-mail: viard@pd.astro.it

(Received 20 April 2001 / Accepted 24 August 2001 )

Abstract
The performance of modal Multi-Conjugate Adaptive Optics systems correcting a finite number of Zernike modes is studied using a second-order statistical analysis. Both natural and laser guide stars (GS) are considered. An optimized command matrix is computed from the covariances of atmospheric signals and noise, to minimize the residual phase variance averaged over the field of view. An efficient way to calculate atmospheric covariances of Zernike modes and their projections is found. The modal covariance code is shown to reproduce the known results on anisoplanatism and the cone effect with single GS. It is then used to study the error of wave-front estimation from several off-axis GSs (tomography). With increasing radius of the GS constellation $\Theta$, the tomographic error increases quadratically at small $\Theta$, then linearly at larger $\Theta$ when incomplete overlap of GS beams in the upper atmospheric layers provides the major contribution to this error, especially on low-order modes. It is demonstrated that the quality of turbulence correction with two deformable mirrors is practically independent of the conjugation altitude of the second mirror, as long as the command matrix is optimized for each configuration.


Key words: instrumentation: adaptive optics -- atmospheric effects -- telescopes

Offprint request: A. Tokovinin, atokovinin@ctio.noao.edu




© ESO 2001

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)