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Proceedings Paper

Beam quality and polarization analysis of the ALFA laser at Calar Alto and the influence on brightness and size of the laser guide star
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Paper Abstract

The ALFA-Laser of the MPE/MPIA adaptive optic system utilizes a 4W cw-laser for the creation of a sodium layer guide star. The artificial star serves as a reference source for the adaptive optics system installed at the Calar Alto observatory in souther Spain. Several distortion sources are affecting the laser beam and result in a laser guide star spot size too large on which to lock the adaptive optics loop properly. Therefore a number of analysis tools have been installed just before the laser beam expander and measurements of the beam quality have been performed. In this contribution we present parts of the experimental setup and results of these measurements. In addition we report on experimental studies of the guide star brightness when exciting the sodium layer with different polarization states of the laser radiation. A surprisingly large gain in response flux, when using circular polarization, has been measured. The complicated behavior of the polarization state with telescope position, due to phase changes at the beam relay mirrors, makes a control loop necessary to keep the projected beam optimal.

Paper Details

Date Published: 27 September 1999
PDF: 10 pages
Proc. SPIE 3762, Adaptive Optics Systems and Technology, (27 September 1999); doi: 10.1117/12.363594
Show Author Affiliations
Sebastian Rabien, Max-Planck-Institut fuer Extraterrestrische Physik (Germany)
Richard I. Davies, Max-Planck-Institut fuer Extraterrestrische Physik (Germany)
Wolfgang K. P. Hackenberg, Max-Planck-Institut fuer Extraterrestrische Physik (Germany)
Andreas Eckart, Max-Planck-Institut fuer Extraterrestrische Physik (Germany)
Thomas Ott, Max-Planck-Institut fuer Extraterrestrische Physik (Germany)
David James Butler, Max-Planck-Institut fuer Extraterrestrische Physik (Germany)

Published in SPIE Proceedings Vol. 3762:
Adaptive Optics Systems and Technology
Robert K. Tyson; Robert Q. Fugate, Editor(s)

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