27 September 1999 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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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.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sebastian Rabien, Richard I. Davies, Wolfgang K. P. Hackenberg, Andreas Eckart, Thomas Ott, and David James Butler "Beam quality and polarization analysis of the ALFA laser at Calar Alto and the influence on brightness and size of the laser guide star", Proc. SPIE 3762, Adaptive Optics Systems and Technology, (27 September 1999); doi: 10.1117/12.363594; https://doi.org/10.1117/12.363594
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