Some Characteristics of the E-ELT Sodium LGSs
N. Moussaoui, F. Djaidri, F. Zohra Ouanoufi
University of Sciences and Technology Houari Boumediene (USTHB), Faculty of Physics, Quantum Electronic Laboratory, Algiers, Algeria
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Adaptive optics systems require a source of light to measure and to correct wave-front distortions. This reference source of light must be in the field of view of the astronomical subject observed by the ground based telescope. There are not enough natural stars that could be used by the adaptive optics systems. In order to insure a full sky coverage of adaptive optics system beam tuned to the sodium D2 line at 589 nm. The characteristics of the sodium laser guide stars depend on the laser beam intensity, the laser beam polarization, the properties of the mesospheric sodium layer, the atmospheric transmission, and the geomagnetic field characteristics. For the properties of the mesospheric sodium layer we are interested in this study on the sodium layer column abundance, the centroid height, the sodium concentration, and the layer thickness. This part of our work is based on measurements of the mesospheric sodium layer characteristics which cover a long period at latitude 23° south, in São José dos Compos, São Paulo, Brazil. This latitude is approximately the same as for the European Extremely Large Telescope site (Paranal, Chile), which is located at latitude 24° south. The geomagnetic field effect is deduced from semi-empirical model realized by the Star Fire Optical Rang team and generalized by the European Southern Observatory Laser Guide Star Group. This work presents some characteristics of the sodium laser guide stars that could be created for the European-Extremely Large Telescope.

topics: adaptive optics, extremely large telescope, sodium-LGSs