In the framework of the studies related to the European Extremely Large Telescope (E-ELT), a fundamental importance must be given to Sodium Laser Guide Stars (LGS) Wavefront Sensing which is essential to permit wide correction uniformity and a relevant sky coverage. The finite distance of the sodium layer where the LGSs form, its width and density time variability, requires detailed studies in order to better perform the wavefront measurement. Many LGS peculiar problems, such as perspective elongation, focus uncertainty and launching angle , that can be neglected or more easily managed for 8m class telescopes, become fundamental issues in the design of future LGS Wave-Front Sensors (WFSs) for the E-ELT. In this paper we present the LGS WFS prototype built at the Osservatorio Astronomico di Bologna reproducing the expected conditions of a E-ELT like LGS Shack-Hartmann WFS. The main scope of the prototype is to cross check the simulations concerning the centroiding algorithms in the case of elongated spots using different light intensities, pixel scales, spot offsets, sub-aperture Field of Views and elongated source intensity profiles. Starting from the conceptual idea we show the system design and the integration in the lab. Finally the prototype optical quality and its capability to perform the required tests are presented.

Date Published: 27 July 2010
PDF: 7 pages
Proc. SPIE 7736, Adaptive Optics Systems II, 77365E (27 July 2010); doi: 10.1117/12.857975

Published in SPIE Proceedings Vol. 7736:
Adaptive Optics Systems II
Brent L. Ellerbroek; Michael Hart; Norbert Hubin; Peter L. Wizinowich, Editor(s)