13 September 2012 Aligning a more than 100 degrees of freedom wavefront sensor
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Abstract
LINC-NIRVANA is the Fizeau beam combiner for the LBT, with the aim to retrieve the sensitivity of a 12m telescope and the spatial resolution of a 22.8m one. Despite being only one of the four wavefront sensors of a layer-oriented MCAO system, the GWS, which is retrieving the deformation introduced by the lower atmosphere, known to be the main aberration source, reveals a noticeable internal opto-mechanical complexity. The presence of 12 small devices used to select up to the same number of NGSs, with 3 optical components each, moving in a wide annular 2'-6' arcmin Field of View and sending the light to a common pupil re-imager, and the need to obtain and keep a very good super-imposition of the pupil images on the CCD camera, led to an overall alignment procedure in which more than a hundred of degrees of freedom have to be contemporary adjusted. The rotation of the entire WFS to compensate for the sky movement, moreover, introduces a further difficulty both in the alignment and in ensuring the required pupil superposition stability. A detailed description of the alignment procedure is presented here, together with the lessons learned managing the complexity of such a WFS, which led to considerations regarding future instruments, like a possible review of numerical versus optical co-add approach, above all if close to zero read-out noise detectors will be soon available. Nevertheless, the GWS AIV has been carried out and the system will be soon mounted at LBT to perform what is called the Pathfinder experiment, which consists in ground-layer correction, taking advantage of the Adaptive Secondary deformable Mirror.
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Luca Marafatto, Luca Marafatto, Maria Bergomi, Maria Bergomi, Alessandro Brunelli, Alessandro Brunelli, Marco Dima, Marco Dima, Jacopo Farinato, Jacopo Farinato, Giancarlo Farisato, Giancarlo Farisato, Luigi Lessio, Luigi Lessio, Demetrio Magrin, Demetrio Magrin, Roberto Ragazzoni, Roberto Ragazzoni, Valentina Viotto, Valentina Viotto, Thomas Bertram, Thomas Bertram, Peter Bizenberger, Peter Bizenberger, Matthieu Brangier, Matthieu Brangier, Florian Briegel, Florian Briegel, Albert Conrad, Albert Conrad, Fulvio De Bonis, Fulvio De Bonis, Tom Herbst, Tom Herbst, Ralph Hofferbert, Ralph Hofferbert, Frank Kittmann, Frank Kittmann, Martin Kürster, Martin Kürster, Daniel Meschke, Daniel Meschke, Lars Mohr, Lars Mohr, Ralf-Rainer Rohloff, Ralf-Rainer Rohloff, } "Aligning a more than 100 degrees of freedom wavefront sensor", Proc. SPIE 8447, Adaptive Optics Systems III, 84476F (13 September 2012); doi: 10.1117/12.926773; https://doi.org/10.1117/12.926773
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