20 October 2004 The fringe and flexure tracking system for LINC-NIRVANA: basic design and principle of operation
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LINC-NIRVANA is the interferometric near-infrared imaging camera for the Large Binocular Telescope (LBT). Operating at JHK bands LINC-NIRVANA will provide an unique and unprecedented combination of high angular resolution (~9 milliarcseconds at 1.25 µm), wide field of view (~100 arcseconds2 at 1.25 µm), and large collecting area (~100 m2). One of the major contributions of the I. Physikalische Institut of the University of Cologne to this project is the development of the Fringe and Flexure Tracking System (FFTS). In close cooperation with the Adaptive Optics systems of LINC-NIRVANA the FFTS is a fundamental component to ensure a complete and time-stable wavefront correction at the position of the science detector in order to allow for long integration times at interferometric angular resolutions. Using a dedicated near-infrared detector array at a combined focus close to the science detector, the Fringe and Flexure Tracking System analyses the interferometric point spread function (PSF) of a suitably bright reference source at frame rates of several hundred Hertz up to 1 kHz. By fitting a parameterized theoretical model PSF to the preprocessed image-data the FFTS determines the amount of pistonic phase difference and the amount of an angular misalignment between the wavefronts of the two optical paths of LINC-NIRVANA. For every exposure the correcting parameters are derived in real-time and transmitted to the respective control electronics, or the Adaptive Optics systems of the single-eye telescopes, which will adjust their optical elements accordingly. In this paper we present the opto-mechanical hardware design, the principle of operation of the software control algorithms, and the results of first numerical simulations and laboratory experiments of the performance of this Fringe and Flexure Tracking System.
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Christian Straubmeier, Thomas Bertram, Andreas Eckart, Yibing Wang, Lahbib Zealouk, Thomas M. Herbst, David R. Andersen, Roberto Ragazzoni, Gerd P. Weigelt, "The fringe and flexure tracking system for LINC-NIRVANA: basic design and principle of operation", Proc. SPIE 5491, New Frontiers in Stellar Interferometry, (20 October 2004); doi: 10.1117/12.551113; https://doi.org/10.1117/12.551113




Adaptive optics

Point spread functions

Control systems



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