20 October 2004 The LINC-NIRVANA fringe and flexure tracking system: differential piston simulation and detection
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The correction of atmospherical differential piston and instrumental flexure effects is mandatory for full interferometric performance of the LBT NIR interferometric imaging camera LINC-NIRVANA. This is the task of the Fringe and Flexure Tracking System (FFTS), which is part of the contribution of the I. Physikalische Institut of the University of Cologne to the project. Differential piston and flexure effects will be detected and corrected in a real-time closed loop by analyzing the PSF of a guide star at a frequency of up to several hundred Hz. Numerous critical design parameters for both FFTS hardware and control loop have to be derived from simulations. Detailed knowledge of the special shape of the LBT interferometric PSF as a function of a variety of parameters is required to design the fringe tracking control loop. In this paper we will show the results of our software that allows us to generate polychromatic interferometric PSFs for a number of different scenarios. Our fringe detection algorithm is based on an analytic model which is fitted to the acquired PSF. We present the results of the evaluation of the algorithm in terms of speed and residual piston, as well as the first successful implementation of the algorithm in a closed loop system. Simulations of the time evolution of differential piston have been performed in order to investigate necessary correction frequencies and the variation of differential piston across the usable field of view. These simulations are based on the Layer Oriented Adaptive Optics performance simulator "LOST" of the Osservatorio Astriofisico di Arcetri.
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Thomas Bertram, David R. Andersen, Carmelo Arcidiacono, Christian Straubmeier, Andreas Eckart, Udo Beckmann, and Thomas M. Herbst "The LINC-NIRVANA fringe and flexure tracking system: differential piston simulation and detection", Proc. SPIE 5491, New Frontiers in Stellar Interferometry, (20 October 2004); doi: 10.1117/12.551312; https://doi.org/10.1117/12.551312

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