Publications of the MPIfR
Optical & Infrared
Interferometry Group
Bertram, T., Andersen, D., Arcidiacono,
C., Straubmeier, C., Eckart, A., Beckmann, U., Herbst, T.M
The LINC-NIRVANA Fringe and Flexure Tracking
System: differential piston simulation and detection
New Frontiers in Stellar Interferometry,
Proceedings of SPIE Volume 5491.
Edited by Wesley A. Traub. Bellingham, WA: The International Society
for Optical Engineering, 2004., p.1454
Abstract
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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