Publications of the MPIfR Optical & Infrared Interferometry Group
Straubmeier, C., Bertram, T., Eckart, A., Wang, Y., Zealouk, L., Herbst, T.M., Andersen, D.R., Ragazzoni, R., Weigelt, G
A fringe and flexure tracking system for LINC-NIRVANA: basic design and principle of operation
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.1486
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 ým), wide field of view (~100 arcseconds2 at
1.25 ým), 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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