Publications of the MPIfR
Optical & Infrared
Interferometry Group
Straubmeier, C., Bertram, T., Eckart,
A., Rost, S.
Wang, Y., Herbst, T., Ragazzoni, R., Weigelt, G.
The imaging fringe and flexure tracker of
LINC-NIRVANA:
basic opto-mechanical design and principle of operation
Advances in Stellar Interferometry
Proceedings of SPIE: Vol. 6268, p.62681I-(1-12)
Danchi, W., Monnier, J., Schöller, M. (eds.)
Abstract
LINC-NIRVANA is the interferometric near-infrared imaging camera for
the Large Binocular Telescope (LBT).
Being able to observe at wavelength bands from J to K (suppported by an
adaptive optics system operating at
visible light) LINC-NIRVANA will provide an unique and unprecedented
combination of high angular resolution
(~ 9 milliarcseconds at 1.25µm), wide field of view (~ 100 arcseconds2
at 1.25µm), and large collecting area
(~ 100 m2).
One of the major contributions of the 1. Physikalische Institut of the
University of Cologne to this project is
the development and provision of the Fringe and Flexure Tracking System
(FFTS). In addition to the single-eye
adaptive optics systems the FFTS is a crucial component to ensure a
time-stable wavefront correction over the
full aperture of the double-eye telescope, a mandatory pre-requisite
for interferometric observations.
Using a independent HAWAII 1 detector array at a combined focus close
to the science detector, the Fringe
and Flexure Tracking System analyses the complex two-dimensional
interferometric point spread function (PSF)
of a suitably bright reference source at frame rates of up to several
hundred Hertz. By fitting a parameterised
theoretical model PSF to the preprocessed image-data the FFTS
determines the amount of pistonic phase
difference and angular misalignment between the wavefronts of the two
optical paths of LINC-NIRVANA. For
every exposure the corrective parameters are derived in real-time and
transmitted to a dedicated piezo-electric
fast linear mirror for simple path lengths adjustments, and/or to the
adaptive optics systems of the single-eye
telescopes for more complicated corrections.
In this paper we present the basic concept and current status of the
opto-mechanical design of the Fringe and
Flexure Tracker, the operating principle of the fringe and flexure
tracking loops, and the encouraging result of a
laboratory test of the piston control loop.
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