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Proceedings Paper

The fringe detection laser metrology for the GRAVITY interferometer at the VLTI
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Paper Abstract

Interferometric measurements of optical path length differences of stars over large baselines can deliver extremely accurate astrometric data. The interferometer GRAVITY will simultaneously measure two objects in the field of view of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) and determine their angular separation to a precision of 10 μas in only 5 minutes. To perform the astrometric measurement with such a high accuracy, the differential path length through the VLTI and the instrument has to be measured (and tracked since Earth's rotation will permanently change it) by a laser metrology to an even higher level of accuracy (corresponding to 1 nm in 3 minutes). Usually, heterodyne differential path techniques are used for nanometer precision measurements, but with these methods it is difficult to track the full beam size and to follow the light path up to the primary mirror of the telescope. Here, we present the preliminary design of a differential path metrology system, developed within the GRAVITY project. It measures the instrumental differential path over the full pupil size and up to the entrance pupil location. The differential phase is measured by detecting the laser fringe pattern both on the telescopes' secondary mirrors as well as after reflection at the primary mirror. Based on our proposed design we evaluate the phase measurement accuracy based on a full budget of possible statistical and systematic errors. We show that this metrology design fulfills the high precision requirement of GRAVITY.

Paper Details

Date Published: 22 July 2010
PDF: 18 pages
Proc. SPIE 7734, Optical and Infrared Interferometry II, 773421 (22 July 2010); doi: 10.1117/12.856698
Show Author Affiliations
H. Bartko, Max-Planck-Institut für extraterrestrische Physik (Germany)
S. Gillessen, Max-Planck-Institut für extraterrestrische Physik (Germany)
S. Rabien, Max-Planck-Institut für extraterrestrische Physik (Germany)
M. Thiel, Max-Planck-Institut für extraterrestrische Physik (Germany)
A. Gräter, Max-Planck-Institut für extraterrestrische Physik (Germany)
M. Haug, Max-Planck-Institut für extraterrestrische Physik (Germany)
S. Kellner, Max-Planck-Institut für extraterrestrische Physik (Germany)
F. Eisenhauer, Max-Planck-Institut für extraterrestrische Physik (Germany)
S. Lacour, LESIA, Observatoire de Paris, CNRS, UPMC, Univ. Paris Diderot (France)
C. Straubmeier, Univ. zu Köln (Germany)
J.-P. Berger, Lab. d'Astrophysique de l'Observatoire de Grenoble (France)
European Southern Observatory (Germany)
L. Jocou, Lab. d'Astrophysique de l'Observatoire de Grenoble (France)
W. Chibani, Max-Planck-Institut für extraterrestrische Physik (Germany)
S. Lüst, Max-Planck-Institut für extraterrestrische Physik (Germany)
D. Moch, Max-Planck-Institut für extraterrestrische Physik (Germany)
O. Pfuhl, Max-Planck-Institut für extraterrestrische Physik (Germany)
W. Fabian, Max-Planck-Institut für extraterrestrische Physik (Germany)
C. Araujo-Hauck, Univ. zu Köln (Germany)
K. Perraut, Lab. d'Astrophysique de l'Observatoire de Grenoble (France)
W. Brandner, Max-Planck-Institut für Astronomie (Germany)
G. Perrin, LESIA, Observatoire de Paris, CNRS, UPMC, Univ. Paris Diderot (France)
A. Amorim, Univ. de Lisboa (Portugal)


Published in SPIE Proceedings Vol. 7734:
Optical and Infrared Interferometry II
William C. Danchi; Françoise Delplancke; Jayadev K. Rajagopal, Editor(s)

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