The GRAVITY metrology system: narrow-angle astrometry via phase-shifting interferometry

Magdalena Lippa; Nicolas Blind; Stefan Gillessen; Yitping Kok; Johannes Weber; Frank Eisenhauer; Oliver Pfuhl; Annemieke Janssen; Marcus Haug; Frank Haußmann; Stefan Kellner; Oliver Hans; Ekkehard Wieprecht; Thomas Ott; Leonard Burtscher; Reinhard Genzel; Eckhard Sturm; Reiner Hofmann; S. Huber; David Huber; Stefanie Senftleben; Andreas Pflüger; Roland Greßmann; Guy Perrin; Karine Perraut; Wolfgang Brandner; Christian Straubmeier; Antonio Amorim; Markus Schöller

doi:10.1117/12.2054637

24 July 2014 The GRAVITY metrology system: narrow-angle astrometry via phase-shifting interferometry

Magdalena Lippa, Nicolas Blind, Stefan Gillessen, Yitping Kok, Johannes Weber, Frank Eisenhauer, Oliver Pfuhl, Annemieke Janssen, Marcus Haug, Frank Haußmann, Stefan Kellner, Oliver Hans, Ekkehard Wieprecht, Thomas Ott, Leonard Burtscher, Reinhard Genzel, Eckhard Sturm, Reiner Hofmann, S. Huber, David Huber, Stefanie Senftleben, Andreas Pflüger, Roland Greßmann, Guy Perrin, Karine Perraut, Wolfgang Brandner, Christian Straubmeier, Antonio Amorim, Markus Schöller

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Proceedings Volume 9146, Optical and Infrared Interferometry IV; 914622 (2014) https://doi.org/10.1117/12.2054637
Event: SPIE Astronomical Telescopes + Instrumentation, 2014, Montréal, Quebec, Canada

Abstract

The VLTI instrument GRAVITY will provide very powerful astrometry by combining the light from four tele- scopes for two objects simultaneously. It will measure the angular separation between the two astronomical objects to a precision of 10 μas. This corresponds to a differential optical path difference (dOPD) between the targets of few nanometers and the paths within the interferometer have to be maintained stable to that level. For this purpose, the novel metrology system of GRAVITY will monitor the internal dOPDs by means of phase- shifting interferometry. We present the four-step phase-shifting concept of the metrology with emphasis on the method used for calibrating the phase shifts. The latter is based on a phase-step insensitive algorithm which unambiguously extracts phases in contrast to other methods that are strongly limited by non-linearities of the phase-shifting device. The main constraint of this algorithm is to introduce a robust ellipse fitting routine. Via this approach we are able to measure phase shifts in the laboratory with a typical accuracy of λ=2000 or 1 nm of the metrology wavelength.

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Magdalena Lippa, Nicolas Blind, Stefan Gillessen, Yitping Kok, Johannes Weber, Frank Eisenhauer, Oliver Pfuhl, Annemieke Janssen, Marcus Haug, Frank Haußmann, Stefan Kellner, Oliver Hans, Ekkehard Wieprecht, Thomas Ott, Leonard Burtscher, Reinhard Genzel, Eckhard Sturm, Reiner Hofmann, S. Huber, David Huber, Stefanie Senftleben, Andreas Pflüger, Roland Greßmann, Guy Perrin, Karine Perraut, Wolfgang Brandner, Christian Straubmeier, Antonio Amorim, and Markus Schöller "The GRAVITY metrology system: narrow-angle astrometry via phase-shifting interferometry", Proc. SPIE 9146, Optical and Infrared Interferometry IV, 914622 (24 July 2014); https://doi.org/10.1117/12.2054637

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