GRAVITY: the impact of non-common optical paths within the metrology system

Yitping Kok; Stefan Gillessen; Sylvestre Lacour; Frank Eisenhauer; Nicolas Blind; Johannes Weber; Magdalena Lippa; Oliver Pfuhl; Leonard Burtscher; Ekkehard Wieprecht; Thomas Ott; Marcus Haug; Stefan Kellner; Frank Haussmann; Eckhard Sturm; Annemieke Janssen; Reinhard Genzel; Guy Perrin; Karine Perraut; Christian Straubmeier; Wolfgang Brandner; Antonio Amorim; Oliver Hans

doi:10.1117/12.2055567

24 July 2014 GRAVITY: the impact of non-common optical paths within the metrology system

Yitping Kok, Stefan Gillessen, Sylvestre Lacour, Frank Eisenhauer, Nicolas Blind, Johannes Weber, Magdalena Lippa, Oliver Pfuhl, Leonard Burtscher, Ekkehard Wieprecht, Thomas Ott, Marcus Haug, Stefan Kellner, Frank Haussmann, Eckhard Sturm, Annemieke Janssen, Reinhard Genzel, Guy Perrin, Karine Perraut, Christian Straubmeier, Wolfgang Brandner, Antonio Amorim, Oliver Hans

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Proceedings Volume 9146, Optical and Infrared Interferometry IV; 914625 (2014) https://doi.org/10.1117/12.2055567
Event: SPIE Astronomical Telescopes + Instrumentation, 2014, Montréal, Quebec, Canada

Abstract

The laser metrology system in the GRAVITY instrument plays a crucial role in an attempt at high-precision narrow-angle astrometry. With a design goal of achieving 10 microarcseconds precision in astrometry, the system must measure the optical path difference between two beam combiners within GRAVITY to an accuracy of better than 5nm. However in its current design, some parts of the optical paths of the metrology system are not common to the optical paths of starlight (the science path) which it must measure with high accuracy. This state of the design is true for most but not all the baselines which will be used by the GRAVITY instrument. The additional non-common optical paths could produce inaccurate path length measurements and consequently inaccurate measurements of the differential phase between fringe packets of two nearby celestial objects, which is the main astrometric observable of the instrument. With reference to the stability and the sensitivity of the non-common paths, this paper describes the impact of a biased differential phase measurement on the narrowangle astrometry and the image reconstruction performance of the GRAVITY instrument. Several alternative designs are also discussed.

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Yitping Kok, Stefan Gillessen, Sylvestre Lacour, Frank Eisenhauer, Nicolas Blind, Johannes Weber, Magdalena Lippa, Oliver Pfuhl, Leonard Burtscher, Ekkehard Wieprecht, Thomas Ott, Marcus Haug, Stefan Kellner, Frank Haussmann, Eckhard Sturm, Annemieke Janssen, Reinhard Genzel, Guy Perrin, Karine Perraut, Christian Straubmeier, Wolfgang Brandner, Antonio Amorim, and Oliver Hans "GRAVITY: the impact of non-common optical paths within the metrology system", Proc. SPIE 9146, Optical and Infrared Interferometry IV, 914625 (24 July 2014); https://doi.org/10.1117/12.2055567

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