24 July 2014 GRAVITY: the impact of non-common optical paths within the metrology system
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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.
© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Yitping Kok, Yitping Kok, Stefan Gillessen, Stefan Gillessen, Sylvestre Lacour, Sylvestre Lacour, Frank Eisenhauer, Frank Eisenhauer, Nicolas Blind, Nicolas Blind, Johannes Weber, Johannes Weber, Magdalena Lippa, Magdalena Lippa, Oliver Pfuhl, Oliver Pfuhl, Leonard Burtscher, Leonard Burtscher, Ekkehard Wieprecht, Ekkehard Wieprecht, Thomas Ott, Thomas Ott, Marcus Haug, Marcus Haug, Stefan Kellner, Stefan Kellner, Frank Haussmann, Frank Haussmann, Eckhard Sturm, Eckhard Sturm, Annemieke Janssen, Annemieke Janssen, Reinhard Genzel, Reinhard Genzel, Guy Perrin, Guy Perrin, Karine Perraut, Karine Perraut, Christian Straubmeier, Christian Straubmeier, Wolfgang Brandner, Wolfgang Brandner, Antonio Amorim, Antonio Amorim, Oliver Hans, 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); doi: 10.1117/12.2055567; https://doi.org/10.1117/12.2055567
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