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28 July 2008 Fringe tracking optimization with 4 beams: application to GRAVITY
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Abstract
GRAVITY, a VLTI second generation instrument, requires a fringe tracker combining four beams. Its design is driven by the observation of the Galactic Center and implies stringent fringe sensor specifications. We present the simulations of the fringe tracking closed-loop performance with an optical path difference (OPD) turbulence spectrum using a Kolmogorov model of the atmosphere for typical seeing conditions at VLTI (r0 = 0.95 m, t0 = 47 ms at 2.2 μm). We show that the total residual OPD standard deviation can be as low as λ/12 at a sampling frequency of 350 Hz on a guide star with a magnitude of mK = 10. To obtain this performance, we compared several 4-beam pairwise co-axial combination conceptual architectures and show that the optimal 4-beam combination is the one measuring the OPD on the six baselines.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
K. Houairi, F. Cassaing, G. Perrin, F. Eisenhauer, W. Brandner, C. Straubmeier, and S. Gillessen "Fringe tracking optimization with 4 beams: application to GRAVITY", Proc. SPIE 7013, Optical and Infrared Interferometry, 70131B (28 July 2008); https://doi.org/10.1117/12.790967
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