26 July 2016 Status and new developments with the Keck I near-infrared tip-tilt sensor
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The sky coverage and performance of Laser Guide Star (LGS) adaptive optics (AO) systems is limited by the Natural Guide Star (NGS) used for low order correction (tip-tilt and defocus modes). This limitation can be reduced by measuring image motion of the NGS in the near-infrared where it is partially corrected by the LGS AO system and where stars are generally several magnitudes brighter than at visible wavelengths. We have integrated a Near-InfraRed Tip-Tilt Sensor (NIRTTS) with the Keck I telescopes LGS AO system. The sensor is a H2RG-based near-infrared camera with 0.05 arcsecond pixels. Low noise at high sample rates is achieved by only reading a small region of interest, from 2x2 to 16x16 pixels, centered on an NGS anywhere in an 100 arc second diameter field. The sensor operates at either Ks or H-band using light reflected by a choice of dichroic beam-splitters located in front of the OSIRIS integral field spectrograph. The implementation of the NIRTTS involved modifications to the AO bench, real-time control system, higher-level controls and operations software. NIRTTS is nearly ready for science operation in shared-risk mode. We are also implementing a number of enhancements to the NIRTTS system which involve substantial changes to the operations software. This work presents an update of the work performed since the NIRTTS system was reported in Ref. 1 and Ref. 2.
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Bruno Femenía Castellá, Bruno Femenía Castellá, Peter Wizinowich, Peter Wizinowich, Rachel Rampy, Rachel Rampy, Sylvain Cetre, Sylvain Cetre, Scott Lilley, Scott Lilley, Jim Lyke, Jim Lyke, Sam Ragland, Sam Ragland, Paul Stomski, Paul Stomski, Marcos van Dam, Marcos van Dam, "Status and new developments with the Keck I near-infrared tip-tilt sensor", Proc. SPIE 9909, Adaptive Optics Systems V, 990925 (26 July 2016); doi: 10.1117/12.2233173; https://doi.org/10.1117/12.2233173


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