27 July 2016 Novel tip-tilt sensing strategies for the laser tomography adaptive optics system of the GMT
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Abstract
We investigate the tip-tilt sensor for the laser tomography adaptive optics system of the Giant Magellan Telescope. In the case of the GMTIFS instrument, we require high Strehl over a moderate region of the sky and high throughput with very high sky coverage. In this paper, we simulate the performance of a K-band tip-tilt sensor using an eAPD array. The paper presents a comparison of different centroiding techniques and servo controllers. In addition, we explore the possibility of using the wavefront sensors (WFSs) used in the ground layer adaptive optics (GLAO) mode to supplement the tip-tilt sensor measurement.

The imaging requirement is almost met using the correlation algorithm to estimate the displacement of the spot, along with a high-order controller tailored to the telescope wind shake. This requires a sufficiently bright star to be able to run at 500 Hz, so the sky coverage is limited. In the absence of wind, then the star can be fainter and the requirement is met.

The spectroscopy requirement is met even in the case of high wind. The results are even better if we use the GLAO WFSs as well as the tip-tilt sensors. Further work will explore the viability of inserting a DM in the OIWFS and the resulting tip-tilt performance.
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Marcos A. van Dam, Antonin H. Bouchez, Rodolphe Conan, "Novel tip-tilt sensing strategies for the laser tomography adaptive optics system of the GMT", Proc. SPIE 9909, Adaptive Optics Systems V, 990965 (27 July 2016); doi: 10.1117/12.2231143; https://doi.org/10.1117/12.2231143
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