Optimal LGS pointing with faint tip-tilt NGS

Richard Dekany

doi:10.1117/12.857841

28 July 2010 Optimal LGS pointing with faint tip-tilt NGS

Richard Dekany

Proceedings Volume 7736, Adaptive Optics Systems II; 773625 (2010) https://doi.org/10.1117/12.857841
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

Experience with the current generation of astronomical single laser guide star (LGS) adaptive optics (AO) systems has demonstrated system performance that is often limited by residual tip-tilt errors induced by the paucity of bright tip-tilt natural guide stars (NGS). To overcome this limitation, we are developing a new generation of tip-tilt sensors that will operate at near-infrared wavelengths where the NGS is sharpened to the diffraction limit. To optimize performance, single LGS AO systems utilizing sharpened tip-tilt NGS should generally not point their LGS directly toward their science target. Rather, optimal performance for wide sky coverage is obtained by offsetting LGS pointing along a radius connecting the science target and the tip-tilt NGS. We demonstrate that determination of the jointly optimized LGS pointing angle and tip-tilt wavefront sensor (WFS) integration time can improve performance metrics by factors of several, particularly for faintest NGS operation. We find the LGS offset should be as much as 1/2 the distance to the NGS to maximize Strehl ratio at near-infrared wavelengths and ≈ 1/4 the distance to the NGS to maximize ensquared energy, with lesser off-pointing for brighter NGS. Future AO systems may benefit from predictive determination of optimal LGS offsetting, based upon changing atmospheric conditions and observational geometries.

Citation Download Citation

Richard Dekany "Optimal LGS pointing with faint tip-tilt NGS", Proc. SPIE 7736, Adaptive Optics Systems II, 773625 (28 July 2010); https://doi.org/10.1117/12.857841

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