The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Performance Characterization

The Keck II Telescope is the first 8-10 m class telescope equipped with a laser guide star adaptive optics (LGS AO) system. Under normal seeing conditions, the LGS AO system produces K-band Strehl ratios between 30% and 40% using bright tip-tilt guide stars, and it works well with tip-tilt guide stars as faint as m_R=18, with partial correction for stars up to a magnitude fainter. This paper presents the algorithms implemented in the LGS AO system, as well as experimental performance results. A detailed error budget shows excellent agreement between the measured and expected image quality for both bright and faint guide stars.