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Open Access Publications from the University of California

Recent Improvements to the Keck II Laser Guide Star Facility


The laser guide star (LGS) adaptive optics (AO) system on the Keck II telescope has been upgraded with a Center Launch Laser System (CLS) and a next generation laser (NGL; i.e. a TOPTICA/MPBC laser) is being implemented. The purpose of the CLS upgrade is to improve the performance of the existing Keck II LGS AO system by reducing the perspective elongation of the LGS as seen by the AO wavefront sensor and hence the measurement error, one of the largest terms in the current error budget. This performance improvement is achieved by projecting the laser from behind the Keck telescope’s secondary mirror instead of from the side of the Keck telescope. The purpose of the NGL upgrade is to increase the laser return and improve laser operability for science operation. The higher return from the NGL would open up new possibilities for further AO upgrades such as a laser asterism to reduce the focal anisoplanatism, and to increase the wavefront sensor (WFS) sampling rate to reduce the bandwidth error in addition to reducing the measurement error.The CLS transitioned to science operation in June 2015. The NGL with the CLS had first light on Dec. 1, 2015 and is being optimized to support transitioning to science operations in April 2016. This paper provides an overview of the design, implementation and on-sky performance of the new launch system and laser. The results are discussed in the context of AO for extremely large telescopes.

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