Keck II Laser Guide Star AO System and Performance with the TOPTICA/MPBC Laser

Creators: Chin, Jason C. Y.; Wizinowich, Peter; Wetherell, Ed; Lilley, Scott; Cetre, Sylvain; Ragland, Sam; Medeiros, Drew; Tsubota, Kevin; Doppmann, Greg; Otarola, Angel; Wei, Kai

Others:: Marchetti, Enrico; Close, Laird M.; Véran, Jean-Pierre

Abstract

The Keck II Laser Guide Star (LGS) Adaptive Optics (AO) System was upgraded from a dye laser to a TOPTICA/MPBC Raman-Fibre Amplification (RFA) laser in December 2015. The W. M. Keck Observatory (WMKO) has been operating its AO system with a LGS for science since 2004 using a first generation 15 W dye laser. Using the latest diode pump laser technology, Raman amplification, and a well-tuned second harmonic generator (SHG), this Next Generation Laser (NGL) is able to produce a highly stable 589 nm laser beam with the required power, wavelength and mode quality. The beam's linear polarization and continuous wave format along with optical back pumping are designed to improve the sodium atom coupling efficiency over previously operated sodium-wavelength lasers. The efficiency and operability of the new laser has also been improved by reducing its required input power and cooling, size, and the manpower to operate and maintain it. The new laser has been implemented on the telescope's elevation ring with its electronics installed on a new Nasmyth sub-platform, with the capacity to support up to three laser systems for future upgrades. The laser is projected from behind the telescope's secondary mirror using the recently implemented center launch system (CLS) to reduce LGS spot size. We will present the new laser system and its performance with respect to power, stability, wavelength, spot size, optical repumping, polarization, efficiency, and its return with respect to pointing alignment to the magnetic field. Preliminary LGSAO performance is presented with the system returning to science operations. We will also provide an update on current and future upgrades at the WMKO.

Additional Information

© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE). The development of the Keck II next generation laser is made possible through the support of the Gordon and Betty Moore Foundation, the W. M. Keck Foundation, the Bob & Renee Parsons Foundation, Friends of W. M. Keck Observatory, and the Thirty Meter Telescope Project. The development of the Keck II center launch facility is made possible in part by the support of the National Science foundation, and the material in this paper describing this facility is based in part upon work supported by the National Science Foundation under Grant No. AST- 0923593. We would like to thank the Thirty Meter Telescope Project for funding Dr. Kai Wei to work on the new Keck II laser facility. We would like to acknowledge the technical contributions of Liz Chock, Randall Campbell, James E. Lyke, Matthias Schoeck and Will Best. We would like to thank the NGL science team of Andrea Ghez, Mike Liu and Claire Max. We would also like to thank the laser teams from TOPTICA AG Photonics, MPBC, and the European Southern Observatory. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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