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Title: Desing of a Laser Guide Star System for the Keck II Telescope

Abstract

A laser guide star system similar to that deployed at the Lick Observatory has been designed for the Keck II 10 m telescope on Mauna Kea, Hawaii. The subaperature size on the primary is comparable to that at Lick, and at the same observational wavelength centered about the K band, so that the average power requirements of the laser system are also comparable, at about 20 W. One major difference is that the seeing at Mauna Kea is about a factor of two better than at Lick so that the spot diameter requirements are smaller and this can give rise to reduced back scatter resulting from saturation effects in the sodium layer. To reduce the peak flux in the sodium layer and obtain a smaller spot diameter, the output beam diameter has been increased along with the repetition rate of the laser. As with the Lick laser system, a dye laser is pumped by a series of frequency doubled YAG lasers which are remotely located and coupled to the dye laser on the telescope by optical fibers. The laser system has a full set of beam control optics as well as launch telescope and safety systems. A computer system couplesmore » the laser system to the User Interface and Supervisory Control system of the main telescope. The laser system is due to be shipped to Keck during the fall of 1997 where it will be integrated with the telescope at Mauna Kea. The Adaptive Optics and Optics Bench systems will be integrated first and be ready for integration with the laser in the summer of 1998. 1 ref., 8 figs.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
600576
Report Number(s):
UCRL-JC-128570; CONF-9706204-
ON: DE98051379
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Laser Guide Star Workshop, Garching bei Munich (Germany), 22-27 Jun 1997; Other Information: PBD: 11 Sep 1997
Country of Publication:
United States
Language:
English
Subject:
44 INSTRUMENTATION, INCLUDING NUCLEAR AND PARTICLE DETECTORS; OPTICAL SYSTEMS; LIGHT SOURCES; CONTROL SYSTEMS; DESIGN; TELESCOPES; FOCUSING

Citation Formats

Friedman, H.W., Erbert, G.V., Kuklo, T., Thompson, G.R., Wong, N.J., Gavel, D.T., Salmon, J.T., and Feldman, M. Desing of a Laser Guide Star System for the Keck II Telescope. United States: N. p., 1997. Web.
Friedman, H.W., Erbert, G.V., Kuklo, T., Thompson, G.R., Wong, N.J., Gavel, D.T., Salmon, J.T., & Feldman, M. Desing of a Laser Guide Star System for the Keck II Telescope. United States.
Friedman, H.W., Erbert, G.V., Kuklo, T., Thompson, G.R., Wong, N.J., Gavel, D.T., Salmon, J.T., and Feldman, M. 1997. "Desing of a Laser Guide Star System for the Keck II Telescope". United States. doi:.
@article{osti_600576,
title = {Desing of a Laser Guide Star System for the Keck II Telescope},
author = {Friedman, H.W. and Erbert, G.V. and Kuklo, T. and Thompson, G.R. and Wong, N.J. and Gavel, D.T. and Salmon, J.T. and Feldman, M.},
abstractNote = {A laser guide star system similar to that deployed at the Lick Observatory has been designed for the Keck II 10 m telescope on Mauna Kea, Hawaii. The subaperature size on the primary is comparable to that at Lick, and at the same observational wavelength centered about the K band, so that the average power requirements of the laser system are also comparable, at about 20 W. One major difference is that the seeing at Mauna Kea is about a factor of two better than at Lick so that the spot diameter requirements are smaller and this can give rise to reduced back scatter resulting from saturation effects in the sodium layer. To reduce the peak flux in the sodium layer and obtain a smaller spot diameter, the output beam diameter has been increased along with the repetition rate of the laser. As with the Lick laser system, a dye laser is pumped by a series of frequency doubled YAG lasers which are remotely located and coupled to the dye laser on the telescope by optical fibers. The laser system has a full set of beam control optics as well as launch telescope and safety systems. A computer system couples the laser system to the User Interface and Supervisory Control system of the main telescope. The laser system is due to be shipped to Keck during the fall of 1997 where it will be integrated with the telescope at Mauna Kea. The Adaptive Optics and Optics Bench systems will be integrated first and be ready for integration with the laser in the summer of 1998. 1 ref., 8 figs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1997,
month = 9
}

Conference:
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  • A laser system to generate sodium-layer guide stars has been designed, built and delivered to the Keck Observatory in Hawaii. The system uses frequency doubled YAG lasers to pump liquid dye lasers and produces 20 W of average power. The design and performance results of this laser system are presented.
  • The Laser Guide Star (LGS) system for the Keck II, 10 m telescope consists of two separate but interconnected systems, the laser and the adaptive optics bench. The laser portion of the LGSl is a set of five frequency doubled YAG lasers pumping a master oscillator-power amplifier dye chain to produce up to 30 W of 589 p at 26 kHz of tuned light. Presently the laser system has been set up at the Keck facility in Waimea, HI and is undergoing test and evaluation. When it will be set up on the Keck II telescope, the pump lasers, dyemore » master oscillator and associated control equipment will be located on the dome floor and the dye laser amplifiers, beam control system and diagnostics will be mounted directly on the telescope as shown in Fig. 1, Extensive use of fiber optics for both transmission of the oscillator pulse and the pump laser light has been used.« less
  • The design, installation and performance data of a 20 W pulsed laser system for the 3 meter Shane telescope at the Lick Observatory is presented.
  • The Keck telescope adaptive optics system is designed to optimize performance in he 1 to 3 micron region of observation wavelengths (J, H, and K astronomical bands). The system uses a 249 degree of freedom deformable mirror, so that the interactuator spacing is 56 cm as mapped onto the 10 meter aperture. 56 cm is roughly equal to r0 at 1.4 microns, which implies the wavefront fitting error is 0.52 ({lambda}/2{pi})({ital d}/{ital r}{sub 0}){sup 5/6} = 118 nm rms. This is sufficient to produce a system Strehl of 0.74 at 1.4 microns if all other sources of error are negligible,more » which would be the case with a bright natural guidestar and very high control bandwidth. Other errors associated with the adaptive optics will however contribute to Strehl degradation, namely, servo bandwidth error due to inability to reject all temporal frequencies of the aberrated wavefront, wavefront measurement error due to finite signal-to-noise ratio in the wavefront sensor, and, in the case of a laser guidestar, the so-called cone effect where rays from the guidestar beacon fail to sample some of the upper atmosphere turbulence. Cone effect is mitigated considerably by the use of the very high altitude sodium laser guidestar (90 km altitude), as opposed to Rayleigh beacons at 20 km. However, considering the Keck telescope`s large aperture, this is still the dominating wavefront error contributor in the current adaptive optics system design.« less
  • The 349 degree of freedom Keck adaptive optics system will be mapped on to the 36 segment Keck primary mirror. Each telescope segment is independently controlled in piston and tilt by an active control system and each segment also has its own set of aberrations. This presents a unique set of problems for the Keck adaptive optics system, not encountered with continuous primaries. To a certain extent the low order segment aberrations, beginning with focus, can be corrected statically by the adaptive optic system. However, the discontinuous surface at the segment edges present special problems in sensing and correcting wavefrontmore » with laser guide stars or natural guide stars.« less