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Proceedings Paper

Design and testing of a dynamic refocus system for Rayleigh laser beacons
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Paper Abstract

We present the design, laboratory tests and preliminary field tests of a dynamic refocus system for 351nm Rayleigh beacon laser guide stars. The purpose of dynamic refocus is to increase the beacon signal from a pulsed laser, by maintaining focus in a fixed plane while the laser pulse travels through the atmosphere over an extended height range. The focusing element in our system is a moving concave mirror. The optics have been designed and built to focus on a ring of 5 beacons at 1 arc minute radius at the 6.5 m MMT, covering the range 18 through 40 km. Laboratory tests of image quality resulted in 0.5 arcsec refocused images corresponding to the height range 22 through 28 km, free from spherical aberration. Preliminary field tests were performed on the Mt. Bigelow Observatory 1.5 m telescope, with a frequency tripled, Q switched YLF laser beam projected from a 25 cm telescope. To simulate an off axis sub aperture of the MMT, the laser and telescope axes were set 3 m apart and reimaging optics were placed ahead of the refocus unit to image at the same plate scale as the MMT (500 μm/arcsec). Returns from different heights were selected by gating the detector with a Pockels cell. Returns over a 10 km height range from 8km to 18km were brought into focus for a total mirror motion measured to be 900 μm. The system is now ready for testing dynamic refocus, which will be accomplished by attaching the mirror to a metal resonator tuned to the laser pulse frequency. The range from 23 to 35 km to be used will require a motion of 500 μm.

Paper Details

Date Published: 7 February 2003
PDF: 11 pages
Proc. SPIE 4839, Adaptive Optical System Technologies II, (7 February 2003); doi: 10.1117/12.459354
Show Author Affiliations
James A. Georges, Steward Observatory/Univ. of Arizona (United States)
Proteep Mallik, Steward Observatory/Univ. of Arizona (United States)
Thomas Stalcup, Steward Observatory/Univ. of Arizona (United States)
James Roger P. Angel, Steward Observatory/Univ. of Arizona (United States)
Roland J. Sarlot, Steward Observatory/Univ. of Arizona (United States)


Published in SPIE Proceedings Vol. 4839:
Adaptive Optical System Technologies II
Peter L. Wizinowich; Domenico Bonaccini, Editor(s)

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