Field tests of dynamic refocus of Rayleigh laser beacons

James A. Georges, Thomas Stalcup, Roger Angel, Proteep Mallik

Research output: Contribution to journalConference articlepeer-review

7 Scopus citations


Dynamically refocusing the Rayleigh backscatter of a modestly powered laser beacon is a concept for increasing LGS brightness by 10 times1,2,3. Dynamic refocus will allow for high photon return from multiple Rayleigh beacons enabling MCAO for wide field correction of the MMT and Magellan telescopes 2,3,4,5,6. In a system without dynamic refocus, light from a beacon integrated from 20 to 30km is blurred to a length of 14arcsecs. In a system with dynamic refocus, the bow tie is restored to a spot limited only by atmospheric seeing. The dynamic refocus system has been designed to deliver images with <3/4arcsec of induced aberration. This paper reports on field tests performed on the Mt. Bigelow Observatory 61″ telescope, optically configured to appear as an off-axxis sub-aperture of the 6.5m MMT. In these tests the Rayleigh backscatter from pulses of a Q-switched doubled Nd-YAG operating at 5kHZ was dynamically refocused. These preliminary tests present an uncorrected 7 by 3arcsec beacon image. The 7arcsec length is a result of using a field stop as the range-gating mechanism and the 3arcsec limit is due to double pass imaging (projecting and imaging) through the atmosphere in less than ideal seeing conditions. Upon correction, this 7×3arcsec image is dynamically refocused to a 3arcsec FWHM diameter spot.

Original languageEnglish (US)
Pages (from-to)137-148
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 2003
EventAstronomical Adaptive Optics Systems and Applications - San Diego, CA, United States
Duration: Aug 3 2003Aug 4 2003


  • Atmospheric tomography
  • Dynamic refocus
  • Laser guide stars
  • Multi-conjugate adaptive optics
  • Rayleigh beacon

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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