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r20 - 21 Apr 2008 - 22:00:52 - DavidLMYou are here: TWiki >  CfAO Web  > SodiumLaserGuidestars

Sodium Laser Guidestar Page

Sodium wavelength lasers are critical to the next generation of adaptive optics for ground-based astronomical telescopes. Important issues are:

  • Understanding the physics of the sodium layer / laser photon interaction in order to optimize the usable wavefront reference return signal
  • Considerations of cost, size, and power consumption in order to make it feasible to field such lasers at mountaintop astronomical observatories
  • Controlling Rayleigh backscatter and "fratricide" which is a noise source to the wavefront sensing
  • Obtaining high laser wavefront quality and engineering the laser projection system to form the smallest possible guide star spot on the sodium layer

Summary of Sodium Laser Guide Stars now "On-the-Sky" - Please use standard Guidelines in reporting return measurements

(in no particular order)
Numbers in the table are approximate or typical. See the references for more details.

Facility Principal Investigators Laser Maker and Type Return / Watt (Details) Average Power Spot Size (apparent) Pulse & Spectral Format Web Link
Lick Mt. Hamilton Claire Max, Don Gavel LLNL Tunable Dye 10 ph/s/cm2/W 12 W 2 arcsec 100 ns, 11 kHz, 2 GHz EO modulated LGS project at LLNL and instrumentation pages at Lick and SPIE paper
Starfire Optical Range Bob Fugate, Craig Denman SOR Solid state, resonant sum-frequency generator 100 ph/s/cm2/W seasonal average 50 W seeing limited 1.4-3 arcsec (site has r0=7.8cm avg) CW 10 kHz line SPIE article and Craig Denman's talk at the Nov 2006 LaserWorkshop
W. M. Keck Observatory Peter Wizinowich LLNL Tunable Dye 10 ph/s/cm2/W 12-15 W 1.8" x 2.3" (average stacked) 100 ns, 25 kHz, 2 GHz EO modulated K2LGSAO web, LGS Photometry and SPIE'06 paper (Table 1)
Palomar Richard Dekany, Ed Kibblewhite University of Chicago Solid state sum-frequency mode-locked 30-130 ph/s/cm2/W 6-8 W as good as 2.3 FWHM arcsec in 1.0 arcsec V-band seeing @ 5.5 W power 1 ns micropulse inside 300 microsec bursts at 300 Hz repetition rate instrumentation page at COO and note on guide star return flux
Subaru Masanori Iye, Yutaka Hayano solid state sum-frequency ? 4.7 W ? ? press release
Gemini North Francois Rigaut, Celine D'Orgeville Lockheed-Martin Coherent Technologies diode-pumped solid state 1.06+1.32micron sum-frequency laser 27photons/cm^2/s/W (laser power projected to the sky, i.e. out of the LLT) with linear polarization (~30% increase with circular polarization) ~12 W at the ouput of the laser, ~9W projected to the sky; measurement made in May 2005, during season of lowest sodium abundance 1.3 arcsec 0.7 ns pulses, 76 MHz rep rate, mode-locked (quasi-CW), 550MHz bandwidth Altair LGS instrument page and laser commissioning news
Very Large Telescope Domenico Bonaccini Calia Max Planck Institutes Tunable Dye 54 ph/s/cm2/W 10 W 1.25 arcsec CW 3x10 MHz separated by 110MHz press release from VLT, laser specs from MPIE, SPIE article on first light

New Laser Development

Institution Principal Investigators Sponsor Laser Type Progress Reference
Lockheed-Martin Coherent Technologies Allen Tracy, Allen Hankla AODP Sum frequency solid state, 1319nm+1064nm into PPSLT, modular pulse format 1.5 W / 10 W goal SPIE article
Lawrence Livermore National Laboratory Dee Pennington, Jay Dawson AODP and CfAO Sum frequency fiber, 1583nm+938nm into PPSLT, modular pulse format, 500 MHz linewidth 3.5 W / 5-10 W goal SPIE article
Lockheed-Martin Coherent Technologies Allen Hankla Keck I and Gemini South Telescopes Sum frequency solid state, 1319nm+1064nm into LBO, 0.7 nm pulse every 12 ns quasi CW 20W Keck laser demonstrated in the lab, >40W of 589nm demonstrated in the lab for GS laser (October 2007) SPIE article

Interesting Topics

Discuss these in the blogs below

  • Measurements and comparisons
    • Photometric method and designation of laser return (e.g. photons/sec/cm^2/Watt compared to that of a spectrophotometric star through a narrow band filter referred to the top of the telescope)
    • Laser beam quality (e.g. M^2, apparent FWHM on the sky)
    • Laser output power (e.g. power measured at the output of the laser, power measured or inferred at the output of the launch telescope, is all the power is at the D2 line?, etc.)
    • Methods of independently determining sodium column density (e.g. atoms/m^2)
  • Crucial component development
    • Sum-frequency power crystals – technology advancement, consortium runs, etc.
    • Fibers for high power beam transport to launch telescope – e.g. photonic crystal fibers at Subaru and VLT

Meetings

Contacts List

Name Institution e-mail
Richard Dekany Caltech Optical Observatories rgd@astro.caltech.edu
Don Gavel UC Santa Cruz gavel@ucolick.org
Ed Kibblewhite University of Chicago edk@oddjob.uchicago.edu
Renu Tripathi Caltech Optical Observatories renu@caltech.edu

Blogs

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pptpps CfAO_Retreat_March_2007.pps manage 8910.5 K 26 Mar 2007 - 17:15 DomenicoBonacciniCalia ESO LGSF status March 2007
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