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"

(in no particular order)
Numbers in the table are approximate or typical. See the references for more details. Please use standard Guidelines in reporting return measurements

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	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 and SPIE'06 paper (Table 1)
Palomar	Richard Dekany, Ed Kibblewhite, Antonin Bouchez	University of Chicago Solid state sum-frequency mode-locked	60-80 ph/s/cm2/W	6-8 W	1.8" FWHM arcsec in 1.0 arcsec V-band seeing	1 ns micropulse inside 300 microsec bursts at 300 Hz repetition rate
Subaru	Masanori Iye, Yutaka Hayano	solid state sum-frequency	To be measured	5.4 W at output of laser	To be measured	~0.8 ns pulses, 143MHz rep rate, mode-locked (quasi-CW) 1.7GHz bandwidth
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: photon return at the primary mirror of the Gemini North telescope, per laser power projected to the sky out of the LLT, with linear polarization (Note: later observed ~30% increase with circular polarization at zenith)	Photon return measurement made in May 2005, during season of lowest sodium abundance, with ~6W projected to the sky (Note: as of May 2009, typical is ~12 W at the ouput of the laser, ~11W projected to the sky, with BTO+LLT throughput ~90%)	1.3 arcsec	0.7 ns pulses, 76 MHz rep rate, CW mode-locked, 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	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	LMCT: Ian Lee; Keck: Sean Adkins; Gemini: Celine d'Orgeville	NSF/AURA for Keck I/Gemini South telescopes resp.	Sum frequency solid state, 1319nm+1064nm into LBO, 0.3 ns pulse every 12 ns (CW mode-locked)	As of Sep. 2009: 40W Keck laser and 50W GS laser demonstrated in the lab, Keck laser passed FAT at LMCT and delivered to WMKO, GS laser pending FAT at LMCT	SPIE article
European Southern Observatory	Domenico Bonaccini Calia, Yan Feng, Luke Taylor	ESO	Frequency-doubled 1178 nm narrow-band Raman fiber amplifier	Demonstrated 50 W cw @ 589 nm	Optics Express paper Frontiers in Optics 2009, postdeadline paper

Interesting Topics

• 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

• CfAO 2006 Fall Retreat Workshop on Laser Technology and Systems for Astronomy Tenaya, Yosemite, CA
• CfAO 2007 Spring Retreat 2nd Laser Workshop. This is tentatively set for some time during spring break March 22 – April 2 and will be held at the UCSC campus.
• CfAO 2007 Fall Retreat 3ed Laser Workshop. Friday November 2, 2007 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2008 Fall Retreat 4th Laser Workshop. Sunday-Monday November 9-10, 2008 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2009 Fall Retreat 5th Laser Workshop. Sunday-Monday November 8-9, 2009 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2010 Fall Retreat 6th Laser Workshop October 31-November 1, 2010 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2011 Fall Retreat 7th Laser Workshop November 9-10, 2011 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2012 Fall Retreat 8th Laser workshop November 4-5, 2012 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2014 Fall Retreat 9th Laser workshop November 16-17, 2014 at the UCLA Conference Center, Lake Arrowhead, CA
• CfAO 2015 Fall Retreat 10th Laser workshop October 23-25, 2015 at the UCLA Conference Center, Lake Arrowhead, CA

Contact

Name	Institution	e-mail
Don Gavel	UC Santa Cruz	gavel@ucolick.org