Lasers for the NextGeneration Adaptive Optics System for the Keck Observatory

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Lasers for the Next-Generation Adaptive Optics
System for the Keck Observatory

• Donald Gavel
• on behalf of the NGAO concept study group
• Claire Max, Peter Wizinowich,
• Rich Dekany, Mike Liu
• and participants from the Keck, Palomar, and
  UCO/Lick Observatories

CfAO Spring Retreat, 2007 UC Santa Cruz
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Keck Next-Generation Adaptive Optics (NGAO) is
designed to provide powerful new capabilities

• Near diffraction-limited in the near-IR (Strehl
  gt80)
• A PSF with unprecedented precision, stability and
  contrast.
• Vastly increased sky coverage and multiplexing
• Enables a much broader range of science programs.
• AO correction at red optical wavelengths
  (0.6-1.0um)
• Highest angular resolution of any filled-aperture
  telscope.

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Laser Guidestar Concepts for NGAO

• Multi-laser guidestar tomography
• Counter the cone effect
• Wide contiguous field and multi-object AO
• Variable configuration
• Compact constellation for high on-axis Strehl
• Wider constellation for wider field correction
  and MOAO
• Point some LGS at tip/tilt stars

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Ongoing trade studies

• Rayleigh fratricide do we need a pulsed laser?
• Beam transport can we use a fiber?
• Return vs pulse format and bandwidth should we
  require narrow band? Can we do pulse tracking?
• Number of LGS, and constellation configuration
  currently indicating 5 to 9 LGS in 30 to 240
  arcsec diameter variable constellations
• Wavefront error as a function of laser power
  how much total power? How much margin is needed
  to cover throughput, seeing, and Na density
  fluctuations?

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Very important additional considerations

• Reliability
• Cost
• Cost to operate and maintain
• Size, weight, and power