Lasers for the Next-Generation
Adaptive Optics System
for the Keck Observatory
on behalf of the NGAO concept study group
Claire Max, Peter Wizinowich,
Rich Dekany, Mike Liu
and participants from the Keck, Palomar, and
CfAO Spring Retreat, 2007
UC Santa Cruz
Keck Next-Generation Adaptive Optics (NGAO) is
designed to provide powerful new capabilities
1. Near diffraction-limited in the near-IR (Strehl >80%)
• A PSF with unprecedented precision, stability and contrast.
2. Vastly increased sky coverage and multiplexing
• Enables a much broader range of science programs.
3. AO correction at red optical wavelengths (0.6-1.0um)
• Highest angular resolution of any filled-aperture telscope.
Gavel: NGAO at Keck CfAO Spring Retreat, 2007 2
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
Gavel: NGAO at Keck CfAO Spring Retreat, 2007 3
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?
Gavel: NGAO at Keck CfAO Spring Retreat, 2007 4
Very important additional considerations
• Cost to operate and maintain
• Size, weight, and power
Gavel: NGAO at Keck CfAO Spring Retreat, 2007 5