Overview Science drivers AO Infrastructure at WHT GLAS technicalities Current status of development GLAS: Ground-layer Laser Adaptive optics System

GLAS is only major project on WHT for the next few years Overall top objective: = Increasing sky coverage, approaching 100% = Niche: Integral Field Spectroscopy from μm = Ground-layer correction: not highest Strehl, but scientifically useful correction = Aim for easy operation – keep (relatively) simple Rayleigh option for cost & operational reasons Strategic Considerations

Why on a 4-m telescope ? Big enough to produce exciting science Exploit good seeing on La Palma Prospect of large science programmes Complement large telescopes Cost effective 0.37” Natural seeing NAOMI AO in I band

Sky coverage expectations R = 18 & search field of 2 arcmin diameter Thank-you Remko !

Ground layer turbulence Jimenez & IAC team, 2004

Performance expectations RIJH Uncorrected Corrected PSF specifications using R=17 th mag tip-tilt star (R=18 goal) in median seeing conditions

AO corrects 2D PSF IFS can fully exploit increased resolution Integral field spectroscopy

Multiple band-pass Sources confused Effective spatial resolution is low = Broad band-pass ‘Monochromatic’ data-cube slices Separate star from gas Effective spatial resolution increased Additional spectral separation (Becker et al, astro-ph/ ) Crowded field spectroscopy

Infrastructure

Goal beacon 20 km turbulence laser Laser beacon at fixed distance of 20km, of 200m depth. Laser beam will remain always on-axis. Laser wavelength primarily defined by availability of affordable quality solid-state lasers.

System diagram

The laser Solid state, diode-pumped Yb-YAG ‘disk’ laser Wavelength: 515nm Output power: 30W Beam quality: M 2 < 1.1 Q-switched, 400ns pulse

Laser location

Beam launch telescope

Wavefront sensor shutter

Wavefront sensor 8 x 8 Shack-Hartman Matched to DM 2 arcsec wide apertures Max. elongation 0.2 arcsec

WFS detectors Standard CCD39 for LGS L3CCD for NGS: ~zero read noise gives 1-2 mag advantage LGS loop speed 300 Hz NGS loop speed 100 Hz

Schedule MILESTONEDATE MILESTONEDATE Kick-off meetingApr 2004 Preliminary Design Review Jan 2005 Final Design Review Aug 2005 Lab verification of sub systems May 2006 Science verification Sep 2006 Operation Oct 2006