干旱区生态环境知识资源中心

GLAS is an upgrade of the William Herschel Telescope's existing natural-guide-star (NGS) AO system NAOMI to incorporate a 20-W Rayleigh laser guide star (LGS) projected to an altitude of 1-5 kin. It is currently being commissioned on-sky, and we review here the current status of the project. GLAS/NAOMI delivers dramatic improvements in PSF in both the near-IR. (AO-corrected FWHM close to the diffraction limit, >similar to 0.15 arcsec) and in the optical (factor of similar to 2 reduction in FWHM). The performance is similar to that with NOS, and is consistent with predictions from modelling. The main advantage over NOS AO is the large gain in sky coverage (from similar to 1% to similar to 100% at galactic latitude 40 degrees). GLAS provides the first on-sky demonstration of closed-loop ground-layer AO (GLAO), and is the first Rayleigh LGS AO system to be offered for general use. at any telescope.