Abstract 117

Submitted by Glen HERRIOT

Authors

G. Herriot, D. Andersen, J. Atwood, C. Boyer, P. Byrnes, R. Conan, B. Ellerbroek, L. Gilles, P. Hickson, K. Jackson, O. Lardière, J.-P. Véran, L. Wang

Affiliations

Herzberg Institute of Astrophysics ; TMT ; U. British Columbia ; U. Victoria

Abstract

NFIRAOS, the TMT Observatory’s initial facility AO system will correct atmospheric turbulence with 50 per cent sky coverage at the galactic pole. It is a multi-conjugate AO system feeding science light from 0.8 to 2.5 microns wavelength to three near-IR client instruments. NFIRAOS is an order 60x60 system with two deformable mirrors optically conjugated to 0 and 12 km. Very low background is an important design driver: one DM is mounted on a tip/tilt platform to reduce surface count; the optics are cooled to -30°C.

NFIRAOS’ real time control uses six sodium laser wavefront sensors and up to three IR natural guide star tip/tilt and/or tip/tilt/focus sensors located within each client instrument. To compensate errors arising from the variability of the sodium layer, to which extremely large telescopes are more sensitive, NFIRAOS uses innovative algorithms coupled with a pair of Truth wavefront sensors that monitors a natural star at low bandwidth.

For calibration, NFIRAOS includes simulators of both natural stars at infinity and laser guide stars at varying range distance. It also includes an IR acquisition camera and a high-speed NGS WFS for operation without lasers.