NFIRAOS — Multiconjugate AO System for TMT
Glen Herriot#, David Andersen#, Jenny Atwood#, Peter Byrnes#, Corinne Boyer*, Kris Caputa#, Carlos Correia#, Jennifer Dunn#, Brent Ellerbroek*, Joeleff Fitzsimmons#, Luc Gilles*, Paul Hickson$, Alexis Hill#, John Pazder#, Vlad Reshetov, Malcolm Smith#, Jean-Pierre Véran#, Lianqi Wang* , Ivan Wevers#
#NRC-HIA 5071 West Saanich Rd, Victoria, Canada. . *TMT 1111 S. Arroyo, Pasadena CA. $UBC 6224 Agricultural Road, Vancouver, Canada
NFIRAOS, the Adaptive Optics system for the Thirty Meter Telescope, is a Multiconjugate Adaptive Optics System of order 60x60 with two deformable mirrors and six laser guide star wavefront sensors. NFIRAOS is 8 x 10 x 5 m (L x W x H) on a Nasmyth Platform and supports three client instruments operating over 0.8 – 2.5 µm wavelength range. In this paper we discuss: NFIRAOS’ requirements and architecture; changes to NFIRAOS since the last AO4ELT conference; interior details of NFIRAOS; interfaces to instruments; integration and verification plans. Top-level science requirements include 50% sky coverage at the galactic pole with <187 nm wavefront error. Astrometry is an important science driver – to minimize image distortion, we have recently revised the optical design to use four off-axis paraboloidal mirrors. We have vastly simplified the laser WFS zoom optics and moved them inside the cold enclosure. To control image magnification, differential magnification and tip/tilt/focus, NFIRAOS’ client instruments have three low-order warfront sensors monitoring near-infrared natural guide stars. These stars are sharpened by NFIRAOS, which assists sky coverage. NFIRAOS will have high throughput and low thermal background – it will be cooled to -30 °C. The insulated walls have a buried cold plate to intercept heat leakage and isothermalize the interior of NFIRAOS. Instruments have stringent requirements on heat leakage and must provide their own rotator and interface to NFIRAOS, including a rotating seal. For wavelength and flat field calibration of client instruments, a NFIRAOS Science Calibration Unit (NSCU) feeds light in the entrance window, through NFIRAOS, to instruments. Inside NFIRAOS are deployable light sources simulating natural and laser guide stars, a focal plane mask with pinholes illuminated by the NSCU, as well as a turbulence phase screen. A prototype screen has been manufactured by magneto-rheological machining. We are currently updating the NFIRAOS preliminary design.