NFIRAOS: TMT's facility adaptive optics system

Abstract

NFIRAOS, the TMT Observatory's initial facility AO system is a multi-conjugate AO system feeding science light from 0.8 to 2.5 microns wavelength to several near-IR client instruments. NFIRAOS has two deformable mirrors optically conjugated to 0 and 11.2 km, and will correct atmospheric turbulence with 50 per cent sky coverage at the galactic pole. An important requirement is to have very low background: the plan is to cool the optics; and one DM is on a tip/tilt stage to reduce surface count. NFIRAOS' real time control uses multiple 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. Extremely large telescopes are sensitive to errors due to the variability of the sodium layer. To reduce this sensitivity, NFIRAOS uses innovative algorithms coupled with Truth wavefront sensors to monitor a natural star at low bandwidth. It also includes an IR acquisition camera, and a high speed NGS WFS for operation without lasers. For calibration, NFIRAOS includes simulators of both natural stars at infinity and laser guide stars at varying range distance. Because astrometry is an important science programme for NFIRAOS, there is a precision pinhole mask deployable at the input focal plane. This mask is illuminated by a science wavelength and flat-field calibrator that shines light into NFIRAOS' entrance window. We report on recent effort especially including trade studies to reduce field distortion in the science path and to reduce cost and complexity.

First light adaptive optics systems and components for the Thirty Meter Telescope

“…Several additional benefits are now apparent after the four-OAP design has been developed, including (i) smaller non-common path aberrations in the LGS WFS optical path, and (ii) simpler implementation of the turbulence generator and guide star source simulator optics. These design features, and other improvements to the NFIRAOS optomechanical design, are described in a separate paper 12 . Table 5 lists the fundamental AO performance requirements for component to be integrated into NFIRAOS and the LGSF.…”

“…Finally, work continues to assess and optimize the overall performance of the full system through a combination of modeling, lab experiments, and field measurements. Further information on these topics is given below, and in other papers from this meeting [12][13][14][15][16][17][18][19][20][21][22] and prior publications [23][24][25][26][27] .…”

High fidelity optical modeling for the TMT

“…The specific implementation of the MAOS software for TMT is used in connection with the Narrow Field InfraRed Adaptive Optics System (NFIRAOS). NFIRAOS is the early-light AO system for TMT 13,14 and is a multi-conjugate AO system (MCAO) that will utilize 6 laser guide-stars and two deformable mirrors to provide diffraction-limited atmospheric turbulence compensation at near IR wavelengths over a 10"-30" FoV. A fully functional simulation of the NFIRAOS capabilities and performance is implemented using MAOS.…”

Tip/tilt point spread function reconstruction for laser guide star multi-conjugate adaptive optics

“…In order to enable such science programs, AO systems on existing telescopes and future extremely large telescopes are required to meet tight photometry and ast rometry budgets. For instance, the multi conjugate adaptive optics (MCAO) system under de sign for the Thirty Meter Telescope (TMT) is required to provide 2% differential photometry over a 30'' field of view (FoV) for a 10 min integration at a wavelength of 1 micron, and 50 microarcsec root-mean-square (RMS) time dependent differential astrometry over the same FoV for a 100 sec integration in H band [7,8].…”