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The Narrow Field InfraRed Adaptive Optics System (NFIRAOS) will be the first-light facility Multi-Conjugate Adaptive Optics (MCAO) system for the Thirty Meter Telescope (TMT). Historically, an important factor limiting the performance of an AO system has been the system vibrations and their impact on the delivered image quality. In order to leverage the extraordinary capabilities of the TMT, NFIRAOS must be capable of meeting the required optical performance and stability specifications while operating in the presence of the predicted vibration environments. Using the NRC-developed integrated modeling framework (NRCim), a detailed evaluation of the dynamic opto-mechanical performance of NFIRAOS was completed with several sources of structural disturbances (vibration from the telescope structure, from attached instruments, and internal to NFIRAOS). Multiple computational methodologies, including transient (time-series) and harmonic (transfer function) analyses combined with a Linear Optics Model (LOM), together with control system transfer functions for both common path and non-common-path disturbances were used to evaluate and compare the NFIRAOS delivered image quality. These procedures are described and the NFIRAOS performance in the presence of the various sources of vibration are reported. These sources include observatory vibration transmitted to NFIRAOS as well as internal sources such as the LGS WFS trombone, refrigeration, client instruments’ rotator and cable wrap., 6th International Conference on Adaptive Optics for Extremely Large Telescopes, AO4ELT 2019; June 9-14, 2019, Quebec City, 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 micro m 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 per cent sky coverage at the galactic pole with less than 187 nm wavefront error. Astrometry is an important science driver – to minimize image distortion (0.0017 per cent), we have recently revised the optical design to use four off-axis paraboloidal mirrors. We have vastly simplified the laser WFS trombone 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 degrees 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.

Vibration suppression in Astronomical Adaptive Optics (AO) systems has gathered great attention in the context of next-generation instrumentation for current telescopes and future Extremely Large Telescopes (ELTs). This paper focus on the application of a novel multi-rate algorithm formulated in [Correia et al., 2011] to the 1st-light Multi-Conjugate Adaptive Optics Facility (NFIRAOS) for the Thirty-Meter Telescope (TMT). Numerical simulations cover the case of vibration peaks in the [2-225] Hz range with variable peak width based on telemetry from the Keck observatory. A comparison to other vibration suppression algorithms is performed using control loop framerates in the range [20–800] Hz, required to sense natural guide stars with magnitudes from mv about {12 − 22} in H-band.

The thirty meter telescope (TMT) has the potential to find new and to study in greater detail nearby planetary systems. It could also possibly image super-Earth planets around the closest stars or still accreting distant protoplanets in very young star forming regions. Since no first generation dedicated exoplanet finding instrument has been selected for the TMT, initial direct exoplanet imaging will have to rely on the NFIRAOS facility adaptive optics (AO) system and IRIS spectro-imaging near-infrared (NIR) camera. End-to-end Fresnel NFIRAOS /IRIS simulations are presented using their current optical designs to evaluate the system multi-wavelength high-contrast imaging capabilities. Long exposures have been simulated using the expected AO-delivered phase screens and the estimated speckle lifetime. It is shown that NFIRAOS/IRIS may achieve contrasts comparable to the Gemini planet imager (GPI, an optimized NIR planet-finding instrument that will soon be installed on the Gemini South 8-m telescope), but needs to rely on multi-wavelength processing (by a factor 50) to achieve that goal, a challenging requirement. Without a coronograph and a better treatment of the in-band static speckle noise, NFIRAOS/IRIS will not be able to achieve GPI-like high contrast at a very small inner working angle, which is potentially accessible with a large 30-meter telescope. However, TMT, with its bigger aperture and better angular resolution, along with the current NFIRAOS/IRIS designs will acquire higher SNR spectra and will achieve an astrometric accuracy three times smaller than GPI for medium to bright planets, resulting in better atmospheric characterization and faster orbital parameter determination of a sample of GPI planets.

We have explored the feasibility of using the MRF polishing technique to produce large phase plates such as the 742x386mm phase plate required for NFIRAOS. QED Technologies’ MRF polishing machines can produce phase plates as large as 1100x900mm. This technology allows predetermined phase screen profiles to be polished onto glass substrates, yielding phase plates with welldefined turbulence profiles that are durable enough to be used in the cooled (-35C) NFIRAOS AO system for TMT. We present the measurements that we have obtained on a 200x200mm pathfinder prototype, manufactured by QED Technologies on a N-BK7 substrate. We find that the synthetic turbulence has the prescribed structure down to a spatial scale of 5mm. For scales smaller than 5mm and down to 0.5mm we measured about 20% less structure than prescribed making the generated turbulence useful even at those scales. Based on these results, we conclude that MRF polishing appears to be a very promising technique for producing large turbulence phase plates for ELT-class AO systems.