NFIRAOS (Narrow-Field InfraRed Adaptive Optics System) will be the first-light multi-conjugate adaptive optics system for the Thirty Meter Telescope (TMT). NFIRAOS supports three Near Infrared (NIR) client instruments, and provides exceptional image quality across the 2 arcminute field of view. In 2018, NFIRAOS passed the Final Design Review (FDR), but there have been several substantial changes more recently. The optical enclosure (ENCL) refrigeration design was updated for CO2 refrigerant, and an enclosure wall panel was prototyped. The polar-coordinate CCD for the laser guide star (LGS) wavefront sensor camera was replaced with a commercial C-Blue camera from First Light Imaging. More recently, the NFIRAOS Science Calibration Unit (NSCU), which was previously a separate Canadian contribution, was incorporated into the scope of NFIRAOS, and has progressed to the Conceptual Design level. In addition to these changes, the team has been working to bring the last of the low-risk subsystems to final design level in preparation for the beginning of construction.
NFIRAOS is the first-light adaptive optics system for the Thirty Meter Telescope (TMT). It features a laser guide star wavefront sensor system, which helps to correct atmospheric distortion over a 2 arc-minute field of view. Since the final design review for NFIRAOS in 2018, a trade-study was undertaken to consider a new camera from First Light Imaging called C-Blue One as the LGS wavefront sensor. A redesign of the LGS subsystem of NFIRAOS was undertaken to incorporate this new wavefront sensor into the design with updated AO tolerances, optics, and a new relay system to reimage a high density lenslet-array onto the small sensor.
NFIRAOS (Narrow Field InfraRed Adaptive Optics System) is the first-light adaptive optics system designed for the Thirty Meter Telescope (TMT). NFIRAOS includes a laser guide star wavefront sensor system (NLGS) which contains a trombone mirror assembly that compensates for the altitude fluctuations of the sodium layer and the elevation angle of the telescope. Within the trombone mirror assembly, there are two heavy fold-mirrors whose housings contain precision adjusters to align the laser guide stars with the wavefront sensors.
The adjusters must achieve a resolution of 10 μrad and a range of 1 mrad to satisfy the NFIRAOS requirements for laser guide star stability on the wavefront sensors. The adjuster design has many unknowns so a prototype of these adjusters was developed and tested to determine the best design and material selection for use in NLGS. It was found that, although the resolution is unpredictable, the designed adjuster can meet the NFIRAOS requirements with feedback from the optical alignment system. It was also found that material selection and grease are very important to prevent seizing of the adjusters. The results from testing will be used to improve upon the current NLGS adjuster design.
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