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.
The Narrow Field Infrared Adaptive Optics System (NFIRAOS) within the Thirty Meter Telescope (TMT) will unlock new potential for ground-based astronomy. This subsystem is a series of optics that correct for atmospheric turbulence seen in the Infrared wavelength. One of the critical challenges in the NFIRAOS system is the ability to operate at -30 degrees Celsius. The use of RTV (Room Temperature Vulcanizing) silicone as an adhesive allows a more flexible bond between the optic and its mount. This material is capable of withstanding temperature changes without losing bond strength. Additionally, the large Off Axis Parabola (OAP) mirrors provide a unique technical challenge in their mounting configurations. The optics have with a mass of 90 kilograms and must be mounted able to withstand a 50-degree temperature differential from their ambient temperature bonding. This paper builds of initial conceptual and prototyping work done by ABB and provides the next steps scaling towards a final design of large RTV bondspot optical mounting. Through a combination of simulations, iterative prototyping, room temperature and operational temperature stress testing, a final design proposal is presented backed by statistical and in-house life cycle testing methods. The findings in this work have applications as the industry moves towards mounting larger optics in increasingly challenging environments.
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