This paper provides an update on the progress in designing, prototyping, modeling, and manufacturing the TMT first light AO systems and their AO components. Key highlights encompass the completion of the preliminary design of the Laser Guide Star Facility, the fabrication of the NFIRAOS deformable mirrors, the study of the petalling modes impact and associated mitigations for TMT, and the development of the first light verification plan, and assessment of the expected performance.
The Laser Guide Star Facility (LGSF) system of the Thirty Meter Telescope (TMT) will generate up to 8 artificial laser guide stars in the mesospheric sodium layer with the brightness, beam quality, and asterism geometries as required by both the TMT first light AO system and future AO instruments. It includes the sodium lasers mounted on the telescope elevation structure below the primary mirror, the conventional beam transfer optics system to transport the beams up to the telescope top end, and the formatting and launching optics to project the required laser guide star asterism to the sky using a center launch telescope located behind the secondary mirror. In this paper, we will present the recent successful completion of the LGSF preliminary design, including: the optical, mechanical, electronics, safety, control, and software designs; the systems engineering; the modeling activities; and the next steps for the system’s final design phase including prototyping.
An aerothermal modeling framework was developed for the entire TMT International Observatory Laser Guide Star Facility, consisting of several standalone conjugate heat transfer models: laser head, laser bench array, optical path pointing arrays, beam transfer duct, top end including the laser telescope assembly, and several electronics cabinets, resolving all interior components. The primary goals were to evaluate the focus error from the thermal lens deformation, to evaluate beam jitter from the optical path difference maps along the beam path, and to obtain the temperature of all exterior surfaces. The framework provided performance sensitivity to specific inputs/assumptions and lead to improved design that meets performance requirements.
The TMT Laser Guide Star Facility (LGSF) system is responsible for generating the artificial guide stars in the mesospheric sodium layer with the brightness, beam quality and asterism geometries required by both the first light AO system and future AO instruments. It includes the sodium lasers mounted on the elevation structure, the beam transfer optics to transport the beams up to the telescope top end, and the formatting and launching optics to project the required laser guide star asterism to the sky using a center launch telescope. In this paper, we will present the LGSF preliminary design including the design trade-offs, the optical, mechanical, electronics and software design, as well as the modeling activities.
NFIRAOS (Narrow-Field InfraRed Adaptive Optics System) will be the first-light multi-conjugate adaptive optics system for the Thirty Meter Telescope (TMT). NFIRAOS houses all of its opto-mechanical sub-systems within an optics enclosure cooled to precisely -30°C in order to improve sensitivity in the near-infrared. It supports up to three client science instruments, including the first-light InfraRed Imaging Spectrograph (IRIS). Powering NFIRAOS is a Real Time Controller that will process the signals from six laser wavefront sensors, one natural guide star pyramid WFS, up to three low-order on-instrument WFS and up to four guide windows on the client instrument’s science detector in order to correct for atmospheric turbulence, windshake, optical errors and plate-scale distortion. NFIRAOS is currently preparing for its final design review in late June 2018 at NRC Herzberg in Victoria, British Columbia in partnership with Canadian industry and TMT.
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