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TMT’s Laser Guide Star Facility Preliminary Design Review participants. Nearly 30 engineers and scientists attended the review in person at the Pasadena Project Office or remotely. The international review panel included experts from ESO, Durham University, NRC, and TIO. Image credit: TMT International Observatory

TMT Laser Guide Star Facility Proceeds to Final Design Phase

The TMT Laser Guide Star Facility (LGSF) has successfully completed its Preliminary Design Review (PDR) and is advancing to the Final Design Phase.  A panel of external and internal experts conducted the review on 8–9 November 2023 at the TMT International Observatory Project Office.

The TMT LGSF plays a crucial role in producing artificial laser guide stars that are essential to TMT’s Adaptive Optics (AO) systems, including NFIRAOS, the Observatory’s first-light AO facility. LGSF uses eight sodium lasers with a wavelength of 589 nm to generate laser guide stars for four distinct geometric configurations, or asterisms. These asterisms are projected onto the sky from a laser launch telescope positioned behind the TMT secondary mirror. Through the excitation of mesospheric sodium atoms at an altitude of approximately 90 km, the lasers generate artificial stars with the necessary brightness to provide AO correction for a wide range of scientific targets across the sky.

The Earth’s atmosphere is the largest barrier between ground-based telescopes and the stars. It generates turbulence that blurs the light and gives stars their twinkling appearance. The combination of TMT’s NFIRAOS system with LGSF will enable IRIS and MODHIS, TMT’s first-light AO instruments, to acquire images of astronomical objects nearly anywhere in the sky with the optimal sharpness of a thirty meter telescope, overcoming the limitations imposed by atmospheric turbulence.
The TIO AO group, with support from the System Engineering group, is responsible for the preliminary design of the LGSF. Due to resource constraints, the design process has been split into two phases. The first phase of the preliminary design focused on the LGSF optical, mechanical, and electronics design and was concluded with a successful PDR1 review in April 2021. In the second phase, the LGSF design team addressed recommendations from the LGSF PDR1 review, optimized the optical, mechanical, and electronics design through extensive simulations, and developed the LGSF software, safety measures, laser cooling, installation and maintenance tools (jigs and fixtures), and preliminary maintenance design including development planning.
“Congratulations to the LGSF Team for a successful LGSF PDR,” said Gelys Trancho, TMT LGSF PDR review chair and TMT project system engineer. Adding a special note to the review report, Trancho concluded, “There is a profound sense of appreciation for the LGSF
team's ability to effectively implement all TMT Systems Engineering processes. This application of processes has not only adhered to the required standards but has also resulted in an enhanced design. This accomplishment is noteworthy and demonstrates a commendable level of skill and teamwork.”
“This marks a significant milestone for TMT, and we are looking forward to developing the LGSF final design," added Corinne Boyer, TMT LGSF design team manager and Adaptive Optics group leader.


Overview of the TMT Laser Guide Star Facility (LGSF) system.

Overview of the TMT Laser Guide Star Facility (LGSF) system. The LGSF, mounted on the telescope structure, projects powerful laser beams into the Earth’s upper atmosphere, generating artificial stars to facilitate adaptive optics correction for atmospheric turbulence. Image credit: TMT International Observatory

TMT Laser Guide Star Facility Storyboard The image animation showcases an overview of the Laser Guide Star Facility installed on the telescope structure. The TMT LGSF comprises the Laser System, Beam Transfer Optics, Laser Launch Telescope system, and the associated Laser Safety system. Video credit: TMT International Observatory / Josh Church


The TMT LGSF design team thoroughly addressed each sub-system, integrating reliable technologies and meticulously developing the design of all components to ensure the success of the TMT Laser Guide Star Facility.
TMT LGSF Design Team Members
Corinne Boyer (Project Manager, Systems Engineering)
Lianqi Wang (Systems Engineer, Lead Optical/Control/Software Designer)
Melissa Trubey (Lead Mechanical Engineer)
Benjamin Irarrazaval (Lead Electronics/Safety/Laser Cooling Designer)
John Miles (Systems Engineering)
Konstantinos Vogiatzis (LGSF CFD Analysis)
Fernando Santoro (Mechanical Engineer)
Angelic Ebbers (Software Engineer)


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