Measurement data and evaluation result of CLEARCERAM-Z 1.5m diameter mirror blanks for the TMT M1 segment blanks

Astronomy has a long history, and ancient civilizations established calendars based on observations of celestial bodies by eye. Humans continued to observe celestial bodies, but in the 17th century, a major breakthrough was made. This was the invention of the telescope. It made it possible to observe celestial bodies that could not be seen with the naked eye, and it became the foundation of modern science. Since then, astronomical telescopes have evolved from refracting telescopes, which use optical lenses, to reflecting telescopes, which use mirrors. The size and performance of the primary mirror is one of the most important factors in the observing capabilities of a reflecting telescope. The Thirty Meter Telescope (TMT), which is currently under construction, will have the world's largest primary mirror at 30 meters when completed, and is expected to make a significant contribution to the development of astronomy. Ohara supplies the zero-expansion material used for this primary mirror. In this paper, we present the results of measurements and inspections of the coefficient of thermal expansion (CTE), residual stress, bubbles, and foreign matter, etc., for the 357 1.5-meter-long blanks of Ohara CLEARCERAM™-Z produced for the primary mirror of the TMT.