Schott has produced its 500th M1 primary mirror segment for the world’s largest optical telescope.

The European Southern Observatory’s Extremely Large Telescope (ELT) is currently under construction on the Cerro Armazones Mountain in Chile’s Atacama Desert.

The ELT will be the largest optical telescope in the world with a 39-meter primary mirror.

The mirror segments are composed of Schott’s glass ceramic Zerodur material, which can endure extremely high thermal exposure and has a long history of success in mechanical stability, making the glass a perfect use for astronomy.

In total, Schott will be producing 949 M1 hexagonal segments for the telescope, which is expected to see its first light by 2027.

Thomas Werner, Head of the ELT Project at Schott, welcomed the production milestone: “We are very proud to help shape the future of astronomy by supporting the European Southern Observatory in their important work on the ELT.”

Schott signed a contract with ESO in 2017 to supply at total of 949 Zerodur mirror blanks for the ELT’s M1 primary mirror, including 798 mirror blanks, 133 spare and 18 prototype segments; the first prototypes were delivered in 2019.

Series production for the ELT at SCHOTT’s Mainz, Germany headquarters began in 2020, and the final mirror blanks will be produced in early 2024.

In addition to the M1 mirror blanks, Zerodur will also feature on the ELT’s convex M2 mirror (4.2 meters), concave M3 mirror (3.8 meters), and adaptive M4 mirror (2.4 meters).

After production by Schott, the mirror blanks are shipped to French company Safran Reosc for polishing.

Schott will be presenting on Zerodur at the SPIE Astronomical Telescopes + Instrumentation conference in Montreal, Canada from 17 to 22 July.