SCHOTT to manufacture mirror substrate for world's largest solar telescope

Mainz, Germany--SCHOTT has been selected by the Association of Universities for Research in Astronomy (AURA; New York, NY) to build the 4-meter primary mirror blank for Advanced Technology Solar Telescope (ATST) in Maui, Hawaii, which will be the world's largest solar telescope. To obtain ultra-sharp images of the flaming celestial sphere, researchers need a cool and undistorted view. The primary mirror substrate that is as thin as 76 mm and 4.25 m in diameter will be made out of Zerodur material from SCHOTT. The glass-ceramic with zero thermal expansion already delivers exact measurement data and precise images in solar telescopes like GREGOR, Sunrise, and Big Bear New Solar Telescope.

Astronomers plan to build the world’s largest solar telescope on Haleakala in Maui, Hawaii. The air is exceptionally clear, dry and still here, in the middle of the Pacific, more than 3000 m above sea level--ideal conditions for a terrestrial telescope to observe the full scope of electromagnetic activities on the surface of the sun. The project is funded by the U.S. National Science Foundation.

Construction of the ATST is scheduled to begin following the permitting process of the Hawaiian Department of Land and Natural Resources with operation anticipated for 2018. The primary mirror has a diameter of 4.25 m, which will be masked to a clear aperture of 4 m, and focuses the incoming sunlight through a heat stop then into the telescope's optical system.

The curved primary mirror substrate will be made of the Zerodur glass-ceramic from SCHOTT and is approximately 76 mm in thickness at its thinnest point. This allows the mirror to be easily adjusted using the actuators on its backside, but also to cool it to ambient temperature to reduce image distortion.

"Our glass-ceramic features the outstanding characteristic of having a coefficient of thermal expansion that is close to zero," said Thomas Westerhoff, head of the Zerodur product group at SCHOTT. "This allows for light to be reflected without being distorted. Besides, this glass-ceramic is extremely stable with respect to its shape and, with a specific density of 2.53 grams per cubic centimeter, even lighter than aluminum," he notes.

SOURCE: SCHOTT; www.us.schott.com/english/news/index.html?NID=350

--Posted by Gail Overton; [email protected]; www.laserfocusworld.com