At the University of Arizona's Richard F. Caris Mirror Laboratory, a team of scientists and engineers is making giant, lightweight mirrors of unprecedented power for a new generation of optical telescopes.
These mirrors represent a radical departure from the conventional solid-glass mirrors used in the past. They have a honeycomb structure on the inside; made out of Ohara E6-type borosilicate glass that is melted, molded and spun cast into the shape of a paraboloid in a custom-designed rotating oven. Honeycomb mirrors offer the advantages of their solid counterparts - rigidity and stability - but they can be significantly larger, and dramatically lighter.
The Mirror Lab team has also developed a revolutionary new method to polish the honeycomb mirrors with a deeply curved, parabolic surface that results in much shorter focal lengths than conventional mirrors.
The pioneering work being done today at the Mirror Lab had its beginning around 1980 with a backyard experiment by Dr. Roger Angel, the lab's founder and scientific director. Curious about the suitability of borosilicate glass (the kind used in glass ovenware) for making honeycomb structures, he tested the idea by fusing together two custard cups in an improvised kiln. The experiment was a success and led to a series of bigger kilns and small furnaces and, eventually, the spin casting of three 1.8 meter mirrors.
By 1985, with financial support primarily from the US Air Force, the National Science Foundation and the University of Arizona, Roger Angel and a talented Mirror Lab team moved to the current facility under the east wing of the UA football stadium. A large, rotating furnace was built and a series of mirrors as big as 3.5 meters in diameter were successfully cast.
By 1990, the rotating furnace was expanded to its current size, and a new wing was added to the Mirror Lab to house two mirror polishing stations and a test tower. The new furnace, which is large enough to cast mirrors up to 8.4 m in diameter, was first used in 1992 to make a 6.5-m mirror. In January 1997 the first 8.4-m mirror for the Large Binocular Telescope (LBT) was completed.
The Mirror Lab continues its impressive history of successful, ground breaking mirror castings with the Giant Magellan Telescope. This telescope will be the largest and most advanced earth-based telescope in the world when complete. Currently, three of the seven, 8.4 meter segmented mirrors have been cast. The first mirror is complete and the other two are in various stages of production. On September 18, 2015 the fourth center-primary mirror was cast at the mirror lab.