Coating Tested for Large Binocular Telescope

Bruce Atwood and his team at Ohio State University's Imaging Sciences Laboratory in Columbus are beginning full-scale tests of coating equipment designed to aluminize the two 8.4-m primary mirrors for the Large Binocular Telescope. The system will be shipped to the telescope's construction site on Mount Graham near Safford, Ariz., by February 2004.

Atwood explained that the specifications for the final mirrors call for a 1200-Å-thick coat of aluminum with a uniformity of ±10 percent over 1 m and better at smaller scales. The aluminum to be deposited will be heated in an array of 25 boron-nitride crucibles to offer higher reproducibility than tungsten filaments. He noted that the addition of hydrogen to the 22-ton vacuum chamber scatters the evaporated aluminum, which enables the use of fewer sources and small source/mirror spacing.