Mirror coating chamber complete
By Eva D. Blaylock, AFRL Directed Energy Directorate
/ Published December 13, 2006
KIRTLAND AIR FORCE BASE, N.M. --
The Defense Department's largest mirror-coating chamber was installed and testing completed recently at the Air Force Research Laboratory's Starfire Optical Range.
"This will give the laboratory a safer alternative to transporting the 3.5-meter (11.5 feet) mirror all the way to Kitt Peak Observatory in Tucson," said 1st Lt. Wellington Phillips, project officer for the coating chamber at the Directed Energy Directorate, Optics Division. "Since we now only have to move the mirror from the top of the mountain to the base, here, the risk of damage is far less to the $8 million dollar mirror - a size that isn't even made anymore."
"The laboratory had a need for the chamber," said Lieutenant Phillips, "but not enough funding." Thanks to a $1 million congressional add, the chamber was constructed at DynaVac in Boston and transported to the facility earlier this year. The chamber was designed to coat optics as large as 3.6-meters (11.8 feet).
The coating process uses tungsten filaments coils that are tailored with half-inch pieces of aluminum strategically placed in the chamber. The chamber is vacuum-sealed and then the coils are heated until the aluminum reaches its melting point. The heat causes the aluminum to evaporate and condense on the mirror, facing up in the chamber, creating a thin layer of coating to increase reflectivity. Preliminary testing has already taken place within the chamber, with aluminum being deposited on test slides.
"This is perfect timing for our mirror here. It is overdue for a new coating - though the mirror is well-taken care of and hasn't needed a new coating since it was first done in 1992. You could say that we are working on borrowed time," Lieutenant Phillips said. "Those who use mirrors for astronomy don't generally have the luxury to care for their mirrors as we do - they have to open theirs, rain or shine, if they want to look at objects. In inclement weather, we don't even open the dome."
The chamber includes a modifiable user interface written in LabView code that can be altered if the chamber needs to be modified. The chamber could possibly be used to coat mirrors for astronomy customers, such as Apache Point in Cloudcroft, N.M., Magdalena Ridge in Socorro, N.M., the National Solar Observatory in Sunspot, N.M., and the High Energy Laser Test Facility at White Sands Missile Range near Alamogordo, N.M.
With the installation of the chamber, the directorate now has two coating facilities available at Kirtland. The second chamber, located in the Optical Coating Engineering Laboratory, uses a different process to coat optics up to 2.5 meters (8 feet, 3 inches) and will provide specialized coatings to various commercial customers. Presently, the coating chamber at the SOR uses the thermal evaporation of bare aluminum coating method and will only be used for the laboratory's mirror and select astronomy customers.