2001-Jun-25
Sensitive radio receivers operating at frequencies above approximately 100 GHz require the use of cryogenic detectors, often SIS mixers, cooled to liquid helium temperatures. A vacuum window is required to couple the radiant energy through the chamber walls to the detector element with as little loss as possible. While seemingly simple to make, the optimization of windows for high transparency and low leak rate is a non-trivial problem requiring the construction of multilayer dielectric structures.
The Atacama Large Millimeter Array (ALMA) telescope, to be built in Chile, will require over 600 vacuum windows covering ten frequency bands. In support of ALMA and its own in-house development needs, NRAO has developed a number of crystal quartz vacuum windows utilizing Zitex, Goretex, Teflon and other plastic anti-reflection coatings to improve the window's overall transmission within specific bands. The design, fabrication details and testing of some of these windows are discussed.
View a pdf version of ALMA Memo 377.
Last modified: June 25, 2001
alma-memos@nrao.edu