[asac] [almanews] ALMA Memo No. 377 Released

[Carolyn White]

Design and Fabrication of Quartz Vacuum Windows
With Matching Layers for Millimeter-Wave Receivers

Daniel Koller, A. R. Kerr, G. A. Ediss, and D. Boyd

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.

     http://www.alma.nrao.edu/memos/html-memos/alma377/memo377.pdf


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