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Michelle Entrance Window
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Michelle uses an entrance window made of Potassium
Bromide (KBr). KBr has a transmission of ~90%
across the mid-infrared. Since KBr is
hygroscopic, all contact between water with the
window must be minimized. This includes dew
that may form on the window while observing
under high humidity conditions. The humidity
limit for observing with Michelle at Gemini is
a relative humidity of 80%. During its use at
UKIRT, a protective "sacrificial window" system
was implemented to help prevent damage to the
cryostat window that serves as the vacuum seal
between the dewar and the atmosphere.
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Last update 23 August 2006; A. Verma & R. Mason