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Entrance Window

NIRI Optical Overview - Entrance Window
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The NIRI entrance window is made of CaF2 and is 180mm in diameter and 20mm thick with radius of curvature of 4000mm on both surfaces. The outer window surface is at ambient temperature/pressure while the inner surface will reach cryogenic temperatures at vacuum (<10^-5 torr). The window provides a clear aperture of 145mm diameter and has a wedge tolerance specification of <0.5 arcminutes. The outer surface is anti-reflection coated for the 1-5.6um wavelength range.

In the photograph below, the entrance window aperture is shown covered by a plexiglass disk to keep moisture from condensing on the CaF2 window during testing at sea-level. This will be removed when NIRI is in use on Gemini. Through the window can be seen the focal-plane pin-hole mask used in image quality characterisation.

[NIRI Entrance Window]

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Last update June 27, 2000; Colin Aspin