Sapphire Viewports
Sapphire is a synthetic, hexagonal single crystal anisotropic
material which displays substantially different physical, thermal,
dielectric and optical characteristics when measured along different
axes. MDC sapphire viewports are constructed using 90° crystal
orientation, where the crystal orientation is parallel to a
window’s surface. Viewports with crystal orientation parallel to
the optical axis, or 0° orientation, can be custom ordered from Insulator
Seal.
MDC offers a wide selection of sapphire viewport assemblies
suitable for high and ultrahigh vacuum applications. The use of high
purity sapphire and nickel-iron low expansion alloys enables these
viewports to be repeatedly baked to temperatures as high as 450°C.
All sapphire viewports up to 1 inch in diameter use ultraviolet
grade sapphire material. Those exceeding 1 inch diameters are
supplied with regular grade sapphire.
Note that limitations in current sapphire crystal growth
technology make it difficult to guarantee constant transmission
performance at wavelengths below 0.25µm.
The sapphire viewports offered in this catalog are supplied with
flat faces polished to a 50-20 scratch-dig while quartz viewports
are 80-50 scratch-dig. Although these finishes are suitable for most
optical applications, the optics industry recommends a 20-10
scratch-dig finish for wavelengths below 0.25µm.
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