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Sapphire Single Crystal
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90° Crystal Orientation
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50-20 Scratch-Dig
ISI offers a wide selection of Sapphire Viewport assemblies suitable for high and
ultra-high vacuum applications. The use
of high purity sapphire and low expansion alloys enables these assemblies to be
repeatedly baked out at high temperatures
up to 450°C maximum.(2)
Sapphire is a synthetic, hexagonal single crystal anisotropic material which displays
substantially different physical, thermal, dielectric and optical characteristics
when measured along different axes.
Grades
All viewports up to one inch in diameter are offered with UV grade sapphire; those
exceeding one inch diameters are offered
with regular grade materials. UV grade material is available on request at additional
cost.
Note that limitations in today’s crystal growth technology make it difficult to
guarantee constant transmission performance at wavelengths below .25 microns.(3)
Surface Finish
Poor surface finish can contribute as much as 10% to overall transmission
losses. All viewports are supplied with flat
faces which have been finished to standards suitable for most applications. ISI’s
standard finish for sapphire viewports is a
50-20 scratch-dig. Other finishes are available on request at additional cost.
The optics industry typically recommends
a 20-10 scratch-dig optical finish for service below 0.25 microns.
Crystal Orientation
Crystal orientation of ISI Sapphire viewports is perpendicular to the windows
optical axis, which is also referred to as a
90° orientation. Assemblies with crystal orientation parallel to the windows optical
axis, 0° orientation, are available on request at additional cost.
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Sapphire Viewport Family
| General Specifications |
| Transmission Range:(1) |
|
| Regular Grade |
0.30 to 4.00µm |
| UV Grade |
0.25 to 4.50µm |
| Temperature Range:(2) |
|
| Weldable & Del-Seal CF |
to 450°C |
| ISO NW Kwik-Flange |
to 150°C |
| Sapphire Transmission Curve |
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Notes
(1) Transmission curves are approximations,
intended for reference only. They are based on a
1mm sample thickness as tested by Sapphire manufacturers.
(2) Thermal gradient should not exceed
25°C/minute.
(3) Extended UV and IR range viewports
are detailed in Section 7.4. |
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