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Viewports - Sapphire - Introduction

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.

Insulator Seal (ISI) brand catalog and custom engineered ceramic to metal seal products are manufactured to ISO 9001:2015 standard utilizing our qualified hermetic brazing and joining processes.

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
Sapphire Transmission Curve image
(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.
Product Links
Grade Mounted On
UV Grade Sapphire Del-Seal™ CF
Kwik-Flange™ KF
Sapphire Del-Seal™ CF
Kwik-Flange™ KF
Related Links
Go to Viewports Introduction


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.