Custom engineered and fabricated sapphire viewport windows that can be metalized, brazed and sealed into Kovar® and stainless steel sleeves are available from Meller Optics, Inc. of Providence, Rhode Island.
Meller Sapphire Viewport Windows feature Moh 9 hardness and can operate from UHV to 10,000 psi at temperatures from cryogenic to 1,000 degrees C, depending upon configuration.
Meller Sapphire Viewport Windows feature Moh 9 hardness, which is second only to diamond, and can operate from UHV to 10,000 psi at temperatures from cryogenic to 1,000°C, depending upon configuration. Custom fabricated to assure a reliable seal, they are manufactured to specification with stepped edges and elliptical edge shaping, holes, slots, and wedges for mounting.
Available in flat and spherical configurations from 1/4” to 10” dia. and 1/2 mm to 1” thick with A/R coatings, Meller Sapphire Viewport Windows feature flatness of 0.5 fringes HeNe and parallelism from 20 to 2 arc/secs. Resistant to chemicals (fluorine to 300°C) and most acids, these sapphire viewports are impervious to water, blowing dirt, and sand.
Meller Sapphire Viewport Windows are priced according to configuration, size, and quantity. Price quotations and complete material specifications are available upon request.
Source: http://www.melleroptics.com