Accu-Glass Products' Sapphire vacuum viewport flanges are rated for both high and ultrahigh (UHV) vacuum applications.
The use of high purity sapphire and low expansion alloys allow these viewports to be repeatedly baked out at temperatures up to 350°C. Sapphire is a synthetic, hexagonal single crystal anisotropic material which displays substantially different physical, thermal, dielectric and optical qualities when measured along different axes. Crystal orientation of Accu-Glass Products' viewports is normal to the optical axis or 90° orientation.
UV grade sapphire has a transmission range of 0.250µm to 4.50µm while regular sapphire has a transmission range of 0.30µm to 4.00µm. 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 a 50-20 scratch-DIG. Thermal gradients should not exceed 20°C per minute.