The anti-reflective coating on the sapphire window reduces transmission loss and improves scratch resistance.
1. The sapphire substrate has a high refractive index, so it is usually necessary to coat the sapphire window with an anti-reflective (AR) coating to have sufficient transmittance in the area of interest.
2. Sapphire windows usually need to work under extreme conditions, so a hard antireflection coating is needed to withstand harsh environmental conditions and improve scratch resistance.
Metalized sapphire windows can be used to create sealed optical components for equipment applications that require harsh vacuum environments. It can also be used in some equipment that needs to weld or bond the sapphire window to metal.
Synthetic sapphire has single crystal high purity, so bare sapphire will not be attached to brazing or solder alloy alone. It is necessary to plate a thin layer of chromium and nickel alloy around the edge of the sapphire window.
The metalized edge forms a surface that enables the sapphire window to be brazed into the metal casing. Brazing is the use of molten filler metal to bond two unmelted characters. It forms a firm bond between surfaces with small gaps and is particularly suitable for sapphire window assembly applications. When the sapphire window is completed correctly, the joint is sealed.