Germanium has the property of thermal runaway, meaning that the transmission decreases as temperature increases. As such, Ge window should be used at temperatures below 100°. The higher Knoop Hardness of Germanium (780) makes it ideal for IR applications requiring rugged optics. Germanium's high density (5.33g/cm3) should be considered when designing for weight-sensitive systems.
Clear aperture: ＞80% of central diameter
EFL: +/- 1%
Centration: ＜ 3 arc minutes
Surface quality: 60-40 scratch and digs
Bevel : Protective bevel