Germanium prisms specifications:
1 arc minutes
10 arc seconds
The transmittance range of optical germanium material is 2-14um, and its refractive index is as high as 4. Germanium lens and germanium window are widely used in thermal imaging system.
Because germanium material has high refractive index, the surface reflectivity is very high (R>30%), so optical germanium elements usually need AR coating.