It blocks UV and visible light,as well as IR up to about 2μm.

Its high index is desirable for the design of lenses that might not otherwise be possible.

It has nearly the highest density of the IR-transmitting materials, a consideration when designing for weight restricted systems.

It is subject to thermal runaway; the hotter it gets, the more the absorption increases. Pronounced transmission degradation starts at about 100°C and begins rapidly degrading between 200°C and 300°C, resulting in possible catastrophic failure of the optic.

Ge is generally less expensive than ZnSe and Cleartran.

Ge is diamond turnable.

Typeical application: Thermal imaging, FLIR.

Products manufactured:Lenses, Aspheric Lenses, Binary (Diffractive) Lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges.

Surface finish:Typical specifications for surface quality in the infrared are 40-20 or 60-40 scratch dig in the 2 to 7μm spectral region and 60-40, 80-50 or 120-80 scratch- dig for the 7-14μm area, depending upon system performance requirements. Diamond turned surface finishes of 120 Angstroms rms or better are typical.

Surface figure:Surface figure: In the infrared, typical surface figure ranges from 1/2 wave to 2 waves @0.6328μm depending on the system performance requirements.

AR coating options: Typical available coatings for Germanium include BBAR for 3 to 5μm, 8 to 12μm, and the 3 to 12μm spectral regions. Many application specialized bands are possible between the 2 and 14μm.