鍺(Germanium,簡稱Ge)
Germanium is a high index material that is used to manufacture Attenuated Total reflection (ATR) prisms for spectroscopy. Its refractive index is such that germanium makes an effective natural 50% beamsplitter without the need for coatings. It is also used extensively as a substrate for production of optical filters. Germanium covers the whole of the 8-14 micron thermal band and is used in lens systems for thermal imaging. It can be AR coated with diamond producing an extremely tough front optic. Its transmission is very temperature sensitive, becoming opaque near 100°C. Environment does not cause problems because Germanium is inert, mechanically rugged, and fairly hard.
Germanium is grown by Czochralski pulling techniques. It is relatively expensive. The refractive index changes rapidly with temperature and material becomes opaque at all wavelengths a little above 293K.
