Ge(CRYSTRAN) Refractive Index

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. Germanium 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. Germanium can be AR coated with Diamond producing an extremely tough front optic.

Germanium is grown using the Czochralski technique by a small number of manufacturers in Belgium, USA, China and Russia. The refractive index of Germanium changes rapidly with temperature and the material becomes opaque at all wavelengths a little above 350K as the band gap floods with thermal electrons.

REFERENCES:

(1) Handbook Optical Constants, ed Palik, V1, ISBN 0-12-544420-6

(2) Li, Refractive Index of Germanium etc, J.Phys Chem, V9, p561, 1980

(3) Pearson & Brattain, Proc. Inst. Radio Eng. V43, p1794, 1955
(4) Fine, J.App.Phys, V24, p338, 1953

(5) Wortman & Evans, V36, (1), P153 (1965)

(6) Hawkins, Sherwood, Djotni: Mid IR Filters for astronomical and remote sensing instrumentation. Invited Paper SPIE Conference Glasgow 2008

(7) Manufactures Published Data