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 (Ge) is most widely used for lenses and windows in IR systems operating in the 2 - 12 µm range. Enviroment does not make any problems because Germanium is inert, mechanically rugged, and fairly hard. It is an excellent choice for multi-spectral systems and for applications where EMI shielding is necessary. Germanium can be electrically heated for anti-fogging or anti-icing applications.
      Silicon (Si) is commonly used as a substrate material for infrared reflectors and windows in the 1.5 - 8 µm region. The strong absorption band at 9 µm makes it unsuitable for CO2-laser transmission applications but it is frequently used for laser mirrors because of its high thermal conductivity and low density. Silicon is also a usefull transmitter in the 20 µm range. Silicon is used as an optical window primarily in the 3 to 5 micron band and as a substrate for production of optical filters. Large blocks of Silicon with polished faces are also employed as neutron targets in Physics experiments.

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