Its high refractive index makes Ge ideal for low power imaging systems because of minimum surface curvature. Chromatic aberration is small, often eliminating the need for correction. Germanium is most widely used for lenses and windows in IR systems operating in the 2μm-12μm range. 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 μm thermal bands and is used in lens systems for thermal imaging. It can be AR coated with diamond producing an extremely tough front optic.
Physical and optial properties:
Crystal Type
|
Cubic
|
Lattice Parameter
|
a=5.657Å
|
Transmission Band
|
2-12μm
|
Mohs Hardness
|
6.3
|
Density
|
5.33g/cm3
|
Melting Point
|
937 ℃
|
Refractive Index
|
4.0032 at 10.6μm
|
Resistivity
|
5-40 ohm-cm
|
Young's Modulus
|
103 GPa
|
Thermal Expansion
|
6.1x10-6/℃
|
Thermal Conductivity
|
167mcal/cm/s/k
|
Specifications:
Material:
|
Ge
|
Dimension Tolerance:
|
+0.0/-0.1mm
|
Thickness Tolerance:
|
±0.1mm
|
Surface quality:
|
60/40
|
Clear Aperture:
|
>85%
|
Flatness:
|
λ/2@633nm
|
Parallelism:
|
3'
|
