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Ge Crystal

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 100C. 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.

Maximum available size: 100 mm Dia x 50 mm Thk.

Germanium (Ge)

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BASE PROPERTIES
PARAMETER
VALUE
OPTICAL
Transmission Range
1.8 to 23 microns
Refractive Index
4.0026 at 11 microns
Reflection Loss
53% at 11 microns (2 surfaces)
Absorption Coefficient
1.3 x 10-3e cm-1 at 3.8 microns
dN/dT
-10.6 x 10-6e/C
dN/d = 0
R. I. almost constant
   
PHYSICAL
Density
5.33 g/cm3
Melting Point
936 C
Thermal Conductivity
58.61 W/(m*K)at 293K
Thermal Expansion
6.1 x 10-6e/C at 298K
Hardness
Knoop 780 kg/mm2 (100)
Specific Heat Capacity
310J/(kg K)
Dielectric Constant
16.6 at 9.37GHz at 300K
Young's Modulus (E)
102.7 GPa
Shear Modulus (G)
67 GPa
Bulk Modulus (K)
77.2 GPa
Elastic Coefficients
C11 = 129 C12 = 48.3 C44 = 67.1
Apparent Elastic Limit
89.6 MPa (13000psi)
Poisson Ratio
0.28
CHEMICAL
Solubility
Insoluble in water
Molecular Weight
72.59
Class/Structure
Cubic diamond, Fd3m
REFRACTIVE INDEX            
Wavelength, m
2.06
2.15
2.44
2.58
3.00
3.42
Refractive Index
4.10
4.09
4.07
4.06
4.05
4.03
Wavelength, m
4.36
6.24
8.66
9.72
11.04
13.02
Refractive Index
4.03
4.01
4.00
4.00
4.00
4.00
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Ge Crystal