Ge (Germanium)

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.

Physical and optical properties  

Transmission Range :	1.8 to 23 μm (1)
Refractive Index :	4.0026 at 11 μm (1)(2)
Reflection Loss :	53% at 11 μm (Two surfaces)
Absorption Coefficient :	<0.027 cm-1 @ 10.6 μm
Reststrahlen Peak :	n/a
dn/dT :	396 x 10-6 /°C (2)(6)
dn/dμ = 0 :	Almost constant
Density :	5.33 g/cc
Melting Point :	936 °C (3)
Thermal Conductivity :	58.61 W m-1 K-1 at 293K (6)
Thermal Expansion :	6.1 x 10-6/°C at 298K (3)(4)(6)
Hardness :	Knoop 780
Specific Heat Capacity :	310 J Kg-1 K-1 (3)
Dielectric Constant :	16.6 at 9.37 GHz at 300K
Youngs Modulus (E) :	102.7 GPa (4) (5)
Shear Modulus (G) :	67 GPa (4) (5)
Bulk Modulus (K) :	77.2 GPa (4)
Elastic Coefficients :	C11=129; C12=48.3; C44=67.1 (5)
Apparent Elastic Limit :	89.6 MPa (13000 psi)
Poisson Ratio :	0.28 (4) (5)
Solubility :	Insoluble in water
Molecular Weight :	72.59
Class/Structure :	Cubic Diamond, Fd3m

 

Refractive Index  

No = Ordinary Ray

µm	No	µm	No	µm	No
2.058	4.102	2.153	4.0919	2.313	4.0786
2.437	4.0708	2.577	4.0609	2.714	4.0562
2.998	4.0452	3.303	4.0369	4.258	4.0216
4.866	4.017	6.238	4.0094	8.660	4.0043
9.720	4.0034	11.04	4.0026	12.00	4.0023
13.02	4.0021

Product Notes

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.
 

Tags: Ge (Germanium)

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