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Germanium (Ge)

Germanium (Ge) Data Sheet     ♦ Germanium (Ge) MSDS     ♦ Germanium (Ge) FDS (French)

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.

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

To download this data or our MSDS safety data sheet as a pdf, please click on the links at the top of the page.  To expand the transmission graphs, please click on the image.

Click to access current Germanium Stock Windows
Click to access current Germanium Stock ATR Prisms 

µm   Noµm   Noµm   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

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