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Home > Products > Optical Products > Optical Materials > Germanium |
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Germanium
| Germanium (Ge) is the preferred lens and window material for high performance infrared imaging systems in the 8~12 ¦Ìm wavelength band. 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 2~12 ¦Ìm range. Its transmission is very temperature sensitive, becoming opaque near 100¡ãC. Environment does not cause problems because Germanium is inert, mechanically rugged, and fairly hard.
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.
Application as window, lens, beamsplitter, ATR prism or filter in spectrometers and in thermal imaging. |
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| Main Properties |
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| Crystal Properties |
| Crystal Growth Method |
Czochralski (CZ) pulling techniques |
| Maximum Size |
<¦Õ250mm |
| Optical Properties |
| Transmission Range |
1.9~17µm |
| Reflection Loss, for two surfaces at 11µm |
53% |
| dn/dt (@633nm), /¡ãC |
396x10-6 |
| dn/d¦Ì=0 |
R.I. almost constant |
| Refractive Index |
See below |
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Wavelength (µm) |
Refractive Index (n) |
Wavelength (µm) |
Refractive Index (n) |
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2.0 |
4.1079 |
9.0 |
4.0047 |
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3.0 |
4.0446 |
10.0 |
4.0040 |
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4.0 |
4.0242 |
11.0 |
4.0031 |
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5.0 |
4.0153 |
12.0 |
4.0029 |
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6.0 |
4.0106 |
12.5 |
4.0024 |
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7.0 |
4.0076 |
13.02 |
4.0021 |
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8.0 |
4.0053 |
15.0 |
4.0017 |
| Transmission Curve |
See below |
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| Crystallographic Properties |
| Syngony |
Cubic |
| Crystal Form |
Polycrystalline or Monocrystalline |
| Lattice Constant, Angstrom (Å) |
5.66 |
| Cleavability |
<111>, non-perfect |
| Physical Properties |
| Density, at 20 ¡ãC |
5.33 |
| Mohs Hardness |
6.3 |
| Dielectric Constant for 9.37x109 Hz at 300 K |
16.6 |
| Melting Point, ¡ãC |
937 |
| Thermal Conductivity, W/m¡¤K at at 293 K |
59 |
| Thermal Expansion, 1/K at 298 K |
6.1x10-6 |
| Specific Heat Capacity, J/(KgK) at 273-373 K |
0.074 |
| Bandgap, eV |
0.67 |
| Knoop Hardness, Kg/mm2 |
800 |
| Youngs Modulus, Gpa |
102.66 |
| Shear Modulus, GPa |
67.04 |
| Bulk Modulus, GPa |
77.86 |
| Debye Temperature, K |
370 |
| Poissons Ratio |
0.278 |
| Elastic Coefficient |
C11=129, C12=48.3, C44=67.1 |
| Apparent Elastic Limit |
89.6 MPa (13000psi) |
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Chemical Properties |
| Chemical Formula |
Ge |
| Molecular Weight |
72.59 |
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Solubility in water |
None |
| Solubility in acids |
Soluble | | |
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