Optical grade germanium
The optical grade germanium is required for high performance thermal imaging electron-optical systems. This material is widely used in thermal imaging systems and has become the predominant optical component. Optical grade germanium Ge has good transmission in 2-15 µm range. Due to high refractive index Ge lenses became very useful components of IR imaging systems operating in spectral region 3-14 microns.
Optical grade germanium can be of either polycrystalline or monocrystalline. Both monocrystalline and polycrystalline germanium Ge may be used for manufacturing of optical components. Germanium is a semiconductor material that can be either n or p-type. However, the n-type absorption coefficient is much lower making it the choice for IR applications. Although germanium has a very good internal transmittance and thermal conductivity, it is not suitable for a wide range temperature application due to its large temperature dependent refractive index.
Optical grade germanium Ge is used in a variety of applications in the optics industry. Germanium Ge uses are lasers, microscope objective lenses, ATR prisms, detector windows, IR polarizers. Germanium Ge is a diamond turntable material, what allows to produce aspheric and diffractive surfaces on germanium lenses. See Novotech webpages: “Spherical and aspheric lenses” and” Diamond turning. IR Optics”
NOVOTECH, INC. can supply germanium for optical and electronic applications in single (monocrystalline) or polycrystalline form. (Please sees the standard specifications for Optical Grade germanium below.)
Novotech has the capacity to perform diamond turning, polishing, and custom manufacturing for all size orders from prototype to production quantity.
Physical and mechanical properties of Germanium (Ge)
Thermal properties of Germanium (Ge)
Typical optical grade Germanium transmission
(sample thickness 2 mm)
Typical Germanium (Ge) coefficient of absorption
EMI grade germanium (Ge) exhibits a slightly higher absorption coefficient at room temperature 20°±3° than material with higher resistivity.
EMI Grade germanium (Ge) absorption coefficient degrades less than Optical grade germanium (Ge) resistivity 10-20 Ohm/cm absorption coefficient with temperature.
The worst absorption coefficient measurements are seen in the > 11µm and is reflected in the average absorption coefficient from 8-12µm and 7.5-13µm waveband.
70°C testing was not performed in a 70°C environment, therefore the results aren’t exact, but they do showcase the clear correlation between resistivity and transmittance at high temp. The sample being tested was heated in an oven to temperature > 70°C and then transferred to the spectrophotometer to be tested once a thermometer read 70°C when being shot directly at the sample as it cools.
Transmission of germanium (Ge) vs Temperature
Absorption Coefficient of germanium (Ge) vs Temperature
Refractive index of germanium (Ge)