Germanium - bring minimal chromatic aberration.
Ge shows good transmission in 2-15μm range. Attributed to its high refractive index making low dispertion, the lens made of Ge brings minimal chromatic aberration and is very popular for IR systems operating in the 3-5 or 8-12μm spectrum. Ge is also good electromagnetic interference (EMI) shielding material. The EMI grade Ge windows with low resistance of 4-6 ohms is able to shield against electromagnetic interference within millimeter and centimeter ranges, make the IR system show better performance.
Ge blocks UV and visible light, as well as IR up to 2μm. Its density 5.323 gram/mm³ is highest in the IR transmitting materials, these properties limit it to be used in visible or NIR light combination and weight restricted systems.
Ø Germanium covers both atmosphere windows of 3-5 and 8-12μm, in additional its high refractive index, make Ge lens and windows became very useful optical components for IR thermal imaging and pyrometry applications.
Ø Ge is diamond turnable, to make advanced Aspherical lens.
Ø EMI grade Ge windows are used for shielding noise signals in modern military applications.
Ø Ge is used to manufacture Attenuated Total Reflection (ATR) prisms for spectroscopy application, due to its high refractive index and stable chemical properties.
Ø The Knoop Hardness of Ge is approximately twice of Magnesium Fluoride, and can be AR coated with Diamond, making it ideal for IR applications requiring rugged optics.
Ø Ge is also common substrate material for detector windows, IR polarizers and filters,
Note: Germanium is subject to thermal runaway, meaning that its transmission decreases as temperature increase, Ge optics usually are not used under temperatures higher than 100℃. Germanium’s high density(5.323g/cm³) should be also considered when designing for weight-restricted systems.
Spherical lens, Aspherical lens, Diffractive aspher
Prisms, ATR prisms, Wedges
Filters for IR detectors
Other customs optics
OPTICAL PROPERTIES ( @ 10.6μm )
Bulk Absorption Coefficient < 0.03/cm
Refractive Index 4.0028
Temperature change of Refractive Index 390 ×10-6 /℃
Thermal Conductivity at 20°C 0.59 W /cm/°C
Specific Heat 0.31 J /g/°C
Linear Expansion Coefficient @ 20°C 5.7 ×10-6/°C
Youngs Modulus 102.7 GPa
Rupture Modulus 93 Mpa
Knoop Hardness 780 Kg/ mm²
Poisson Ratio 0.28
Density 5.323 g/cm³