Opt⚙City ®-Quality Crystal & Optical Components
Germanium is a high index material that is used to manufacture Attenuated Total Reflection (ATR) prisms for spectroscopy. Germanium Crystal refractive index is such high 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 10E-6 /°C (2)(6)
dn/dµ = 0 : Almost constant
Density : 5.33 g/cm³
Melting Point : 936 °C (3)
Thermal Conductivity : 58.61 W m-1 K-1 at 293K (6)
Thermal Expansion : 6.1 x 10E-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
- Germanium crystal's high index is desirable for the design of lenses that might
not otherwise be possible.
- Germanium crystal has nearly the highest density of the IR transmitting materials, a consideration when designing for weight restricted systems.
- Germanium crystal is subject to thermal runaway; the hotter it gets, the more the absorption increases. Pronounced transmission degradation starts at about 100°C and begins rapidly degrading between 200°C and 300°C, resulting in possible catastrophic failure of the optic.
- Germanium crystal is generally less expensive than ZnSe and Cleartran.
- Germanium crystal is diamond turnable.
Typical application: Thermal imaging, FLIR (Forward Looking Infrared)
Products manufactured: Lenses, Aspheric Lenses, Binary (Diffractive) Lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges.
Surface Finish: Typical 40-20 or 60-40 scratch-dig. Diamond Turned 120
Angstroms rms or better.
Surface Flatness: Range from 1/2 wave to 2 waves @633nm depending on the system performance requirements.
AR coating: BBAR for 3 to 5µm, 8 to 12µm, and the 3 to 12µm spectral regions. Other specialized bands are possible from 2 to 12 µm.
OptoCity offer Germanium crystal as large as Dia. 300mm. Germanium manufactured products: Germanium Lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges and other Germanium optical components according to customer's specifications and drawings.
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