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Germanium (Ge) lenses

  • Maximum diameter 300mm
  • Broad wavelength range covers 3μm to 14μm
  • Fit for both MWIR (3-5micro) and LWIR (8-12 micro)
  • Aspherical surface lenses by SPDT offered
  • Coating options: DLC coating, AR@3-5μm, AR@8-12μm, BBAR@3-12μm and custom
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Materials Optical grade germanium single crystals Diameter Range ~300mm
Diameter Tolerance -0.01/-0.03mm Thickness Tolerance +/-0.03mm
Surface Quality 60/40 S/D Frings (N) 3
Irregularity (delta N) 1 Centration 3'
Chamfer 0.1-0.3mmx45 degree Coatings AR/AR@7-14micro DLC/AR@7-14micro BBAR/BBAR@3-12 micro See coating curves below


Physical and Optical Properties:

Transmission Range 1.8 to 23 μm Refractive Index 4.0026 at 11 μm (1)(2)
Reflection Loss 53% at 11 μm (2 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

Germanium lenses (Ge lenses) are commonly used in IR imaging systems operating in the 2 µm to 16 µm spectral range, covering the LWIR (8-12μm) and MWIR (3-5μm) thermal imaging applications. Germanium has the highest refractive index of commonly available IR-transmitters and has low optical dispersion. This makes it desirable in aspects of lens design where its refractive index allows otherwise impossible specifications to be realized. Germanium can be Diamond or DLC coated to be utilized as the front optics in the lens group with surpassing toughness and reliability. Germanium is more rugged than other IR materials, but caution should be taken for high-temperature conditions where the material will become opaque in the IR realm as the temperature rises. Besides the generally spherical surface lenses, Hangzhou Shalom EO also provides the aspherical surface lenses made by SPDT (Single Point Diamond Turning) technique.

Hangzhou Shalom EO suppliers a series of  Germanium Optical Lenses including plano-convex, plano-concave, double convex, double concave, and meniscus Ge lenses, with the spherical and aspherical lens surface. Coating Options encompass Anti-reflection (AR), Broad Band AR (BBAR), and Diamond (DLC) coatings, which are selectable upon customers' request.

Application Notes:

Germanium (Ge) is a relatively hard, high-density, IR transmitting material that blocks UV and VIS wavelengths but transmits IR spectrum greater than 2µm. Germanium has the highest refractive index of commonly available IR-transmitters and low optical dispersion. The optical transmission rate of Germanium is over 45% between 2-14μm at temperatures up to 45⁰C, but its transmission starts to degrade gradually at 100⁰C, then plummets more rapidly above 200⁰C. Exposure to higher temperatures can lead to catastrophic failure in the material so Germanium is unsuitable for use in high-temperature conditions. Additionally, its relatively high density should be considered where weight is an issue. Germanium has a hardness of HK780, slightly higher than GaAs with which it shares similar mechanical properties.

Common applications for Germanium include thermal imaging where the material can be used as a front optic while its large refractive index makes Germanium useful for wide-angle lenses and microscopes. Additionally, Germanium components can be used for FLIR (Forward Looking Infrared) and FTIR (Fourier Transformed Infrared) spectroscopy systems, alongside other analytical instruments.
To lower the cost and improve the imaging quality of lens assemblies used in thermal imaging cameras, incorporating aspherical lenses in the lens group is a preferable measure. Hangzhou Shalom EO fabricates aspherical Ge lenses made by SPDT (Single Point Diamond Turning) technique.


1.Transmission curve1, transmission of Ge windows with no coating

2. Transmission curve for Ge windows with coating AR/AR of 3mm thickness

3.Transmission curve for Ge windows with coating AR/DLC of 3mm thickness

4. Transmission curve for Ge windows with coating AR/AR of 1mm thickness