Germanium Window

Germanium is widely used for lenses and windows in thermal imaging, LWIR applications, as germanium viewports. Its high index of refraction (above 4) makes it of popular among application engineers.

Useful transmission range of Germanium windows is from 2 to 13µm. Germanium is opaque in the visible. Germanium has the property of thermal runaway, meaning that the transmission decreases as temperature increases. As a caution, Germanium windows can only be used at temperatures below 100°C.

The Knoop Hardness of Germanium (780) is approximately twice that of Magnesium Fluoride, making it ideal for IR applications requiring rugged optics. Germanium’s high density (5.33 g/cm^3) needs to be considered when designing for weight-sensitive systems.
Custom Germanium windows and Germanium lenses are available in any size and configuration. Anti-reflection coatings can be applied for 2-14µm or 8-12 µm (BBAR coating or DLC /BBAR) depending on different applications.
Factory Standard – Contact us for manufacturing limit or custom specifications.

  • Germanium  Window  with different sizes (2 mm – 100 mm)
  • Diameter: +0/-0.05 mm
  • Thickness: +0.01/-0.03 mm
  • Flatness: 1/2 Lambda
  • Parallelism: < 3 arc min
  • Polished surface finish:20-10 (no dig)
  • Bevel: protective bevel
  • Transmission rate: >47.5%@3.7-4.8um or according to customer’s specifications


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