Germanium(Ge) Window

Germanium (Ge) windows are available off-the-shelf with three anti-reflection coating options: 3 – 5μm for mid-infrared applications, 3 – 12μm for broadband multispectral applications, or 8 – 12μm for thermal imaging applications. Due to its high index of refraction (around 4.0 from 2 – 14μm), an anti-reflection coating is recommended on these germanium windows for sufficient transmission in the region of interest. Germanium is subject to thermal runaway, meaning that the transmission decreases as temperature increases. As such, these germanium windows should be used at temperatures below 100°C. Germanium’s high density (5.33 g/cm3) should be considered when designing for weight-sensitive systems. The Knoop Hardness of germanium (780) is approximately twice that of magnesium fluoride, making it ideal for infrared applications requiring rugged optics.


1 ) Uncoated or with AR Coatings Designed for a Variety of IR Ranges

2 ) Minimal Chromatic Aberration Due to Low Dispersion

3 ) Ideal for Infrared Applications Requiring Rugged Optics


1 ) Diameter: 3~300mm

2 ) Diameter Tolerance: +/-0.2mm

3 ) Thickness Tolerance: +/-0.03mm

4 ) Aperture: >90%

5 ) Surface Quality: 80/50~10/5 (S/D)

6 ) Parallelism: <1 arc minute

7 ) Chamfer: 0.3-0.5mmx45°

8 ) Coating: AR/AR@7-14μm; DLC/AR@7-14μm; BBAR/BBAR@3-12μm

Optical Properties

Transmission Range

1.8 to 23 micron

Refractive Index

4.0026 at 11 micron

Refractive Loss

53% at 11 micron

Crystal/Class Structure

Cubic Diamond, Fd3m

Cleavage Plane


Thermal Properties

Thermal Expansion

6.1×10-6 / ℃ at 298K

Thermal Conductivity

58.61W m-1K-1 at 293K

Melting Point

936 ℃

Specific Heat Capacity

310 J Kg-1K-1

Mechanical Properties


5.33 g/cc


Knoop 780

Youngs Modulus

108.7 GPa

Shear Modulus

67 GPa

Bulk  Modulus

77.2 GPa

Poisson Ratio


Elastic Limit

89.6 MPa(13000psi)

Molecular Weight


Chemical Properties


Insoluble in water

Technical Images