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Germanium
Germanium

   Germanium is used widely for lenses and windows in thermal imaging and FLIR applications. Its high index of refraction (about 4) makes it of particular interest. Useful transmission range of Germanium windows is from 2 to 13mkm. Germanium is opaque in the visible. Germanium has the property of thermal runaway, meaning that the transmission decreases as temperature increases. As such, Germanium window should 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) should 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 8-12µm (BBAR coating or DLC/BBAR) depending on your custom application.

Germanium properties

Chemical Formula

Ge

Crystal Form

Poly or Single Crystal

Crystal Class

Cubic

Resistivity, Ohm*cm

5-40

Lattice Constant, Å

5.66

Molecular Weight

72.60

Density, g/cm3 at 300 K

5.33

Dielectric Constant for 9.37 x 109 Hz at 300 K

16.6

Melting Temperature, K

1210

Thermal Conductivity, W/(m K) at 293 K

59

Thermal Expansion, 1/K at 298 K

6.1 x 10-6

Specific Heat, cal/(g K) at 273-373 K

0.074

Debye Temperature, K

370

Bandgap, eV

0.67

Solubility in water

None

Knoop Hardness, kg/mm2

800

Mohs Hardness

6.3

Young's Modulus, GPa

102.66

Shear Modulus, GPa

67.04

Bulk Modulus, GPa

77.86

Poisson's Ratio

0.278

Refractive index of Germanium

µm   

No

µm   

No

µm   

No

2.058   

4.102

2.153   

4.0919

2.313   

4.0786

2.437   

4.0708

2.577   

4.0609

2.714   

4.0562

2.998   

4.0452

3.303   

4.0369

4.258   

4.0216

4.866   

4.017

6.238   

4.0094

8.660   

4.0043

9.720   

4.0034

11.04   

4.0026

12.00   

4.0023

13.02   

4.0021

 

 

 

 

 

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