Germanium is most widely used for lenses and windows in IR systems operating in the 1.6 - 18µm range. Its transmission is very temperature sensitive, becoming opaque near 100°C Environment does not cause problems because Germanium is inert, mechanically rugged, and fairly hard.
Safetyrich optical selected high quality material to satisfy with customer different request.

Optical property
Crytal form	Poly or single crystal
Crystal Class	Cubic
Density at 293k ,g/cm3	5.33
Thermal Conductivity  W/(mk)at 293K	59
Thermal Expansion 1K at 298K	6.1X10-6
Lattice Constant,Å	5.66
Molecular Weight	72.60
Dielectric Constant for 9.37x109Hz at 300K	16.6
Melting Point,K	1210
Specific Heat,cal/(gK)at 273-373K	0.074
Debye Temperature,K	370
Knoop Hardness,kg/mm2	800
Young's Modulus,GPa	102.66
Shear Modulus,Gpa	67.04
Bluk Modulus,GPa	77.86
Poisson's Ratio	0.278
Mohs Hardness	6.3
Bandgap,eV	0.67
Water Solubility	None

Refractive Index
Wevelength (µm)	n	Wevelength (µm)	n
2.06	4.10	4.36	4.02
2.15	4.09	6.24	4.01
2.44	4.07	8.66	4.00
2.58	4.06	9.72	4.00
3.00	4.05	11.04	4000
3.42	4.03	13.02	4.00