Germanium lenses are mostly used in aerospace and defense systems as well as in medical technology and general infrared measurement technology. Germanium optics can be used very well as lenses or windows. With an additional, perfectly matched multilayer coating, they also function as pass or band filters;
Thermodynamic restrictions
The optical properties of germanium are significantly influenced by the temperature. As the transmission decreases with increasing temperature, germanium optics can only be used at temperatures below 100°C.
Versatile use due to high robustness
Germanium is always used when robust optics are required. It is extremely hard (Knoop hardness of ~ 780) and has a density of 5.33 g/cm³. In addition, germanium does not react with air, water, bases and many acids, which makes this material very versatile.