The optical elements made of germanium are convenient to manufacture and operate. They do not interact with atmospheric moisture, are not toxic, durable, and have good thermophysical properties.
Ge has a high hardness, which allows you to form high precision optical parts that are well cleared up even with single layer ZnS or As2S2 coatings.
Ge is used to make translucent mirrors that work with and without interference coatings
Ge optical single crystals are grown in furnaces using the Czochralski method and the horizontal directional crystallization method.