Germanium
Germanium (Ge) is in the range of 2-12 μm. Germanium is the most commonly used for making optical lenses and optical windows in high-efficiency infrared imaging systems. Due to the wide transmission range and opacity of visible light, Germanium is very suitable for infrared lasers and optical systems for the manufacture of optical components. Germanium's high refractive index and minimal surface curvature make it an ideal material for making low-power imaging systems. The small color difference often eliminates the need for correction.