The working wavelength range of germanium (Ge) material is from 2.0 μ m to 16.0 μ m band. The refractive index of germanium material is very high (about 4.0 in the 2-14 μ m band). When used as window glass, it can be coated as needed to improve the transmittance of the corresponding band. Germanium material has a wide spectral range of infrared transmission, making it very suitable for infrared laser applications. The opaque properties of germanium in the visible light range also enable the material to be used as a long wave pass filter.