Because of the high hardness of Ge, it is often used in high intensity infrared systems. Because of its high refractive index, we usually coating the Ge film on the surface, which is commonly used by: 3~12um or 8~12um. The transmittance of Ge will decrease with the increase of temperature. Strictly speaking, the temperature of the best application of Ge is under 100 degrees Celsius. When applied to the system with more sensitive weight, the designer should consider the high density characteristic of Ge. The ratio of the size and thickness of the lens should conform to the processing ratio and the weight should meet the design requirements. The diameter range of the Ge lens and window produced by our company is: 5~260mm, the surface precision is up to 20/10, the surface roughness is up to: lambda /10@633nm (the ratio of the thickness to diameter of the lens should be in accordance with the processing ratio).