Silicon (Si) single crystal is a chemically inert material with high hardness and insoluble in water. It has good transmittance in the 1.2 -7um band, and it also has good transmittance at the far infrared band of 30-300 mu m, which is the feature that other infrared materials do not possess. Silicon (Si) single crystal is usually used as the substrate of 3-5? M medium wave infrared optical window and optical filter. Because of its good thermal conductivity and low density, it is often used for making laser mirrors and sensitive to volume and weight. The silicon lens or window produced by our company is the optical level silicon single crystal. The diameter range is: 5~260mm, the surface precision is usually up to 40/20, the surface roughness is up to: lambda /10@633nm (the ratio of the thickness to diameter of the lens needs to be proportional to the processing ratio).