When light passes through multilayer media, reflection and transmission will occur at the interface of each medium. When the thickness of mutilayer media film meets certain requirements, that is, when the reflected light meets the mutual interference, great rflectivity can be achieved. Generally, metals have large extinction coficient. When the light beam is incident to the metal surface from the air, the light amplitude into the metal rapidly attenuates, so that the light into the metal interior decreases correspondingly, while the reflected light inereases. The larger the extinction coefficient is, the faster the light amplitude decays, and the less light energy enters the metal, the higher the reflectivity. People always choose the metal with high lIght coefficient and stable optical property as the metal membrane material. In the ultravlolet region commonly used metal thin material is aluminum, in the visible region commonly used aluminum and silver, in the infrared region commonly used gold, silver and copper, in addition, chromium and platinum also often make some special film membrane material. When a beam of light passes through the surface of optical equipment, AR film can reduce the reflection, while HR ftim can increase the reflectivity of some wavelengths. Common HR film includes: medium high reflection film and metal high reflection film.