The coating is physically or chemically coated with a transparent electrolyte membrane on the surface of the material, or a metal film is applied to change the reflective and transmissive properties of the surface of the material.

In the visible and infrared bands, the reflectivity of most metals can reach 78% to 98%, but not higher than 98%. Whether it is for CO2 laser, copper, molybdenum, silicon, germanium, etc. are used to make mirrors, using germanium, gallium arsenide, zinc selenide as output window and transmissive optical component material, or ordinary optical glass as mirror for YAG laser. The output mirror and the transmissive optical component materials cannot meet the requirements of more than 99% of the total reflection mirror. The output mirrors have different transmittance requirements for different applications, so optical coating methods must be used.

For the infrared band in the CO2 laser lamp, the commonly used coating materials are barium fluoride, barium fluoride, barium, etc. For the near-infrared band or visible light band of the YAG laser lamp, the commonly used coating materials are zinc sulfide, magnesium fluoride, titanium dioxide, and oxidation. Zirconium and the like. In addition to high-reflection film and anti-reflection film, it is also possible to plate a special film that enhances reflection at one wavelength and transmits transmission to another wavelength, such as a spectral film in laser frequency doubling technology.