Editing Mirror (section)

====Dielectric coating====
Applications requiring higher reflectivity or greater durability, where wide [[bandwidth (signal processing)|bandwidth]] is not essential, use [[dielectric mirror|dielectric coatings]], which can achieve reflectivities as high as 99.997% over a limited range of wavelengths. Because they are often chemically stable and do not conduct electricity, dielectric coatings are almost always applied by methods of vacuum deposition, and most commonly by evaporation deposition. Because the coatings are usually transparent, absorption losses are negligible. Unlike with metals, the reflectivity of the individual dielectric-coatings is a function of [[Snell's law]] known as the [[Fresnel equations]], determined by the difference in [[refractive index]] between layers. Therefore, the thickness and index of the coatings can be adjusted to be centered on any wavelength. Vacuum deposition can be achieved in a number of ways, including sputtering, evaporation deposition, arc deposition, reactive-gas deposition, and ion plating, among many others.<ref name=pulk1999/>{{rp|p.103,107}}