metallic mirror coatings
The reflection properties of metallic coatings depend on wavelength, polarization state and angle of incidence. In addition, metallic coatings may act as polarization rotator and phase shift the E vector orientation. Materials used for metallic mirror coatings are aluminum, silver and gold. According to the kind of metal and wavelength range, the reflection level is from 85 % to 98 %. Because of significant absorption level of metallic layers, such kind of mirrors cannot be used in systems where high light power density is present. Coatings made of evaporated metals are chemically sensitive and can function as oxidizers. Therefore they are given an additional coat of SiO2 or MgF2 as protection layer, due to the wavelength range demanded. For UV and VIS there is used MgF2 and for VIS and NIR it is used SiO2. For laboratory use there can be also produced aluminum mirrors without protection .
Gold mirrors can be also made with or without protection layer.