Coating method for variable reflectivity mirrors to be used in high power CW CO2 lasers

The design of a variable reflectivity mirror (VRM) is reported, according to the requirements imposed on the output coupler of an U-type resonator for an industrial, CW, transverse flow CO2 laser. The reported method consists of building a variable thickness layer of BaF2 on GaAs substrate material using RF magnetron sputtering coating. The obtained VRM final structure is air-(ZnS)/GaAs/(BaF2, ZnSe)-air exhibiting a maximum reflectivity of the central zone, at 10.6 mu m, between 66% and 69%. The component worked, mounted on the laser resonator, for more than 600 h allowing a single mode beam structure at power levels between 800 W and 1 kW CW.