Ion Beam Sputter Deposition Of Optical Coatings

A beam of 500 to 1200 eV argon and oxygen ions, neutralized with an equal number of electrons, strikes a target, and the sputtered particles form a deposited layer of SiO2, Ta205, or TiO2. A second beam at lower energy is aimed at the substrate and used for stress modification and predeposition sputter cleaning. Deposited films are mechanically stable and extremely adherent; internal stress is compressive. The primary contaminant is carbon, which is less than one percent. Refractive indices near 1 µm are 1.47 for SiO2, 2.03 for Ta205, and 2.27 for Ti02. Optical absorptance of half-wavelength films at 1.06 Am is near 10-4 for SiO2 and Ta205 and near 4 X 10-4 for TiO2. Damage tests with a 114 um radius, 5 ns pulse length, 1.06 um wavelength laser show an onset energy flux for visible damage in the 12 to 30 J/cm2 range for single-layer films, and slightly less for a three-layer structure.