Investigation of stresses and optical properties of metal oxide mixture thin films formed by ion beam sputtering technology

New and more complex requirements for multilayer optical coatings are raised due to development of laser technology. Flatness, which is determined by stresses within thin layer of the coating, is one of the important properties of optical components for precise laser systems. Metal oxides mixtures could be possible solution for stress supression, since in this case new material is created with different refractive index and stress properties. Stresses within deposited thin films could also be modified by anealing process. Al2O3-SiO2 mixture with small fraction of alumina could be one of the most perspective combination for SiO2 thin film replacement, since refractive index and extincion coefficient of Al2O3 are relatively small. In this investigation thin films of different volume fraction of Al2O3-SiO2 mixtures are formed using ion beam sputtering technology. Experimental samples were annealed at different temperatures, refractive indices and stresses were evaluated. Study revealed that all mixtures had smaller compressive stresses comparing to pure Al2O3 and SiO2 materials after anealing at 300C temperature. Annealing to even higher temperatures has resulted in tensile stresses for all mixtures. Refractive index has also decreased after anealing for all different Al2O3-SiO2 mixtures. Investigation showed that mixture of 8% Al2O3 volume fraction and SiO2 could successfully replace pure SiO2 layers within the multilayer optical mirrors, where stresses should be compensated