Metal oxide thin films for precision optics in the DUV spectral range

DUV laser applications require optical coatings with minimal optical losses due to scattering and absorption. Consequently, it is necessary to choose the coating materials very carefully. In general, MgF2 and LaF3 are used as materials for 193nm coating designs, deposited by electron beam or metal boat evaporation. But due to high interface roughness, high scattering losses can be observed. Indeed, this problem can be solved by using a plasma assisted deposition process but at the expense of higher absorption losses. However, metal oxides can also be used as coating material for DUV applications. This paper will demonstrate that optical coatings for 266nm, 248nm, and 193nm can successfully produced by using ion beam sputtering technology. This deposition method guarantees coatings with smooth interfaces and significantly lower scattering losses. Due to the optimization of the deposition parameters as well as the post-deposition treatment, coatings with low absorption losses can be realised. In this study, single layers of SiO2, Al2O3, and HfO2 as well as antireflection and high reflection coatings were prepared. The mechanical and optical properties were examined and discussed.