Design, manufacturing, and characterization of multilayer mirrors based on magnetron sputtered quantized nanolaminates

Quantized nanolaminates (QNL) are a new type of metamaterials proposed only recently. The basic properties of QNL single layers have been investigated for various material combinations and deposition techniques. Based on these results the hypothesis was put forward that, thanks to the blueshift of the absorption edge, multilayer interference filters composed of QNL-SiO₂ will lead to an increased laser damage threshold in the femtosecond regime compared to standard coatings of the same material combination. In our work we will show a comparison of mirrors with and without QNL designed for the wavelength of 1030nm. For these coatings both standard Ta₂O₅ and SiO₂-Ta₂O₅ QNL were used as high and SiO₂ as low refractive index material. Mirrors consisting of Ta2₂O₅ and SiO₂ without QNL were also deposited for reference. The designs used were either quarter-wave designs or designs aiming at reducing the electric field. A magnetron sputter system with a rotating table was used for depositing the multilayer designs. The design of the tool allows to deposit a Ta₂O₅/SiO₂ layer pair at every rotation of the table, which results in a QNL deposition rate higher than the rate for the individual materials. In order to accurately terminate the layers at the design thicknesses, broadband optical monitoring was used. Subsequently, the coatings were investigated by spectrophotometry and femtosecond laser induced damage threshold (LIDT) measurements at 1030nm. These measurements showed that samples with QNL exhibit an improved damage threshold compared to standard high-low mirrors as well as to a commercial ion beam coated fs-mirror. Furthermore, it is shown that the designs with optimized electric field exhibit higher LIDT values than their standard λ/4 design counterparts.