Aging and thermal stability of Mg/SiC and Mg/Y₂O₃ reflection multilayers in the 25-35 nm region

Reflection measurements in the 25-35 nm region were made for Mg/SiC and Mg/Y₂O₃ multilayers kept in a low-humidity atmosphere for 4 or 5 years. Aged Mg/SiC multilayers keep their reflectances, and the reflectance value at 31.2 nm is 0.44 at 10° of the normal angle of incidence. Aged Mg/Y₂O₃ multilayers change reflectance as top layer materials, and the best value at 30.1 nm is 0.40 at 10°. Reflection measurements are also made for Mg-based multilayers that are annealed from room temperature to 400°C at 50°C intervals. Both multilayers keep their reflectance at annealing temperatures of 200°C. These results suggest that both Mg-based multilayers can be applied to practical optics.