Development of a narrowband multilayer mirror for extracting a single order component from high harmonics in the 63–70 eV region

The Y/AlSi multilayer with narrowband performance was developed for extracting a single order component from high harmonics. We compared the performance and thermal stability of Y/AlSi with another EUV mirror, Zr/AlSi multilayer, which has shown promising performance in the EUV region. At near-normal incidence, the measured peak reflectances of Y/AlSi and Zr/AlSi multilayers are 43% and 52% at ∼63.8eV, and the energy bandwidths (FWHM) are 1.7 eV and 2.5 eV, respectively. The narrower bandwidth feature obtained in the Y/AlSi multilayer allows better suppression on adjacent high harmonic lines. After heating up to 200°C, there is no significant decrease in the reflectance of either multilayer. No decrease in reflectivity was observed after storage in air for one year.