Design of novel titanium oxide/zinc oxide multilayer mirror for attosecond soft X-rays

A novel attosecond multilayer mirror was designed at 'water-window' wavelengths (from 2.33 nm to 4.36 nm) using a combination of TiO2 and ZnO, because both rutile TiO2 and wurtzite ZnO can be grown epitaxially together on the same c-plane sapphire substrate in spite of the different crystal structures of the molecule hexagonal units of rutile TiO2, wurtzite ZnO and sapphire. The theoretical calculation of the TiO2/ZnO multilayer mirror indicated that a high reflectivity of 50% was attainable at 2.73 nm and at an incident angle of 17.35 deg. from normal incidence. Moreover, it also indicated that a simple 3-block structure could exhibit a reflectivity of about 15% for a 480-attosecond pulse at a water-window wavelength and thus could be used to control the phase relation.