Narrowband Mg/SiC multilayer mirror working as high-harmonic selector at 30.4 nm wavelength

Abstract Multilayers are a good choice for high-harmonic generation sources for selecting single-wavelength radiation. Multilayers working around 30.4 nm with a significantly reduced bandwidth based on high Bragg order reflection have been designed and fabricated. The narrowband multilayers were characterized using grazing incidence X-ray reflectometry, EUV reflectivity, and intrinsic stress measurements. The results indicate that Mg/SiC multilayers designed with 3rd Bragg order have narrowest bandwidth of 0.71 nm (full width half maximum) with a spectral resolution (λ∕Δλ) of 42, and reflectance of 30% under near normal incidence geometry. Based on these results, the simulation of narrowband multilayers working at large incident angles demonstrates that 3rd Bragg order multilayer has a better spectral selectivity compared with 1st Bragg order multilayer for high harmonic generation sources.