Design and theoretical investigation of nanograting for XUV outcoupler

摘要

We have theoretically investigated and optimized a nano-periodical highly-efficient blazed grating, which is used as an outcoupler for extreme-ultraviolet (XUV) radiation. The rigorous coupled-wave analysis (RCWA) with S matrix method is employed to optimize the parameters of the grating. The grating is designed to be etched on top layers of IR reflector, performs as a highly-reflective mirror for IR light and highly-efficient outcoulper for XUV. The diffraction efficiency of-1 order of this XUV outcoupler is greater than 20% in the range near 60 nm, which allows high resolution spectroscopy of the 1s-2s transition in He~+ at around 60 nm with extreme precision. The theoretical calculations are verified by the experimental results.