An EUV beamsplitter based on conical grazing incidence diffraction

We present an innovative grating design based on conical diffraction which acts as an almost perfect and low-loss beamsplitter for extreme ultraviolet radiation. The scheme is based on a binary profile operated in grazing incidence along the grating bars under total external reflection. It is shown that periods of a few 102 nm may permit an exclusive (±1)st order diffraction with efficiencies up to ~ 35% in each of them, whereas higher evanescent orders vanish. In contrast, destructive interference eliminates the 0th order. For a sample made of SiO2 on silicon, measured data and simulated results from rigorous coupled wave analysis procedures are given.