Investigations of large x-ray optics for free electron lasers

A free electron laser (FEL) is being set up at DESY (Deutsches Elektronen Synchrotron, Hamburg, Germany). In the current XUV range of the FEL, total-reflection X-ray mirrors are needed for beam guidance, beam alignment, and monochromatisation. Such X-ray optics are used at a grazing incidence angle of about 2°; thus a maximum length of about 500 mm is required. Due to the working range of the FEL (50 - 200 eV), carbon has been selected as a suitable material with an absorption edge at 284 eV. The amorphous carbon coatings were manufactured by magnetron sputtering in a special UHV system for large deposition at GKSS research centre (Geesthacht, Germany). The variation in film thickness over the whole length has been investigated by X-ray reflectometry (XRR). Good uniformity (better than 2 %) and low roughness (< 0.5 nm) have been observed.