The European XFEL generates extremely short and intense x-ray laser pulses, with high coherence and diffraction-limited divergence. It generates ultrashort x-ray ashes, 27000 times per second, with a brilliance that is a billion times higher than that of the best conventional x-ray radiation sources. Due to these extreme beam characteristics, the x-ray mirrors to transport and focus the beam need to be coated to protect them against beam damage. The surface quality of these mirrors before the coating is in the order of 2nm peak-to-valley and 200km radius on average. The ultra- at x-ray mirrors of ultimate precision are important in order to preserve the quality of the beam delivered to the experiments and the coating must not compromise the surface quality. This manuscript presents a preliminary study of the surface quality of 2 mirrors that will be part of the Optical Delay Line (ODL) before and after coating using Fizeau and White Light Interferometry.
Martín et al. (Mon,) studied this question.