Aberration-free and harmonic-free optics for time-resolved X-ray absorption spectroscopy using synchrotron radiation

To obtain aberration-free optics, we tailored a new crystal shape which achieves an ellipsoidal profile. The theoretical shape has been designed using elastic equations and a ray-tracing technique. Cutting has been carried out and evaluation of the on-site performance has been achieved for a set of crystals. The size of the image turns out to be limited only by the demagnification factor and is restricted to about 300 μm. In order to get rid of the harmonics contamination and to get a reliable signal out of an absorbing sample we use a flat fused quartz mirror at grazing incidence as a low-pass filter. The performance of this filter has been studied experimentally by scanning the angle of the mirror relative to the beam and by a ray-tracing simulation. An adjustment of the grazing incident angle to reflect the fundamental without any harmonic contamination turns out to be an efficient and easy task in our current setup. (orig.)