High‐energy resolution in x‐ray scattering for inelastic studies of excitations in condensed matter

Very‐high‐energy resolution measurements using x rays can be achieved by extreme backreflection (Bragg angle close to 90°) from perfect crystals. This technique, combined with the high intensity of x rays emitted by the HARWI wiggler at DORIS, DESY Hamburg, allowed the development of the instrument INELAX for inelastic scattering experiments. Recently, the high‐energy resolution of 9 meV could be achieved and the instrument proved to be an excellent tool to investigate collective excitations in condensed matter. Energy transfers from 10 meV to 5 eV and wavevectors over the whole reciprocal space are accessible