Multiple-order reflections from monochromating crystals for the collection of X-ray absorption spectra at extremely high energies

A simple method to collect X-ray absorption spectra at extremely high energies (greater than or equal to 50 keV) is presented. The method is based on the use of the third harmonic signal from a conventional double-crystal monochromator. Strengths and limitations of the method are shown, together with a few experimental examples on metallic foils and oxide powders in transmission and fluorescence mode.