Imaging Ultrafast Dynamical Diffraction Wave Fronts in Strained Si with Coherent X Rays

A. Rodriguez-Fernandez; A. Diaz; A. H. S. Iyer; M. Verezhak; K. Wakonig; M. H. Colliander; D. Carbone

Physical Review Letters 127 (2021) 157402-157402

Dynamical diffraction effects in thin single crystals produce highly monochromatic parallel x-ray beams with a mutual separation of a few microns and a time delay of a few femtoseconds—the so-called echoes. This ultrafast diffraction effect is used at X-Ray Free Electron Lasers in self-seeding schemes to improve beam monochromaticity. Here, we present a coherent x-ray imaging measurement of echoes from Si crystals and demonstrate that a small surface strain can be used to tune their temporal delay. These results represent a first step toward the ambitious goal of strain tailoring new x-ray optics and, conversely, open up the possibility of using ultrafast dynamical diffraction effects to study strain in materials.