Understanding ultrafast x-ray 'echoes' diffracted from single crystals

TL;DR

This paper demonstrates imaging of ultrafast x-ray diffraction echoes from single crystals with nanometer resolution, revealing potential applications in ultrafast x-ray optics and dynamic process observation.

Contribution

It provides the first detailed imaging and analysis of x-ray diffraction echoes related to the Pendelloesung effect in perfect crystals.

Findings

Observed 10 echo maxima with 78 μm total signal length

Achieved ~100 nm spatial resolution in imaging

Detected a temporal delay of less than 108 fs in echoes

Abstract

Multiple x-ray beams generated by interference processes in perfect crystals were imaged with a resolution of about 100nm using tele-ptychography in the diffraction direction. These multiple wave-fields, also known as x-ray diffraction echoes, are related to the process known as the Pendelloesung effect and are described by dynamical diffraction theory. The echoes are produced by the constructive interference of diffracted x-rays at the exit surface of the crystal sample. In the imaged diffraction peak, we observed 10 echoes maxima with a total signal length of 78 um. Which translates into a total temporal delay in the signal of less than 108 fs.This makes the echoes of high importance for x-ray optics at x-ray Free Electron Laser sources, as the effect could be used for future ultrafast x-ray beam splitters. In addition to this application, echoes can be exploited to follow ultrafast processes in single crystal micro-structures such as melting or strain propagation.