Each successive generation of X-ray machines has opened up new frontiers in science,
such as the first radiographs and the determination of the structure of DNA. State-of-the-art X-
ray sources can now produce coherent high-brightness X-rays of greater than
kiloelectronvolt energy and promise a new revolution in imaging complex systems on
nanometre and femtosecond scales. Despite the demand, only a few dedicated synchrotron
facilities exist worldwide, in part because of the size and cost of conventional (accelerator) …

This paper presents the realization and comprehensive characterization of a compact bright
source of ultrafast synchrotron radiation with appreciable degree of spatial coherence. It has
been drawn to our attention that we had inadvertently neglected to cite some prior works that
described selected aspects of the betatron radiation in similar experimental configurations:
ref. 1 describes a direct source size measurement based on Fresnel diffraction from laser-
based synchrotron radiation demonstrating the resolution that this measurement can yield …