Hard X-ray free-electron lasers (XFELs) have delivered intense, ultrashort X-ray pulses for over a decade. One of the most promising applications of XFELs is in biology, where researchers can capture images down to the atomic scale even before the radiation damage destroys the sample. In physics and chemistry, these X-rays can also shed light on the fastest processes occurring in nature with a shutter speed lasting only one femtosecond—equivalent to a millionth of a billionth of a second.
Source:
https://phys.org/news/2021-01-clocking-electron-movements-atom.html