X-ray stopwatch can measure durations of just attoseconds

Nature, Published online: 04 November 2026; doi:10.1038/d41586-026-03423-2

The duration of short ångström-wavelength X-ray pulses, which lasted merely 170 attoseconds, has finally been measured accurately. The optical system designed for precision pulse duration metrology can be used as a ‘stopwatch’ to measure the rapid motion of electrons inside atoms and molecules, too.