Attosecond hard X-ray pulses at an X-ray free-electron laser: average duration measured at 170 as
Authors established metrology of attosecond hard X-ray pulses and measured their average duration directly in the time domain. This removes a limit on attosecond X-ray experiments.
A study in Nature reports metrology of attosecond hard X-ray pulses generated at X-ray free-electron laser sources. Intensity autocorrelation measured directly in the time domain gives an average pulse duration of 170 attoseconds nature.com
Naturenature.comOpen source ↗. The work builds on a broadband X-ray split-delay line, which produces pairs of pulses with a controlled delay.
Why pulse metrology was needed
Sub-ångström spatial resolution combined with attosecond temporal resolution makes it possible to observe electron motion in matter directly, the authors write. Attosecond hard X-ray pulses from X-ray free-electron lasers provide the required spatiotemporal sensitivity. Their use, however, has been limited by the absence of precise pulse metrology and control.
What was measured
Field-correlation measurements gave the first time-domain characterization of the pulse coherence time. The same measurements demonstrated attosecond synchronization between the generated pulse pairs. These two results characterize the pulses and show that the delay between the pair members is controlled at the attosecond scale.
For the duration, the authors used non-sequential two-photon absorption as a nonlinear probe. Intensity autocorrelation based on this process quantifies the average pulse duration directly in the time domain, and the value obtained is 170 as nature.com
Naturenature.comOpen source ↗. The figure is an average over pulses, as reported by the authors.
Intended applications
The authors state that the demonstrated experimental tools and techniques enable systematic attosecond time-resolved experiments. They name X-ray pump–X-ray probe spectroscopy and diffraction among them. According to the authors, the approach opens a pathway to probing electronic phenomena with unprecedented spatial-temporal resolution.
The available material is the abstract of the paper; the full text is behind a subscription. Details of the facility, the instrument parameters and the measurement statistics are therefore not covered here.
