# Attosecond hard X-ray pulses at an X-ray free-electron laser: average duration measured at 170 as

- Published: 2026-11-05 23:03 UTC
- Section: Science › Instruments & experiments
- Tags: attosecond hard X-ray pulses, X-ray free-electron laser, X-ray split-delay line, pulse duration 170 as, intensity autocorrelation, non-sequential two-photon absorption, coherence time, X-ray pump–X-ray probe, attosecond metrology
- URL: https://realtech.media/news/rt-cf63cb8926545431d15c0993_attosecond_hard_x/

**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.**

![Attosecond hard X-ray pulses at an X-ray free-electron laser: average duration measured at 170 as](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/53cb87942afa4d94.png)
*Nature*

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 [1]. The work builds on a broadband X-ray split-delay line, which produces pairs of pulses with a controlled delay [1].

## 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 [1]. 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 [1].

## What was measured

Field-correlation measurements gave the first time-domain characterization of the pulse coherence time [1]. The same measurements demonstrated attosecond synchronization between the generated pulse pairs [1]. 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 [1]. 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 [1]. According to the authors, the approach opens a pathway to probing electronic phenomena with unprecedented spatial-temporal resolution [1].

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.

## Sources

1. [Nature](https://doi.org/10.1038/s41586-026-11245-5)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-cf63cb8926545431d15c0993_attosecond_hard_x/