Access to nanosecond and microsecond dynamics is essential for understanding structural evolution in complex systems, ranging from protein function, diffusion in solids and liquids, to phase transformations and energy transport in batteries. Conventional two-dimensional X-ray detectors cannot continuously record coherent scattering patterns at such speeds because data volumes exceed current transfer capabilities. Burst-mode operation partially addresses this challenge by capturing a limited number of frames within microseconds, but its low duty cycle restricts its applicability to strongly scattering samples.
A new solution has been demonstrated with the TEMPUS prototype detector [1], developed at DESY and based on the Timepix4 chip [2] from the CERN-led Medipix4 Collaboration. In event-driven mode, the detector transmits data packets only when individual pixels register photon hits, each tagged with a sub-nanosecond timestamp. This approach supports 1.28 billion photon events per second per chip, fundamentally changing the way high-speed X-ray measurements can be performed [2].
At ID10, this mode provides nanosecond-scale time resolution for XPCS. Unlike conventional detectors limited by frame rates, TEMPUS delivers continuous photon arrival-time traces per pixel. In recent work, researchers utilised this mode to measure diffusion in colloidal suspensions with nanosecond sensitivity (see the Principal publication).
In XPCS, temporal speckle intensity fluctuations arising from particle motion are quantified via autocorrelation functions. For per-pixel autocorrelations, the shortest accessible time is limited not by frame rate but by pixel dead time (typically hundreds of nanoseconds, as shown in Figure 1a). By exploiting cross-correlations between neighbouring pixels (Figure 1b), effective time scales down to ~10 ns become accessible, albeit with reduced contrast.
Fig. 1: Measured intensity correlation functions. (a) Temporal intensity autocorrelation functions together with the fits (grey dashed lines). (b) Temporal intensity cross-correlation functions with the fits (grey dashed lines).
This capability bridges the gap between neutron spin-echo and conventional XPCS techniques, establishing a new regime for investigating ultrafast nanoscale dynamics. By overcoming the trade-offs between duty cycle and time resolution, it enables efficient access to nanosecond-to-microsecond processes at ID10, significantly extending the range of experiments possible with the ESRF-EBS source.
Event-driven detection thus provides a transformative advance for investigating fast structural and dynamical processes across materials science, soft matter, and biology. Beyond XPCS, potential applications include time-resolved diffraction, scattering, and imaging experiments, where unprecedented temporal resolution could open new scientific frontiers. Tests at ID09, ID14, and ID19 are underway or planned.