The laser-driven plasma x-ray source (PXS) produces Cu K-alpha radiation (hard x-rays) with a pulse duration of ~200 fs by focussing a femtosecond laser pulse onto a moving copper tape. The generated x-ray pulses pulses are focussed onto the sample of interest mounted in a cryogenic 2-circle goniometer. The x-ray photons diffracted off the sample are detected with a Pilatus 100k pixel detector (DECTRIS) to record time-resolved reciprocal space maps (RSM) or reciprocal space slices (RSS).
The ultrafast strain dynamics of the investigated heterostructures are then derived from time-dependent shifts of various Bragg peaks in reciprocal space, that are material specific probes of the ultrafast lattice changes in each layer. Unlike optical probes, x-rays are capable of detecting layers burried below thick metallic films and even separating the response of two adjacent few-nanometer thick metal layers. The example shown in the right figure displays the rich lattice dynamics inside a heterostructure containing the magnetic rare-earth element Dysprosium which expands upon ultrafast laser-heating at room temperature, but contracts upon excitation at low temperatures due to additional stress components in the magnetic phases.
Reppert et al., Struct. Dyn. 3, 054302 (2016).
Reppert et al., Struct. Dyn. 7, 024303 (2020).