Probing ultrafast heating and ionization, shock and cylindrical implosion dynamics in ultra-short relativistic laser-wire interactions using an XFEL

Understanding the complex plasma dynamics in ultra-intense relativistic laser–solid interactions is fundamentally important for advancing applications such as laser-plasma-based particle accelerators, the creation of high energy-density matter, and laser-driven inertial fusion energy. However, experimental progress in this regime has been significantly constrained by the challenges of accessing over-critical densities and the limited spatiotemporal resolution of existing diagnostics. Over the last decade, the commissioning of novel experimental pump–probe platforms equipped with both high-power optical lasers and brilliant X-ray free-electron lasers (XFELs)—such as the European XFEL-HED, LCLS-MEC, and SACLA beamlines—has opened new horizons for overcoming these limitations.

In this talk, I will present our recent experimental results on ultrafast heating and ionization, shock formation, and cylindrical implosion dynamics of wires, observed in ultra-intense laser pump–probe experiments conducted at the European XFEL-HED station [1–2]. These studies span spatial scales from nanometers to micrometers and temporal scales from femtoseconds to hundreds of picoseconds [3–4]. The observations are enabled by a novel combination of advanced X-ray diagnostics, including small-angle X-ray scattering (SAXS), resonant X-ray emission spectroscopy (RXES), and various X-ray imaging techniques such as propagation-based phase contrast, direct imaging, and Talbot imaging. The measurements reveal a distinct rise-and-fall temporal evolution of the resonant X-ray emission yield, indicating the underlying heating and ionization dynamics. Furthermore, the attenuation and phase shifts in the hot dense plasma have been successfully reconstructed from the imaging data, enabling direct retrieval of key plasma parameters—such as density maps—to investigate the shock and cylindrical dynamics. Comprehensive atomic collisional-radiative, particle-in-cell, and magneto-hydrodynamic simulations will also be presented to fully interpret our measurements.

[1] L. Huang and T. Kluge, Probing the lateral transport of hot electrons in relativistic laser solid wire target interactions, https://doi.org/10.22003/XFEL.EU-DATA-003129-00 (2022).
[2] L. Huang, HIBEF PA - Probing transient surface return current in relativistic laser solid wire interactions, https://doi.org/10.22003/XFEL.EU-DATA-008042-00 (2025).
[3] A.L. Garcia et.al., Cylindrical compression of thin wires by irradiation with a joule-class short-pulse laser, Nature Communications 15, 7896 (2024).
[4] L. Huang, et.al., Demonstration of full-scale spatio-temporal di- agnostics of solid-density plasmas driven by an ultra-short rel- ativistic laser pulse using an x-ray free-electron laser, arXiv:2505.06425 (2025)