The revolutionary large-scale experimental pump-probe platforms equipped with both optical high power lasers and brilliant X-ray free electron lasers (XFELs), such as European XFEL-HED/HiBEF, LCLS-MEC and SACLA beamlines, are opening a new era to investigate the high energy density physics and strong-field quantum electrodynamics (QED) by acquiring the data with fast rate and unprecedented quality. Here, we will present our recent experimental results to investigate the relativistic plasma dynamics in a micro-Cu wire target driven by a 3J/30fs/100 TW laser performed at European XFEL-HED/HiBEF station. Particularly, by fielding the X-ray diagnostics of resonant X-ray emission spectroscopy (XES), we are able to investigate the ultra-fast atomic processes such as ionization and recombination dynamics for a selected highly ionized charge state of Cu with a lifetime of up to $\sim$10 ps in a solid density plasma. Furthermore, a spherical divergent shock originating from the interaction region directly driven by the laser ablation, and a cylindrical convergent shock originated from the wire edges beyond 100 $\mum$ off the focal position driven by the lateral transient surface return current, are clearly observed from 10s of ps to 1 ns using the X-ray phase contrast imaging (XPCI). Such cylindrical shock wave travels towards the wire core and is predicted to reach a compression factor of 9 and pressures nearly 1 Gbar (100 TPa) by the Joule-class femtosecond pulse laser laser, offering an alternative to the nanosecond kJ laser pulse-driven and pulse power Z-pinch compression methods to study the high-pressure physics. The combination of techniques constitute a promising avenue to enable deeper insights into benchmarking the simulation codes and understanding laser-driven ion acceleration, planetary science and fusion energy research.

Relativistic laser plasma physics; Surface harmonics generation; Attosecond pulse; Orbital angular momentum,XFEL,Relativistic Intensity