High-resolution characterization of HED shock dynamics in laser-irradiated foams: implementing advanced x-ray phase-contrast methods at the LCLS-MEC*

Shock dynamics play a profound role in the behavior of matter in extreme conditions. The advent of high-intensity laser facilities enables experimental platforms for fundamental plasma studies in new regimes where probing highly dense matter with sub-µm, -ns variations is a challenge. Hence, novel x-ray phase-contrast methods were implemented at LCLS-MEC leveraging XFEL beams. 2D Talbot X-ray interferometry probed dynamic compression (60J, 10ns, >10¹⁵ W/cm²) in porous media. Little is known about foam microphysics thus, standard and additively manufactured (AM) targets explored density and structure impact on shocks. Talbot provided simultaneous phase, transmission, and darkfield with remarkable resolution (<500nm, ~300fs). Shocked material density distribution indicates instabilities are predominant for lower density foams. Simulation can determine the extent to which radiation and hydrodynamics are relevant in the description of these shocks. With high sensitivity, Talbot revealed features not observed in x-ray phase-contrast images (XPCI). Even at LCLS, precise areal density had not been determined for large mesoscale samples due to shot-to-shot noise and low XPCI contrast. Notably, Talbot is robust against intensity variations, separating phase contributions instrumentally and advanced Talbot methods allow for wavefront reconstruction. Average shock velocity was inferred from velocimetry: 7 and 25km/s for 500 and 20mg/cc standard foams, and 23 and 37km/s were determined from Talbot images. This discrepancy is more pronounced for slower shocks (denser foams), consistent with deceleration observed post laser driver. 2D phase maps of AM targets suggest 3D printed structures dominate dynamics and may provide reliable means to control shock propagation and instability onset and growth. Combined with unique Talbot capabilities, the LCLS-MEC shock platform is suitable for compressed materials studies, providing valuable data not available from other HED facilities, serving as strategic testbed for target studies with high interest in IFE (e.g., Two-Photon Polymerization structures, wetted, and metallic foams), planetary and materials science, and beyond. LA-UR-24-26558