Revealing Nanostructure and Density Variations in Polymer Foams for Inertial Fusion Energy

Polymer foams are essential components in modern inertial fusion energy (IFE) target designs, where they improve energy yield and aid in controlling implosion dynamics. However, the absence of high-resolution structural characterization has slowed progress in advancing fusion target designs. We present a high-resolution 3D reconstruction of a low-density, silicon-doped polymer foam produced via two-photon polymerization, imaged using ptychographic x-ray computed tomography (PXCT) at an x-ray free electron laser (XFEL). This technique reconstructs both attenuation and phase information across multiple sample orientations to create a 3D electron density map, from which local mass density and structural features are quantified. We report a 2D spatial resolution of 19 ± 3 nm on a high-contrast Ronchi pattern and 78.7 ± 3 nm for low-contrast polymer foams—demonstrating substantial progress in XFEL-based ptychography for low-density materials. Our analysis reveals an average foam strut thickness of 1.17 ± 0.4 microns and an average reconstructed mass density of 0.35 g/cc, both in good agreement with fabrication predictions. These results offer valuable information for improving foam manufacturing and advancing radiation hydrodynamics models in future IFE studies.