Analysis of challenges and process fidelity of projection two-photon polymerization for inertial fusion energy target fabrication

Two-photon polymerization (2PP) enables the deterministic fabrication of complex inertial fusion energy (IFE) targets with nanoscale precision. Key components for direct-drive schemes include spherical shells, which require high form fidelity and low surface roughness, as well as open-porous foams with precise control over density and pore size distribution. However, the low throughput of conventional point-scanning 2PP limits it to prototype production. Projection two-photon polymerization (P2PP), based on simultaneous spatial and temporal focusing, offers a high-throughput alternative by polymerizing entire layers at once. While high printing speeds have been demonstrated at sub-micron resolution, the capability of this approach to meet the stringent fidelity requirements of IFE targets remains unverified. In this study, we provide a foundational characterization of P2PP for these specific geometries. We establish a correlative metrology workflow, combining scanning electron microscopy, X-ray computed tomography, and confocal laser scanning microscopy with 3D digital-to-physical registration, that lays the foundation for iterative process optimization. Using this framework, we quantify the influencing parameters on strut geometry, analyze internal foam integrity, and evaluate the form and surface roughness of hemispherical shells. We identify illumination inhomogeneity as the dominant source of high surface roughness and fabrication defects. A key contribution of this work is the identification of severe, orientation-dependent voxel anisotropy caused by the 1D diffraction of the digital micromirror device used in the P2PP setup. Inspired by established line scanning techniques in multiphoton microscopy, we explored a line scanning approach within P2PP and, in limited cases, observed a reduction in voxel aspect ratio by about 45 % , relative to full-layer projection, with a strong orientation dependence.