Toward Photon-Induced Near-Field Electron Tomography

New techniques for imaging electromagnetic near-fields in nanostructures drive advancements in nanotechnology, optoelectronics, materials science, and biochemistry. Most existing techniques probe near-fields along surfaces, lacking the ability to extract near-fields confined within the structure. Notable exceptions use free electrons to traverse through nanostructures, integrating the field along their trajectories, extracting 2D near-field projections rather than the complete field. Here, drawing inspiration from computed tomography (CT), we present a tomography concept providing full 3D reconstruction of vectorial time-harmonic near-fields. We develop a Radon-like algorithm incorporating the electron wave-nature and the time dependency of its interaction with vector fields. To show the prospects of electron near-field tomography, we propose and analyze its ability to resolve the sub-wavelength zigzag profile of highly confined hyperbolic polaritons and to reconstruct 3D phase singularities in a chiral near-field, raising exciting goals for next-generation experiments in ultrafast transmission electron microscopes.