Imaging localized field inside metal nanoparticles by photoion spectroscopy

Understanding the optical response of metal nanoparticles under laser irradiation demands precise mapping of their internal electric fields. Although photoion momentum distribution (PIMD) enables external field reconstruction, internal field characterization remains challenging due to ion collision-induced information loss. Here, we integrate molecular dynamics (MD) simulations-accounting for multi-body interactions during ion emission-with ion momentum spectroscopy to establish three quantitative relationships: (1) internal field direction correlates with PIMD asymmetry, (2) peak field intensity aligns with ion yields, and (3) penetration depth links to the FWHM of momentum distributions. Applying these relationships, we reconstruct the internal field distribution in laser-irradiated nanoparticles. This work advances ion momentum spectroscopy by elucidating multi-body interaction effects and provides a robust framework for probing nanoscale internal fields, critical for applications in nanomaterial synthesis and light-matter interaction studies.