Where Does Light Come From: Propagation and Emission of Surface Plasmon Polaritons in Plasmonic Crystals Visualized by Cathodoluminescence

Ultrafast information processing with low energy consumption is in high demand in optical networks, which leverage light in complex interconnected media, such as nanophotonic device modules. However, the nanoscopic correlation between the excitation and emission spaces of optical light─key to the foundation of nanophotonic devices, encompassing excitation (input), propagation (reservoir), and emission (output)─remains elusive. This study addresses the challenge of nanoscopic observation of optical input and output through a comprehensive investigation of the pathways in a model system based on surface plasmon polaritons in one-dimensional plasmonic crystals (PlCs), using cathodoluminescence imaging. By analyzing the momentum and emission position of optical modes, the interplay between excitation and photon emission in PlCs is clarified. The results reveal the spatial distribution of multiple emission positions across the samples arising from the modulated phases of the emitted light following point excitation of SPPs, with varying distributions and interference conditions observed for different excitation positions.