Plasmon-Plasmon Coupling Probed by Ultrafast, Strong-Field Photoemission with <7 Å Sensitivity

The coupling of propagating surface plasmon waves and localized plasmon oscillations in nanostructures is an essential phenomenon determining electromagnetic field enhancement on the nanoscale. With our recently developed experimental method [1], we can measure the maximum plasmonic field enhancement at any nanostructured metal surface. Here we use our method to investigate the fundamental question of plasmon-plasmon coupling and its effect on large field enhancement factors.