Near-field mapping of interference and propagation of surface plasmon polaritons in gold nanoislands

The nanoscale behavior of surface plasmon polaritons (SPPs) in gold nanostructures is directly visualized and characterized, revealing their complex interference, dispersion, and coupling dynamics. We employ a custom near-field scanning optical microscope with stable feedback control to probe these phenomena in structures fabricated via electron-beam lithography. Our experimental observations, including detailed SPP interference patterns and angle-dependent excitation, are supported by finite-difference time-domain simulations using the Tidy3D solver. The platform’s capabilities are demonstrated through a study of gold nanoislands (approximately 58nm in diameter and 25nm in height), where a 532nm excitation laser probes the near-field response. This work provides fundamental insights into plasmonic propagation modes, offering a pathway toward advanced nanophotonic devices and highly sensitive plasmonic sensors. For instance, it shows promise for plasmonic sensing applications, specifically as a probe for local dielectric changes.