Grating-Coupled Plasmonic Resonances in Symmetric 2D Gold Nanobump Grating: Theory Meets Experiments

The excitation of hybridized plasmonic modes is induced by periodic, two-dimensional gratings. Hybrid lattice plasmon resonances (HLPRs) emerge from the interaction of surface plasmon polaritons (SPPs), localized surface plasmons (LSPs), and grating-induced light diffraction and scattering. These resonances are characterized by dispersive and narrow line widths, which are particularly relevant for biosensing and surface-enhanced spectroscopies. In this comprehensive investigation, the diffraction-based excitation of HLPR resonances in a symmetric 2D gold nanobump grating is examined with excitation occurring across multiple lattice planes. The resonance tunability with respect to azimuthal and incidence angles, as well as polarization, is experimentally investigated. To identify and validate the origins of the resonant peaks, theoretical calculations of the spectral and near-field responses were conducted, providing a thorough examination of the phenomena. This combined theoretical-experimental study highlights the pivotal role of symmetry and excitation geometry in defining hybrid plasmonic modes, thereby providing guidelines for the engineering of highly tunable plasmonic platforms.