Tuning of plasmonic surface lattice resonances: on the crucial impact of the excitation efficiency of grazing diffraction orders.

Metallic nanoparticles exhibit remarkable optical properties through localized surface plasmon (LSP) resonances. When arranged in arrays, nanoparticles form surface lattice resonances (SLRs) affected by inter-particle distance. SLRs can offer narrower bandwidths and stronger electric field enhancements than LSP modes, crucial for efficient optical device development. Among important aspects, grazing diffracted orders crucially impact SLR properties, facilitating long-range nanoparticle interactions. This study explores how these photonic modes propagating at the substrate surface influence SLRs, by using experimental and theoretical approaches, including Finite Difference Time Domain simulations on gold disk arrays. Results show SLR properties strongly rely on diffracted mode efficiency controlled by the grating constant along the incident polarization. Notably, large inter-particle spacing along the incident polarization can strongly reduce the SLR red-shift. Understanding and managing long-range interactions in engineered plasmonic structures are highlighted, providing insights for enhanced performance in advanced photonic and optoelectronic devices.