Geometry-dependent optical properties of nanostructures by FDTD simulations using experimental index parameters

Computational modelling of electromagnetic field distribution and scattering cross-section in thin-film plasmonic nanostructures is critical for the design of photonic waveguides, photosensors and wireless communications. The Finite Difference Time Domain (FDTD) method is a widely established tool for simulating such behaviours in arbitrary geometries. However, translating idealised simulations into experimental thin-film nanostructures remains challenging due to their complex multiscale nature. Exact solutions to Maxwell’s equations are further constrained by computational limits, as nanoscale discretisation demands extremely fine spatial grids. To overcome these challenges with optimised computational efficiency, we simulated a variety of thin-film nanostructures using identical refractive index parameters derived from experimental data, and compared their geometry-dependent optical responses. The modelled geometries included uniformly distributed nanoparticles, periodic hexagonal arrays, wavy surfaces and FE-SEM-imported reconstructions of experimental assemblies. The refractive index was extracted using Drude–Lorentz fitting of experimental reflectance spectra under near-normal incidence. FDTD simulations were then employed to evaluate scattering cross-sections, reflectance, transmission and electric-field distributions (both cross-sectional and normal). This correlative framework bridges theoretical and experimental insights, highlighting the influence of refractive index and geometry on light convergence, propagation and plasmon-enhanced light–matter interactions.