Numerical Analysis of Localized Electric Field Enhancement in Apertureless Near Field Optical Microscopy

In this work, we investigate the effects of two distinct physical mechanisms, the antenna effect and plasmon resonance, on electric field enhancement in representative geometrical structures and at the apex of a sharp tip. The three-dimensional (3D) apertureless surface near-field optical microscopy (a-SNOM) configuration is numerically investigated using a finite element method (FEM). Our results show good agreement with analytical predictions and prior numerical benchmarks. Accounting for both antenna effects and plasmon resonances is crucial for accurate modeling of local field amplification in nanostructured probes. Through a systematic parametric numerical study, we show that field enhancement is strongly influenced by illumination conditions, polarization angle, and tip geometry. Finally, these results clarify how intrinsic material properties, extrinsic geometric features, and optical excitation govern field enhancement in nanostructures.