Spatially confined vector fields at material-induced resonances in near-field-coupled systems

Area of Science:

• Nanophotonics and Plasmonics
• Surface Science and Spectroscopy
• Materials Characterization

Background:

• Local electric fields are crucial for near-field optical microscopy, especially for heterogeneous or anisotropic nanomaterials.
• Scattering-type near-field optical microscopy (s-SNOM) is a primary technique for quantifying nanoscale electric fields.
• Traditional s-SNOM primarily analyzes the perpendicular (z) electric field component under specific illumination conditions.

Purpose of the Study:

• To explore the local electric vector-field behavior in a particle-tip/substrate system using s-SNOM.
• To compare finite element modeling simulations with the analytical tip-dipole model for different excitation scenarios.
• To investigate the potential of resonant excitation for probing in-plane electric field components.

Main Methods:

• Parametric simulations using finite element modeling (FEM) at mid-infrared wavelengths.
• Comparison of FEM results with the standard analytical tip-dipole model.
• Analysis of four excitation combinations: resonant/non-resonant tip and sample excitation.

Main Results:

• All simulated scenarios exhibit 3D field confinement under the particle tip.
• Resonant sample excitation leads to extremely strong field enhancements and vector fields along all Cartesian coordinates, even without breaking symmetry.
• In-plane resonant sample excitation shows field enhancements exceeding 6 orders of magnitude compared to standard p-polarized non-resonant excitation.
• Diverse spatial field distributions are observed, including fields perpendicular to the surface and spatially rotating fields within and at the sample surface.

Conclusions:

• Resonant excitation in s-SNOM enables access to the full local electric vector field.
• This technique allows for the quantification of tensorial properties in nanoscale materials.
• Modern s-SNOM is capable of probing complex, multi-directional electric fields at the nanoscale.