Second harmonic generation from 3D nanoantennas: on the surface and bulk contributions by far-field pattern analysis

Area of Science:

• Nonlinear Optics
• Plasmonics
• Nanophotonics

Background:

• Second harmonic generation (SHG) is a key nonlinear optical process.
• Understanding bulk vs. surface nonlinear contributions in plasmonic nanoantennas is crucial for device applications.
• Gold nanoantennas support localized surface plasmon polaritons (LSPPs) that enhance nonlinear effects.

Purpose of the Study:

• To numerically analyze SHG in dipole gold nanoantennas.
• To differentiate and study the impact of bulk and surface nonlinear terms on SHG.
• To explore how LSPPs influence the nonlinear response and the interplay between bulk and surface contributions.

Main Methods:

• Numerical simulations of SHG in gold nanoantennas.
• Analysis of far-field and near-field patterns of the second harmonic (SH) emitted field.
• Investigation of the influence of LSPP excitation on nonlinear contributions.
• Comparison of SHG under different models for nonlinear source parameters.

Main Results:

• The SH field exhibits distinct far and near-field patterns depending on whether bulk, surface, or both nonlinear contributions are considered.
• This distinction persists across different models for nonlinear source parameters.
• LSPP excitation significantly modifies the nonlinear response, enhancing surface and/or bulk contributions.
• Regimes were identified where bulk nonlinear terms dominate over surface linear terms, and vice versa.

Conclusions:

• The interplay between bulk and surface nonlinearities in gold nanoantennas is complex and strongly influenced by plasmonic resonances.
• Far-field SH patterns can serve as an experimental probe to distinguish the relative importance of bulk and surface nonlinear contributions.
• This work provides a pathway for experimentally characterizing nonlinearities in plasmonic nanostructures.