Wave-mixing origin and optimization in single and compact aluminum nanoantennas

TL;DR

This paper investigates second-harmonic generation in single aluminum nanoantennas, demonstrating enhanced resonant effects and separating different nonlinear contributions, with implications for nanoscale nonlinear optics.

Contribution

It reveals the physical origin of SHG in aluminum nanoantennas as mainly from local surface sources and achieves doubly resonant regimes in compact structures.

Findings

7.5 times enhancement in doubly resonant regime

Separation of surface and bulk nonlinear contributions

Quantitative agreement between experiments and simulations

Abstract

The outstanding optical properties for plasmon resonances in noble metal nanoparticles enable the observation of non-linear optical processes such as second-harmonic generation (SHG) at the nanoscale. Here, we investigate the SHG process in single rectangular aluminum nanoantennas and demonstrate that i) a doubly resonant regime can be achieved in very compact nanostructures, yielding a 7.5 enhancement compared to singly resonant structures and ii) the \(\chi_{\perp\perp\perp}\) local surface and \(\gamma_{bulk}\) nonlocal bulk contributions can be separated while imaging resonant nanostructures excited by a tightly focused beam, provided the \(\chi_{\perp\parallel\parallel}\) local surface is assumed to be zero, as it is the case in all existing models for metals. Thanks to the quantitative agreement between experimental and simulated far-field SHG maps, taking into account the real experimental configuration (focusing and substrate), we identify the physical origin of the SHG in aluminum nanoantennas as arising mainly from \(\chi_{\perp\perp\perp}\) local surface sources.