Second-harmonic generation in plasmonic waveguides with nonlocal response and electron spill-out

TL;DR

This paper introduces a generalized method to model second-harmonic generation in plasmonic waveguides, accounting for nonlocal electron responses and spill-out effects, advancing the understanding of nonlinear optical phenomena at the nanoscale.

Contribution

It develops a comprehensive approach to include metallic nonlinearities, including quantum hydrodynamic effects, in the analysis of plasmonic waveguides.

Findings

Method enables calculation of second-harmonic generation considering nonlocal electron effects.

Quantum spill-out effects significantly influence nonlinear responses.

Applicable to design of integrated nonlinear photonic devices.

Abstract

Plasmonic waveguides provide an integrated platform to develop efficient nanoscale ultrafast photonic devices. Theoretical models that describe nonlinear optical phenomena in plasmonic waveguides, usually, only incorporate bulk nonlinearities, while nonlinearities that arise from metallic constituents remained unexplored. In this work, we present a method that enables a generalized treatment of the nonlinearities present in plasmonic waveguides and use it to calculate second-harmonic generation from free electrons through a hydrodynamic nonlocal description. As a general application of our method we also consider nonlinearities arising from the quantum hydrodynamic theory with electron spill-out. Our results may find applicability in design and analysis of integrated photonic platforms for nonlinear optics incorporating wide variety of nonlinear materials such as heavily doped semiconductors for mid-infrared applications.