Controlling steady-state second harmonic signal via linear and nonlinear Fano resonances

TL;DR

This paper compares how linear and nonlinear Fano resonances in plasmonic nanoparticles can control and enhance steady-state second harmonic signals, revealing different mechanisms for signal amplification.

Contribution

It introduces a steady-state analysis of second harmonic enhancement via linear and nonlinear Fano resonances, highlighting their distinct roles in nonlinear signal control.

Findings

Linear Fano resonance enhances hot spot fields, boosting nonlinear signals.

Nonlinear Fano resonance enhances signals without hot spot field increase.

Steady-state analysis distinguishes between the two resonance effects.

Abstract

Nonlinear signal even from a single molecule becomes visible at hot spots of plasmonic nanoparticles. In these structures, Fano resonances can control the nonlinear response in two ways. \textit{(i)} A linear Fano resonance can enhance the hot spot field, resulting enhanced nonlinear signal. \textit{(ii)} A nonlinear Fano resonance can enhance the nonlinear signal without enhancing the hot spot. In this study, we compare the enhancement of second harmonic signal at the steady-state obtained via these two methods. Since we are interested in the steady-state signal, we adapt a linear enhancement which works at the steady-state. This is different than the dark-hot resonances that appears in the transparency window due to enhanced plasmon lifetime.