Fano enhancement of SERS signal without increasing the hot spot intensity

TL;DR

This paper introduces a method to significantly enhance SERS signals via Fano resonance-induced path interference, achieving higher signals without increasing hot spot intensity or damaging molecules.

Contribution

The study presents an analytical and numerical approach to enhance SERS signals through nonlinear Fano interference, avoiding hot spot damage and mode modification.

Findings

SERS enhancement factor of 10^2 to 10^3 achieved.

Enhancement occurs without increasing hot spot intensity.

Path interference in nonlinear response is demonstrated.

Abstract

Plasmonic nanostructures enhance nonlinear response, such as surface enhanced Raman scattering (SERS), by localizing the incident field into hot spots. The localized hot spot field can be enhanced even further when linear Fano resonances (FR) take place in a double resonance scheme. However, hot spot enhancement is limited with the modification of the vibrational modes, the break-down of the molecule and the tunnelling regime. Here, we present a method which can circumvent these limitations. Our analytical model and solutions of 3D Maxwell equations show that: enhancement due to the localized field can be multiplied by a factor of $10^2$ to $10^3$. Moreover, this can be performed without increasing the hot spot intensity which also avoids the modification of the Raman modes. Unlike linear Fano resonances, we create a path interference in the nonlinear response. We demonstrate on a single equation that enhancement takes place due to cancellation of the contributing terms in the denominator of the SERS response.