Intrinsic nonlinear response of surface plasmon polaritons

TL;DR

This paper presents a model linking the intrinsic nonlinear response of surface plasmon polaritons to the third-order nonlinear susceptibility of metals, accounting for high losses and enabling better understanding of nonlinear plasmonic devices.

Contribution

It introduces a novel model that relates SPP nonlinear response to metal susceptibility, considering high loss effects, and reveals sign differences in nonlinear coefficients.

Findings

Sign difference between nonlinear propagation coefficient and susceptibility.

Model accounts for high metal losses in nonlinear SPP propagation.

Enables extraction of complex nonlinear susceptibility of gold.

Abstract

We offer a model to describe the intrinsic nonlinear response of surface plasmon polaritons (SPPs). Relation of the complex nonlinear coefficient of SPPs to the third-order nonlinear susceptibility of the metal is provided. As reported in a recent study, gold is highly lossy and simultaneously highly nonlinear due to interband absorption and interband thermo-modulation at a wavelength shorter than 700 nm. The effect of the high loss of the metal on the SPP nonlinear propagation is taken into account in our model. With the model we show difference in sign of real and imaginary parts between the nonlinear propagation coefficient and the nonlinear susceptibility of component material for the first time to our knowledge. Our model could have practical importance in studying plasmonic devices utilizing the nonlinear phase modulation and the nonlinear absorption of SPPs. For example, it allows one to extract the complex nonlinear susceptibility of gold through a measurement of SPP nonlinear propagation at the visible range.