Effective nonlinear optical properties of composite media of graded spherical particles

TL;DR

This paper introduces a nonlinear differential effective dipole approximation (NDEDA) to analyze the linear and third-order nonlinear susceptibilities of composite media with graded spherical particles, revealing enhanced optical properties and broad resonant effects.

Contribution

The paper develops a new NDEDA method and derives exact local fields for graded particles, providing a comprehensive approach to study nonlinear optical properties in composite media.

Findings

Gradation in metal particles broadens surface plasmon resonance

Enhanced optical nonlinearity and figure of merit in graded composites

Excellent agreement between NDEDA and first-principles calculations

Abstract

We have developed a nonlinear differential effective dipole approximation (NDEDA), in an attempt to investigate the effective linear and third-order nonlinear susceptibility of composite media in which graded spherical inclusions with weak nonlinearity are randomly embedded in a linear host medium. Alternatively, based on a first-principles approach, we derived exactly the linear local field inside the graded particles having power-law dielectric gradation profiles. As a result, we obtain also the effective linear dielectric constant and third-order nonlinear susceptibility. Excellent agreement between the two methods is numerically demonstrated. As an application, we apply the NDEDA to investigate the surface plasma resonant effect on the optical absorption, optical nonlinearity enhancement, and figure of merit of metal-dielectric composites. It is found that the presence of gradation in metal particles yields a broad resonant band in the optical region, and further enhances the figure of merit.