Enhanced Forward Scattering of Ellipsoidal Dielectric Nanoparticles

Zhonghua Wang,Fei Shen,Yongxuan Sun,Hongping Zhou,Zhongyi Guo,Yanhua Han,Yan Li,Ning An,Zhaoneng Jiang

doi:10.1186/s11671-016-1794-x

Abstract

Dielectric nanoparticles can demonstrate a strong forward scattering at visible and near-infrared wavelengths due to the interaction of optically induced electric and magnetic dipolar resonances. For a spherical nanoparticle, the first Kerker’s condition within dipole approximation can be realized, where backward scattering can reach zero. However, for this type of dielectric sphere, maximum forward scattering without backward scattering cannot be realized by modulating the refractive index and particle size of this nanoparticle. In this paper, we have demonstrated that a larger directional forward scattering than the traditional spherical nanoparticle can be obtained by using the ellipsoidal nanoparticle, due to the overlapping electric and magnetic dipolar modes. For the oblate ellipsoid with a determined refractive index, there is an optimum shape for generating the suppressed backward scattering along with the enhanced forward scattering at the resonant wavelength, where the electric and magnetic dipolar modes overlap with each other. For the prolate ellipsoid, there also exist the overlapping electric and magnetic dipolar modes at the resonant wavelength of total scattering, which have much higher forward scattering than those for both oblate ellipsoid and sphere, due to the existence of the higher multipolar modes. Furthermore, we have also demonstrated the realization of the dimensional tailoring in order to make the strong forward scattering shift to the desired wavelength.

Highlights

Electromagnetic waves scattered by nanoparticles has gained great attention because of its immense applications, including optical communications [1, 2], optical manipulations [3, 4], material science [5, 6], and so on
We present numerical parametric researches for the oblate ellipsoid and prolate ellipsoid by using finite element method and multipole decomposition based on electromagnetic multipole theory, which demonstrate the possibility of suppressed backward scattering and enhanced directional forward scattering
Ellipsoidal nanoparticles with different aspect ratios provide an effective method for obtaining the overlapped electric and magnetic dipole resonances

Summary

Introduction

Electromagnetic waves scattered by nanoparticles has gained great attention because of its immense applications, including optical communications [1, 2], optical manipulations [3, 4], material science [5, 6], and so on. The interactions between the electric and magnetic modes allow to fulfill certain conditions, which can generate directional scattering [7–14]. Such certain condition was called Kerker’s condition which was first proposed with small magnetodielectric spheres in 1983 [7], including the first Kerker’s condition for zero backward scattering (BS) and the second Kerker’s condition for minimum forward scattering (FS). In the middle of these two particular scattering properties, suppressed backward scattering and enhanced directional forward scattering are typically of more practical application, such as in optical antennas [15–17], plasmon-enhanced photovoltaics [18, 19], and other devices based on optically induced “negative forces” [20]

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