Yue Liyang, Yan Bing, Monks James N, Dhama Rakesh, Jiang Chunlei, Minin Oleg V, Minin Igor V, Wang Zengbo
School of Computer Science and Electronic Engineering, Bangor University, Dean Street, Bangor, Gwynedd, LL57 1UT, UK.
College of Electrical and Information Engineering, Northeast Petroleum University, Daqing, 163318, China.
Sci Rep. 2019 Dec 27;9(1):20224. doi: 10.1038/s41598-019-56761-9.
The Poynting vector plays a key role in electrodynamics as it is directly related to the power and the momentum carried by an electromagnetic wave. Based on the Lorenz-Mie theory, we report on the focusing effect of a spherical particle-lens by properly analysing the Poynting vector maps. Conventional two-dimensional (2D) maps showing Poynting vector magnitude and direction in a given plane cannot deliver information on three-dimensional (3D) directivity and vectorisation in key regions of singularities, such as vortexes and saddle points, due to poor expressiveness. In this article, an analytical 3D mapping technology is utilised to track the field-features passing through the singularities of the distribution of the Poynting vector in a spherically dielectric mesoscale particle-lens. We discovered that the spheres with the certain size parameters can stimulate extremely large field-intensity at singularities and then form two circular hotspots around the sphere poles. An astonishing large 'heart-shape' 3D Poynting vector circulation, which cannot be predicted by conventional 2D mapping analysis, is found to provide a great angular variation within an enormous range in these spheres. We anticipate that this effect will contribute to the field-enhancement phenomena, such as surface enhances Raman scattering, surface enhances absorption, super-resolution imaging and others.
坡印廷矢量在电动力学中起着关键作用，因为它与电磁波携带的功率和动量直接相关。基于洛伦兹 - 米氏理论，我们通过对坡印廷矢量图进行适当分析，报告了球形粒子透镜的聚焦效应。传统的二维（2D）图展示了给定平面内坡印廷矢量的大小和方向，但由于表现力欠佳，无法在奇点的关键区域（如涡旋和鞍点）提供关于三维（3D）方向性和矢量化的信息。在本文中，我们利用一种解析三维映射技术来追踪穿过球形介电中尺度粒子透镜中坡印廷矢量分布奇点的场特征。我们发现，具有特定尺寸参数的球体能够在奇点处激发极大的场强，进而在球体两极周围形成两个圆形热点。我们发现了一种惊人的大 “心形” 三维坡印廷矢量环流，这是传统二维映射分析无法预测的，它在这些球体中能在极大范围内提供巨大的角度变化。我们预计这种效应将有助于实现场增强现象，如表面增强拉曼散射、表面增强吸收、超分辨率成像等。
