Full three-dimensional Poynting vector flow analysis of great field-intensity enhancement in specifically sized spherical-particles

Abstract

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.

Super‐Enhancement Focusing of Teflon Spheres

“…studied focusing of specifically sized dielectric spheres in their publications and they thought the unusual Poynting vector circulation and Fano resonance could result in the extraordinary near‐field focus with a large field intensity by a high‐index sphere. [ 19,20 ] In the aspect of the experiment, Peppernick et al. used to successfully observe a strong focus near the shadow surface of a polystyrene (PS) sphere (3 μm diameter) on a platinum/palladium (Pt/Pd) substrate angularly illuminated by the 400 and 800 nm lasers with a photoemission electron microscopy (PEEM).…”

Optical Phenomena in Mesoscale Dielectric Particles

“…Based on the Lorenz-Mie theory, it was found in [6] that spherical mesoscale particles with definite size parameters could cause substantially great field strength in singularities and form two extreme hotspots near the particle poles. Thus, the increase in the field intensity in the hotspots corresponded to 438 and 514 values for the size parameters of q = 22.24159 and q = 28.64159 of the Teflon sphere, respectively.…”

Optical Trapping, Sensing, and Imaging by Photonic Nanojets

“…This shows that the microsphere lenses focus the light on the sub-diffraction limited size, realizes super-resolution imaging, and traps and senses particles to enhance the spectral signal [73,74]. Using an innovative 3D mapping technique, researchers have discovered significant field intensification around the poles of dielectric microspheres by tracking field-lines passing the critical points of the Poynting vector distribution [75].…”

“…This shows that the microsphere lenses focus the light on the sub-diffraction limited size, realizes super-resolution imaging, and traps and senses particles to enhance the spectral signal [73,74]. Using an innovative 3D mapping technique, researchers have discovered significant field intensification around the poles of dielectric microspheres by tracking field-lines passing the critical points of the Poynting vector distribution [75]. In addition to spherical microlens, structures such as dielectric cubes, asymmetric cuboids, nanohole structured mesoscale dielectric spheres, and cylindrical objects can generate photonic nanojet, improve the spatial resolution of the imaging system, and even change the direction and focusing characteristics of the photonic nanojet to manipulate, sense, and image nanoscale objects [80][81][82][83][84][85][86].…”