论文标题
小颗粒在光散射中的极化奇异性
Polarization Singularities in Light Scattering by Small Particles
论文作者
论文摘要
使用全波数值模拟和分析多极扩展，我们研究了下空间极化奇异性的特性，这些奇点在亚波长颗粒中出现在光散射中。我们考虑了由介电或完美电导材料制成的球形和圆环颗粒。我们确定了近场和远场区域的拓扑指数和电场极化奇异性的轨迹。在远场区域中，总共确定了四个奇点，其极化拓扑指数的总和是两个，与粒子的几何形状无关。在近场区域，极化奇异性在很大程度上取决于粒子的形状和入射光的极化，并且由于磁场的非透明性质，它们的索引总和不再由庞加尔 - 霍普定理控制。从近场到远场，C线的极化拓扑指数可能会发生变化。奇异点的远场特性可以通过激发多物的干扰很好地解释，但是它们的近场特性可以受到未被多层扩展未捕获的evaneSentIct场的强烈影响。我们的工作发现了粒子的几何特性与散射场的极化奇异性之间的重要关系。结果可以应用于操纵纳米光系统中的极化奇异性，并可以在光学传感中产生新的应用。
Using full-wave numerical simulations and analytical multipole expansions we investigated the properties of real-space polarization singularities that emerge in light scattering by subwavelength particles. We considered spherical and torus particles made of dielectric or perfect-electric-conductor material. We determined the topological indices and the trajectories of electric-field polarization singularities in both the near-field and far-field regions. In the far-field region, a total of four singularities are identified and the sum of their polarization topological indices is two, independent of the particle's geometric shape. In the near-field region, the polarization singularities strongly depend on the particle's shape and the polarization of incident light, and their index sum is not governed by the Poincaré-Hopf theorem anymore due to the non-transverse nature of the fields. From near field to far field, a flipping of sign can happen to the polarization topological indices of the C lines. The far-field properties of the singularities can be well explained by the interference of the excited multipoles, but their near-field properties can be strongly affected by the evanescent fields that are not captured by the multipole expansions. Our work uncovers the important relationship between particles' geometric properties and the polarization singularities of their scattering field. The results can be applied to manipulate polarization singularities in nanophotonic systems and could generate novel applications in optical sensing.
