Ramirez-Cuevas Francisco V, Gurunatha Kargal L, Parkin Ivan P, Papakonstantinou Ioannnis
Photonic Innovations Lab, Department of Electronic and Electrical Engineering, University College London, London, WC1E 7JE, United Kingdom.
Center for Energy Transition, Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Santiago, 7941169, Chile.
ACS Photonics. 2022 Feb 16;9(2):672-681. doi: 10.1021/acsphotonics.1c01710. Epub 2022 Feb 4.
Disordered nanostructures are commonly encountered in many nanophotonic systems, from colloid dispersions for sensing to heterostructured photocatalysts. Randomness, however, imposes severe challenges for nanophotonics modeling, often constrained by the irregular geometry of the scatterers involved or the stochastic nature of the problem itself. In this Article, we resolve this conundrum by presenting a universal theory of averaged light scattering of randomly oriented objects. Specifically, we derive expansion-basis-independent formulas of the orientation-and-polarization-averaged absorption cross section, scattering cross section, and asymmetry parameter, for single or a collection of objects of arbitrary shape. These three parameters can be directly integrated into traditional unpolarized radiative energy transfer modeling, enabling a practical tool to predict multiple scattering and light transport in disordered nanostructured materials. Notably, the formulas of average light scattering can be derived under the principles of fluctuational electrodynamics, allowing the analogous mathematical treatment to the methods used in thermal radiation, nonequilibrium electromagnetic forces, and other associated phenomena. The proposed modeling framework is validated against optical measurements of polymer composite films with metal-oxide microcrystals. Our work may contribute to a better understanding of light-matter interactions in disordered systems, such as plasmonics for sensing and photothermal therapy, photocatalysts for water splitting and CO dissociation, photonic glasses for artificial structural colors, and diffuse reflectors for radiative cooling, to name just a few.
无序纳米结构在许多纳米光子系统中普遍存在，从用于传感的胶体分散体到异质结构光催化剂。然而，随机性给纳米光子学建模带来了严峻挑战，通常受到所涉及散射体不规则几何形状或问题本身随机性的限制。在本文中，我们通过提出一种随机取向物体平均光散射的通用理论来解决这一难题。具体而言，我们推导了单个或任意形状物体集合的取向和偏振平均吸收截面、散射截面以及不对称参数的与展开基无关的公式。这三个参数可以直接整合到传统的非偏振辐射能量传输建模中，从而形成一个预测无序纳米结构材料中多次散射和光传输的实用工具。值得注意的是，平均光散射公式可以在波动电动力学原理下推导得出，这使得其能够采用与热辐射、非平衡电磁力及其他相关现象中所用方法类似的数学处理方式。所提出的建模框架通过对含有金属氧化物微晶的聚合物复合薄膜的光学测量进行了验证。我们的工作可能有助于更好地理解无序系统中的光与物质相互作用，例如用于传感和光热疗法的等离子体学、用于水分解和一氧化碳解离的光催化剂、用于人造结构色的光子玻璃以及用于辐射冷却的漫反射器等等。
