treams – a T-matrix-based scattering code for nanophotonics

We report the publication of treams, a new software for electromagnetic scattering computations based on the T-matrix method. Besides conventional T-matrix calculations for individual scatterers and finite clusters of particles, a unique feature of the code is its full support for periodic boundaries in one, two, and all three spatial dimensions. We use highly efficient and quickly converging lattice summation techniques based on the Ewald method to evaluate the arising lattice sums in these cases. In addition to the common use of vector spherical waves as a basis set for the T-matrix, vector cylindrical waves are also implemented. To describe stratified media, vector plane waves are used with an S-matrix description of the electromagnetic scattering. All basis sets and the associated methods can be used together with chiral constitutive relations. Thereby, chiral embedding media are supported, as well as scatterers made from chiral materials.

This contribution outlines the basic methods implemented and the program structure. Two interfaces to the implemented functionality are available: a flexible and fast low-level interface and a high-level interface for added convenience and plausibility checks. We conclude with two examples: a demonstration of the field calculation in various lattices and the explorations of quasi-bound states in the continuum. The presented code was already used in calculations for various physical systems: from the mode properties of molecular arrays in cavities to analytical models for metasurfaces and from moiré lattices to the homogenization of artificial photonic materials. With the publication of treams and the associated documentation, we hope to empower more scientists to make an efficient, fast, and precise exploration of nanophotonic systems that can be described in the broader framework of scattering theory.

本报告公布了一种名为 treams 的新型软件，该软件基于 T 矩阵法进行电磁散射计算。除了对单个散射体和有限粒子群的传统 T 矩阵计算外，该代码的独特之处在于其对一维、二维以及三维空间中周期边界的全面支持。我们采用了基于 Ewald 方法的效率极高且收敛迅速的晶格求和技巧，以评估这些情况中产生的晶格和。除了将矢量球面波作为 T 矩阵的基函数的常规用法外，矢量柱面波也得到了实现。为了描述分层介质，我们采用了矢量平面波，并结合 S 矩阵描述的电磁散射。所有基函数及其相关方法均可与手征本构关系结合使用，从而支持手征嵌入介质，以及由手征材料制成的散射体。本文概述了所实现的基本方法和程序结构。实现了两种对实施功能的外部接口：一种灵活快速的低级接口，以及一种为便利性和合理性检查提供的高级接口。我们以两个示例作为结论：在不同晶格中的场计算演示，以及连续体中准束缚态的探索。所提出的代码已用于各种物理系统的计算：从腔中分子阵列的模式特性到超表面分析模型的建立，从摩尔纹晶格到人工光子材料均质化的研究。随着 treams 及其相关文档的发布，我们期望能够助力更多科学家高效、快速、精确地探索可描述于散射理论更广泛框架下的纳米光子系统。