treams -- A T-matrix scattering code for nanophotonic computations

TL;DR

treams is a versatile, efficient software package for electromagnetic scattering calculations using the T-matrix method, supporting periodic boundaries, multiple basis sets, and complex media, facilitating advanced nanophotonic research.

Contribution

The paper introduces treams, a new comprehensive T-matrix scattering code with support for periodic boundaries, multiple basis sets, and chiral media, enhancing computational capabilities in nanophotonics.

Findings

Demonstrated field calculations in various lattice structures

Explored quasi-bound states in the continuum

Validated the code with physical system simulations

Abstract

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. 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 moir\'{e} 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. The full code is published at https://github.com/tfp-photonics/treams with the documentation at https://tfp-photonics.github.io/treams .