Multiple scattering of light in nanoparticle assemblies: user guide for the TERMS program

TL;DR

The paper presents TERMS, an open-source Fortran program that rigorously simulates optical properties of nanoparticle clusters using the superposition T-matrix method, enabling detailed analysis of scattering, absorption, and local fields.

Contribution

It introduces the TERMS software, detailing its algorithms and capabilities for accurately modeling multiple light scattering in nanoparticle assemblies.

Findings

Accurately computes far-field cross-sections for extinction, absorption, and scattering.

Provides local field intensities and optical chirality measures.

Supports orientation-averaged optical property calculations.

Abstract

We introduce TERMS, an open-source Fortran program to simulate near-field and far-field optical properties of clusters of particles. The program solves rigorously the Maxwell equations via the superposition T-matrix method, where incident and scattered fields are decomposed into series of vector spherical waves. TERMS implements several algorithms to solve the coupled system of multiple scattering equations that describes the electromagnetic interaction between neighbouring scatterers. From this formal solution, the program can compute a number of physically-relevant optical properties, such as far-field cross-sections for extinction, absorption, scattering and their corresponding circular dichroism, as well as local field intensities and degree of optical chirality. By describing the incident and scattered fields in a basis of spherical waves the T-matrix framework lends itself to analytical formulas for orientation-averaged quantities, corresponding to systems of particles in random orientation; TERMS offers such computations for both far-field and near-field quantities of interest. This user guide introduces the program, summarises the relevant theory, and is supplemented by a comprehensive suite of stand-alone examples in the website accompanying the code.