Multipolar expansions for scattering and optical force calculations beyond the long wavelength approximation

TL;DR

This paper reviews three methods for calculating electromagnetic multipoles and demonstrates their application in accurately modeling scattering and optical forces on particles across a broad wavelength spectrum.

Contribution

It identifies the spherical multipoles as the most suitable for scattering calculations and applies them to analyze optical forces on various particles beyond the long wavelength approximation.

Findings

Spherical multipoles are most effective for scattering analysis.

Optical forces can be accurately computed across a wide wavelength range.

The methods extend the applicability beyond the long wavelength approximation.

Abstract

We review three different approaches for the calculation of electromagnetic multipoles, namely the Cartesian primitive multipoles, the Cartesian irreducible multipoles and the spherical multipoles. We identify the latter as the best suited to describe the scattering of electromagnetic radiation, as exemplified for an amorphous silicon sphere. These multipoles are then used to calculate the optical force acting on semiconductor, dielectric or metallic particles in a wide wavelength range, from the dipolar down to the Mie regimes.