Ab initio derivation of multipolar expansion of optical force

TL;DR

This paper derives the multipolar expansion of optical force from first principles, modeling particles as collections of point charges or dipoles, providing clearer physical and mathematical insights.

Contribution

It offers an ab initio derivation of optical force multipolar expansion, clarifying the role of fundamental charges unlike previous assumptions of radiation multipoles.

Findings

Derivation aligns with previous multipolar expressions

Provides transparent physical interpretation

Enhances understanding of charge contributions in optical forces

Abstract

Like many other physical quantities, the optical force can be expanded using multipole expansion, which has been done in [Nat. Photon. 5, 531], up to electric octupole order. However, in that study, the existence of radiation multipoles were pre-assumed, and the role of the fundamental building units, charges, are not evident. Here, we derive the same multipolar expression of optical force by treating the particles as a collection of point charges or point dipoles, which results in more transparent physics and mathematics.