The optical torque on small bi-isotropic particles

TL;DR

This paper derives comprehensive equations for the optical torque on small bi-isotropic particles, revealing additional interference effects that impact energy and angular momentum conservation, with implications for phenomena like negative torque.

Contribution

It introduces a complete theoretical framework for optical torque on bi-isotropic particles, including interference terms previously neglected.

Findings

Interference of scattered fields affects optical torque calculations.

Additional terms influence conservation laws and negative torque phenomena.

Theoretical equations align with experimental observations.

Abstract

Most previous theoretical studies on the optical torque exerted by light on dipolar particles are incomplete. Here we establish the equations for the time-averaged optical torque on dipolar bi-isotropic particles. Due to the interference of scattered fields, it has a term additional to that commonly employed in theory and experiments. Its consequences for conservation of energy, angular momentum, and effects like negative torques, are discussed.