Nonlinearity-induced optical torque

TL;DR

This paper introduces a novel mechanism for transferring angular momentum to non-absorbing particles through nonlinear light scattering, enabling optical torque without absorption or symmetry breaking.

Contribution

It proposes a new physical mechanism for optical torque via nonlinear scattering, expanding understanding of light-matter interactions in non-absorbing particles.

Findings

Nonlinear negative optical torque observed at harmonic resonances

Symmetry breaking occurs at the microscopic level in nonlinear scattering

Potential for experimental verification with dielectric nanostructures

Abstract

Optically-induced mechanical torque leading to the rotation of small objects requires the presence of absorption or breaking cylindrical symmetry of a scatterer. A spherical non-absorbing particle cannot rotate due to the conservation of the angular momentum of light upon scattering. Here, we suggest a novel physical mechanism for the angular momentum transfer to non-absorbing particles via nonlinear light scattering. The breaking of symmetry occurs at the microscopic level manifested in nonlinear negative optical torque due to the excitation of resonant states at the harmonic frequency with higher projection of angular momentum. The proposed physical mechanism can be verified with resonant dielectric nanostructures, and we suggest some specific realizations.