Optical helicity of unpolarized light

TL;DR

This paper demonstrates that 3D structured optical vortices can exhibit optical helicity independent of polarization, implying unpolarized light can show optical activity and chiral interactions, unlike classical optics.

Contribution

It reveals that optical helicity in structured vortices is polarization-independent, expanding understanding of light-matter interactions beyond classical polarization dependence.

Findings

Optical helicity density contribution is polarization-independent in 3D optical vortices.

Unpolarized light can exhibit optical activity and chiral interactions.

Contrasts with classical optics where polarization determines optical properties.

Abstract

Recently arXiv:2004.02970 showed that the extraordinary transverse spin momentum density of spatially confined optical fields is largely independent of polarization. Here it is shown that 3D structured optical vortices which possess the phase factor $exp(il\phi)$ have a contribution to the optical helicity density which is completely independent of polarization. In stark contrast to what is known in classical optics with plane waves and paraxial light, the physical consequence is that unpolarized light can exhibit optical activity and chiral light-matter interactions.