Unambiguous definition of handedness for locally chiral light

Synthetic chiral light fields were recently introduced as a novel source of chirality [Ayuso et al., Nat. Photonics 13, 866 (2019)]. This locally chiral light spans a three-dimensional polarization that plots a chiral trajectory in space-time, leading to huge nonlinear chiral signals upon interactions with chiral media. The degree of chirality of this new form of light was defined, characterized, and shown to be proportional to the chiral signal in high harmonic generation and photo-emission. However, the sign of the light's chirality-its handedness-has not yet been defined. Standard definitions of helicity are inapplicable for locally chiral light due to its complex three-dimensional structure. Here, we define an unambiguous handedness for locally chiral fields and employ it in practical calculations.

Automated summary

Synthetic chiral light fields, introduced recently as a novel source of chirality, exhibit complex three-dimensional polarization structures and generate strong nonlinear chiral signals upon interactions. However, the sign of their chirality has not been defined, prompting researchers to propose an unambiguous definition and calculation method for their handedness.