Unambiguous definition of handedness for locally chiral light

Abstract

Synthetic chiral light fields were recently introduced as a novel source of chirality [Ayuso, Nat. Photonics 13, 866 (2019)10.1038/s41566-019-0531-2]. 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.