Optical superchirality and electromagnetic angular momentum

The recent interest in "superchiral" fields, generated near planar chiral metamaterials, has prompted questions of deeper links between beam helicity and optical angular momentum. To address the issues invites consideration of the most appropriate metrics and their physical interpretation. This paper develops the photonic attributes of the chirality density, one of several measures that are conserved quantities for a vacuum electromagnetic field. The chirality density is explored with reference to an arbitrary polarization basis, and related to optical angular momentum. Analyzing multi-mode beams with complex wavefront structures affords a deeper understanding of the interplay between optical chirality and angular momentum.