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arXiv · 2603.14071

Beyond optical chirality density: tensor-based description of electromagnetic chirality

Ilia Smagin·Sergey Dyakov
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Abstract

Optical chirality density is widely used as a local scalar measure of the chirality of an electromagnetic field and its interaction with isotropic chiral matter. However, within the dipole approximation, a general bi-anisotropic material response probes direction-dependent field bilinears that cannot, in general, be reduced to a single pseudoscalar. This necessitates the development of a systematic tensorial formulation to describe the coupling between arbitrary fields and general reciprocal bi-anisotropic media. To this end, we extend the Tang--Cohen formalism to a general anisotropic optical-activity pseudotensor, treating its trace and traceless symmetric and antisymmetric parts separately. We demonstrate while the trace part couples to classical optical chirality density, the traceless symmetric part is probed by the five Lipkin densities $Z^{ab0}$, which form part of the Lipkin tensor. On the other hand, for the antisymmetric part of the optical-activity pseudotensor, the coupling term is proportional to the reactive part of the local Poynting vector. Finally, we provide numerical examples of pseudo-chiral and anisotropic chiral electromagnetic fields and study their interaction with different bi-anisotropic media. The developed framework offers a systematic tensorial description of chiral and pseudo-chiral light-matter coupling. Importantly, our analysis identifies which specific field quantities must be enhanced to optimize the magneto-electric coupling in such media.

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Ilia Smagin, Sergey Dyakov. 2026-08-11. Beyond optical chirality density: tensor-based description of electromagnetic chirality. https://arxiv.org/abs/2603.14071

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