Evolving electromagnetic chirality of a focused field from the Poincaré sphere perspective

Abstract

Chirality, which describes not only the three-dimensional mirror-symmetry violation of objects but also the local handedness and spatial geometrical structure of electromagnetic fields, has gained enormous interest recently because of its fundamental features as well as practical and potential applications in chiral light–matter interactions. Analytical forms of the electric and magnetic field strength vectors as well as optical chirality density and flow of strongly focused full Poincaré sphere beams are presented. The evolution of nonparaxial electromagnetic chirality of input fields from the Poincaré sphere view is explored; in addition its roles in relation to ellipticity, handedness, and orientation are revealed based on the analytical model. Ellipticity affects the localization and magnitude of both chirality density and flow. In contrast, handedness mainly affects the magnitude of the optical chirality density and longitudinal component of flow, whereas both density and flow are independent of the input orientation. Moreover, the structure and appearance of the optical chirality density are dominated by the longitudinal component of its flow. These findings may be of help in chiral particle trapping, nanoscale chiral detection, and sensing.