Optical chirality of vortex structured light in a temporal medium

The optical chirality of vortex structured light has attracted more and more attention in recent years due to its fascinating properties and wide potential applications. Such an issue is typically studied in a spatial medium. This work is devoted to the study of the optical chirality of vortex structured light in the temporal medium with time-varying permittivity. A full vector theoretical model is developed to describe the optical chirality of Laguerre-Gaussian (LG) vortex light beams that undergo the temporal reflection and transmission. A concept called the temporal equivalent of the photonic spin Hall effect (PSHE) is proposed to reveal the physical mechanism of controlled optical chirality of the vortex structured light in a temporal medium. It is revealed that, in the temporal medium, the distribution of the local chirality density of the LG vortex light beams is asymmetric, whereas the corresponding vortex dichroism signal is circularly symmetric. Notably, both the local chirality density and the vortex dichroism signal of the LG vortex light beams are significantly enhanced in the temporal medium. Moreover, the optical chirality of the vortex structured light can be well controlled by the anisotropic permittivity tensor of the temporal medium and the spatial incident angle. This study may provide useful insights into the interactions of vortex structured light with a temporal medium and find potential applications in the fields of chiral recognition, detection, and manipulation.