Temporal Optical Activity and Chiral Time-Interfaces [Invited].

Time-interfaces, at which the optical properties of a medium undergo abrupt and spatially uniform changes, have attracted surging interest in optics and wave physics. In this work, we study wave scattering at time-interfaces involving chiral media. Dual to spatial interfaces involving chiral media, we show that a propagating wave is split upon a chiral time-interface into two orthogonal circular polarization waves oscillating at different frequencies. We formulate the temporal scattering boundary-value problem at such time-interfaces, and then demonstrate the effect of temporal optical activity through a chiral time-slab. The effect of material dispersion is also analyzed, highlighting interesting opportunities in which multiple scattered waves emerge form the time-interface and interfere. Our results pave the way towards time-metamaterials encompassing chirality as an additional degree of freedom for wave manipulation, offering opportunities for temporal circular dichroism and negative refraction at time-interfaces.