Toroidal helical pulses

Abstract Toroidal topologies and helicity are pervasive in nature and hold basic importance in scientific research. In particular, the interplay between these features gives rise to fascinating electromagnetic excitations of toroidal helices. Here, we theoretically present and experimentally realize a family of such excitations of free space, which we call toroidal helical pulses. For this purpose, we propose a configuration combining a coaxial horn emitter and an equiangular spiral grating to directly generate such single-cycle pulses. In addition to their inherent non-transverse toroidal topology and space-time nonseparability, such pulses possess controllable helicity. This work introduces a helical version of propagation toroidal electrodynamics, thereby paving the way for advanced applications, such as nontrivial light-matter interactions and data transfer.