Observation of helical pulses.

Abstract

Ultrafast spatiotemporal vortex pulses constitute a category within spatiotemporal topological waves. Nevertheless, the experimental realization of helical pulses-single- or few-cycle short vortex pulses characterized by space-time nonseparability-remains elusive to date. Here, we introduce two complementary methods for experimentally generating such space-time nonseparable helical pulses (SNHPs) in the optical and microwave spectral regimes. We achieve few-cycle quasi-linearly polarized SNHPs by decomposing the optical toroidal pulses into their polarization components. We also generated single-cycle non-transverse SNHPs directly from a microwave ultrawideband spiral emitter. These approaches enable the experimental realization of SNHPs and provide a platform for further investigation into their properties and applications, such as nontrivial light-matter interactions and optical communications.