  The ability to manipulate the electric-field vector of broadband terahertz
waves is essential for applications of terahertz technologies in many areas,
and can open up new possibilities for nonlinear terahertz spectroscopy and
coherent control. Here, we propose a novel laser-driven terahertz emitter,
consisting of metasurface-patterned magnetic multilayer heterostructures. Such
hybrid terahertz emitters can combine the advantages of spintronic emitters for
being ultrabroadband, efficient and flexible, as well as those of metasurfaces
for the unique capability to manipulate terahertz waves with high precision and
degree of freedom. Taking a stripe-patterned metasurface as an example, we
demonstrate the generation of broadband terahertz waves with tunable chirality.
Based on experimental and theoretical studies, the interplay between the
laser-induced spintronic-origin currents and the metasurface-induced transient
charges/currents are investigated, revealing the strong influence on the device
functionality originated from both the light-matter interactions in individual
metasurface units and the dynamic coupling between them. Our work not only
offers a flexible, reliable and cost-effective solution for chiral terahertz
wave generation and manipulation, but also opens a new pathway to
metasurface-tailored spintronic devices for efficient vector-control of
electromagnetic waves in the terahertz regime.
