Rotating chiral dipoles for unidirectional scattering

Vectorial optical fields have recently attracted significant attention due to their importance in sensing, imaging, light-matter interactions and controlling photonic responses of nanoparticles and nanostructures. In this respect, the interaction of polarised fields with chiral nano-objects is of particular interest because controlling directionality of scattering via chirality of light or nanostructures would open up new applications in nanophotonics and photochemistry. Here, a novel concept of rotating chiral dipoles is introduced to obtain the relationship between the directionality and the handedness of scattering fields and realize unidirectional chiral scattering. Through the engineering of multipole excitation in plasmonic helicoid nanoparticles, we systematically introduce and demonstrate, both numerically and experimentally, the rotating chiral dipole for highly-directional forward scattering of circularly-polarized light. This concept of rotating chiral dipoles may be important for designing scattering from nanostructures and optical nano-antennas.