Observation of a Giant Nonlinear Chiro‐Optical Response in Planar Plasmonic–Photonic Metasurfaces

Plasmonic nanosystems and metamaterials have recently attracted considerable attention because of their ability to enhance the light–matter interactions. One of such optical phenomena is the chiral‐ or handedness‐dependent response which typically requires 3D samples. Planar structures that can exhibit chiral response are highly desirable because of their facile fabrication, however fundamental challenges arising from the 2D nature of these systems prevent the generation of strong chiro‐optical effects. In this work, giant enhancement of the handedness‐dependent optical response in planar metallic nanostructures is shown by exploring the hybridization of plasmonic–photonic modes in a chiral metasurface. The resulting planar hybrid metasurface exhibits over an order of magnitude difference in nonlinear optical response when illuminated with excitation light of opposite circular polarizations. The unique properties of the hybridized plasmonic–photonic modes are shown to be responsible for the giant chiral nonlinear response. This platform allows to study the fundamental framework of chiral optical effects that arise from the combination of planar chirality and collective interaction of discrete nanosystems.