Two-dimensional spiral
plasmonic structures have emerged as a versatile
approach to generate near-field vortex fields with tunable topological
charges. We demonstrate here a far-field approach to observe the chiral
second-harmonic generation (SHG) at designated visible wavelengths
from a single plasmonic vortex metalens. This metalens comprises an
Archimedean spiral slit fabricated on atomically flat aluminum epitaxial
film, which allows for precise tuning of plasmonic resonances and
subsequent transfer of two-dimensional materials on top of the spiral
slit. The nonlinear optical measurements show a giant SHG circular
dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion
efficiency (about an order of magnitude greater than the bare aluminum
lens) from monolayer tungsten disulfide (WS2)/aluminum
metalens, which is designed at the C-exciton resonance of WS2. Since the C-exciton is not a valley exciton, the enhanced chiral
SHG in this hybrid system originates from the plasmonic vortex field-enhanced
SHG under the optical spin–orbit interaction.