Chiral Light-Matter Interaction for Controlling Nanoplasmonic Fields.

The dichroic response of plasmonic nanostructures shows great potential for controlling chiral light-matter interactions. This approach is also promising for all-optical switching using low-intensity optical beams. In this work, plasmonic circular dichroism is demonstrated using closely spaced gold nanoparticle dimers, exhibiting high near-field contrast under left-circularly polarized (LCP) and right-circularly polarized (RCP) illumination. Using scanning near-field optical microscopy (SNOM), the dichroic behavior of the dimers under LCP and RCP illumination is mapped, enabling hot spots to become cold spots with full optical control. More importantly, the eigenmode excitations and their contributions to the plasmonic chiroptical response are directly revealed, which enables the complete understanding of the chiral behavior in complex nanostructures. These findings are valuable for designing nanophotonic devices.