  When circularly polarized light interacts with a nanostructure, the optical
response depends on the geometry of the structure. If the nanostructure is
chiral (i.e., it cannot be superimposed on its mirror image), then its optical
response, both in near-field and far-field, depends on the handedness of the
incident light. In contrast, achiral structures exhibit identical far-field
responses for left- and right-circular polarization. Here, we show that a
perfectly achiral nanostructure, a plasmonic metamolecule with trigonal D3h
symmetry, exhibits a near-field response that is sensitive to the handedness of
light. This effect stems from the near-field interference between the different
plasmonic modes sustained by the plasmonic metamolecule under circularly
polarized light excitation. The local chirality in a plasmonic trimer is then
experimentally evidenced with nanoscale resolution using a molecular probe. Our
experiments demonstrate that the optical near-field chirality can be imprinted
into the photosensitive polymer, turning an optical chirality into a
geometrical chirality that can be imaged using atomic force microscopy. These
results are of interest for the field of polarization-sensitive photochemistry.
