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Local Optical Chirality Induced by Near-Field Mode Interference in Achiral Plasmonic Metamolecules
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posted on 2019-12-13, 20:08 authored by Andreas Horrer, Yinping Zhang, Davy Gérard, Jérémie Béal, Mathieu Kociak, Jérôme Plain, Renaud BachelotWhen 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.