Mapping three-dimensional near-field responses with reconstruction scattering-type scanning near-field optical microscopy

Scattering-type scanning near-field optical microscopy (s-SNOM) enables mapping of nanoscale field distributions in two dimensions. However, the standard s-SNOM technique lacks direct resolving ability along the vertical direction, therefore unable to provide full three-dimensional near-field responses. Here, we develop a reconstruction technique that enables s-SNOM to collect a three-dimensional response cube of near-field interaction. The technique also allows a new operational mode of s-SNOM based on the characteristic decay range of near-field interactions. As a demonstration, the bound near-field at the sides of a polaritonic boron nitride nanotube is revealed through the collection of the near-field response cube. The graphene boundary and discontinuities are revealed by the near-field decay range mapping. The reconstruction s-SNOM technique extends the capability of s-SNOM and is generally applicable for a wide range of nanoscale characterizations that are suitable for s-SNOM, such as characterizations of plasmonic and polaritonic nanostructures.