Far-field control of nanoscale hotspots by near-field interference
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Optical nanoantennas coherently scatter incident optical radiation, creating a localized electromagnetic near-field imprinted with subwavelength phase distribution, rapidly changing in space. The nanostructuring of phase by a nanoantenna makes the scattered field locally interfere with the incident far-field, whose phase lacks nanostructuring and depends only on wave propagation in time and space. Depending on the resonance conditions and material properties, the interference strongly modifies the resultant near-field intensity of the nanoantenna. Here, we present direct imaging of the local near-field interference effect in the near-field of a resonant dipole nanoantenna, supported by numerical calculations. We use single fluorescent emitters as local detectors to map the field distribution of nanoantennas with nanometer precision in the presence of an incident field. Taking advantage of the dipole orientation of the molecule we probe the vectorial character of the near-field interference map. Exploiting the local interference we demonstrate position control of the localized field, i.e., the plasmonic hotspots in the near-field of a nanoantenna. The results shown in this paper are important for applications where the enhancement and precise hotspot position at the nanoantenna are crucial, such as in high-resolution fluorescence imaging. Moreover, the interference effect can be exploited to shape the nanoantenna near-field to produce a tailored optical response such as polarization-controlled nanoscale hotspot switching, as we show here.
CitationSingh, A. [et al.]. Far-field control of nanoscale hotspots by near-field interference. "ACS Photonics", 31 Juliol 2020,