Last years, the quickly developing field of artificial optical meta- and plasmonic materials is demanding a technique capable of imaging the magnetic field of light, in addition to the traditionally measured electric field. Scanning near-field optical microscopy (SNOM) allows sub-wavelength mapping of different field components, by scanning different probes in the near-field of a sample.
In our work, we first experimentally demonstrate and confirm by numerical simulations, that the hollow-pyramid aperture probe SNOM can be used to image the lateral magnetic field of light in simple plasmonic antennas – rod, disk, ring. We suggest that this probe can be first-order approximated by a magnetic point dipole source. This considerably reduces the simulation time and complexity and facilitates the interpretation of the near-field images. Then, we use the validated technique to study the magnetic near-field distributions of geometrically more complex plasmonic antennas – L-, C-, G- shapes, etc. Notably, the near-fields of the studied complex resonators are a superposition of the individual constituting elements’ near-fields. This opens up new possibilities for engineering and characterization of complex plasmonic antennas.
Thus, the implemented hollow-pyramid aperture SNOM technique complements the currently existing techniques for imaging the different electromagnetic field components and contributes to the complete characterization of nanoscale devices, by now providing an opportunity to explore magnetic light-matter interactions with sub-wavelength resolution.