Babinet principle for plasmonic antennas: complementarity and differences

Plasmonics deals mainly with surface plasmon polaritons (SPP), which are collective oscillations of free electrons at metal-dielectric interfaces connected with the local electromagnetic field. When SPP are spatially restricted to a metallic nanoparticle, we talk about localized surface plasmons (LSP). LSP resonances can be characterized with an excellent spectral and spatial resolution by electron energy loss spectroscopy (EELS) and cathodoluminescence. Both techniques utilize an electron beam that interacts with the metallic nanoparticle and excites the LSP resonances. EELS measures the energy transferred from electrons to the LSP and cathodoluminescence deals with the light which the LSP emit during their decay. Babinet principle, originating in the wave theory of light and analysis of diffraction, relates the optical response of apertures in thin films and their complementary particle analogues. According to the Babinet principle, LSP in complementary particles and apertures have identical resonance energies and their near fields are closely linked: the electric field distribution of a specific in-plane polarization for an aperture corresponds to the magnetic field distribution of a perpendicular polarization for a particle