Three-dimensional nanofocusing of light through surface plasmon scattering by a lump-like defect in metal/dielectric/metal slot waveguides

We show that scattering of a surface plasmon by lump-like defects on the walls of a metal/dielectric/metal slot waveguide may be accompanied by 3D nanofocusing of light. Such nanofocusing results in the emergence of "hot spots" of nanometer size with a field intensity several orders higher than in the incident plasmon. This effect takes place only if the lump size is smaller than some critical value. We also demonstrate that a so-called plasmonic "black hole" can concentrate electromagnetic energy as well. We believe that the effect of plasmon nanofocusing may be used for plasmonic nanosensing or subwavelength microscopy.