Near-field enhancements of the electric field at the center of spheroidal multilayer metallic nanoparticles (NPs) are investigated when illuminated by focused beams of arbitrary field structure (i.e., amplitude, phase, and polarization distributions). Employing a Mie-type representation, the enhancement at the center of such NPs (such as a core-shell geometry) is analytically shown to be independent of the field structure of the illumination beam for both on- and off-axis NPs. Furthermore, it is shown that, to leading order, the average field enhancement in the near field of these NPs is also approximately illumination independent.
|Number of pages
|Physical Review B - Condensed Matter and Materials Physics
|Published - 22 Oct 2012