Excitation and propagation of surface plasmons on metallic nanowires

The comprehensive understanding of the excitation and propagation of surface plasmons (SPs) on metallic nanowires (NWs) is essential for potential applications of these materials as nanoscale optical waveguides. Combining theory and different experimental methods, we did intensive study on the excitation and propagation of SP modes in crystal Ag nanowires. We found the excitation of NW SP modes is strongly affected by the excitation configuration. When an optically "thick" NW is radiated at the end of the NW, several SP modes could be excited simultaneously with appropriate incident polarization. If the NW is in the medium of uniform refractive index, the coherent superposition of these SP modes generates chiral SPs in single NW, and the handedness of the chiral SPs can be controlled by the input polarization angle. When we use a near field scanning optical fiber tip to excite the SPs on metallic nanowires from the middle of the NW, we also found multiple SP modes in the NWs can be excited through polarization selective near field interaction. The excitation mechanism of the tip-induced SP propagation is quite different from the previous wire-end-launching scheme. We found the input coupling efficiency is modulated by Fabry-Perot interferences in the near field coupling case.