Propagation mechanism of surface plasmons coupled with surface-enhanced resonant Raman scattering light through a one-dimensional hotspot along a silver nanowire dimer junction

We investigate the propagation of surface-enhanced resonant Raman scattering (SERRS) light coupled with surface plasmons (SPs) by several micrometers through a one-dimensional hotspot (1D HS) located between a plasmonic nanowire dimer (NWD) by end-type excitations. The propagation exhibits properties, e.g., an effective propagation is induced by excitation and detection polarization orthogonal to the 1D HS long axis, the propagation profiles are composed of bright short and dark long propagations, SERRS spectral shapes are independent of localized plasmon (LP) resonance of NWDs, the SERRS spectra redshifts at the edges of 1D HSs, and considerable NWD-by-NWD variations appear in the propagation lengths. These properties are well reproduced by numerical calculations based on electromagnetism. These calculations reveal the following propagation mechanism: excitation light resonantly coupled with LP at the edges of 1D HSs, and the light energy is transferred to two types of junction SP modes supporting the short and long propagations; these modes are attributed to the upper and lower branches of coupled two-SP modes. This mechanism comprehensively clarifies the abovementioned properties.