  We investigate the propagation of surface-enhanced resonant Raman scattering
(SERRS) light by several micrometers through a one-dimensional hotspot (1D HS)
located between a plasmonic nanowire dimer (NWD). The propagation exhibits the
properties, e.g. an effective propagation induced by excitation and detection
polarization orthogonal to the 1D HS long axis, the propagation profiles
composed of bright short and dark long propagations, SERRS spectral shapes
independent of localized plasmon (LP) resonance of NWDs, redshifts in the SERRS
spectra at the edges of 1D HSs, and considerable NWD-by-NWD variations in the
propagation lengths. These properties are well reproduced by numerical
calculations based on electromagnetism. These calculations reveals 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.
