Combining both localized surface plasmon polaritons (LSPPs) and propagating surface plasmon polaritons, remote surface-enhanced Raman scattering (SERS) emerges as a novel sensing technology in recent years, which could avoid the overlap of incident light and inelastic scattering light in SERS. Compared to traditional SERS, it has novel applications in sensors, plasmon-driven surface-catalyzed reactions, Raman optical activity, etc. However, the weak Raman intensity of remote SERS impedes its further application. In this work, we demonstrated that the remote SERS signals could be enhanced by more than 100% through the subwavelength interference in dual-path-excited Ag-branched nanowire dimer and nanowire-nanoparticle systems. Our experiment has revealed that remote SERS intensities could be modulated by polarization and phase differences of two incident lights illuminating at two separate nanowire terminals. The simulated electromagnetic field distributions through the finite-difference time-domain (FDTD) method indicate that subwavelength interference occurs in Ag nanowires, which causes the Raman intensities collected at a remote site is greatly influenced by the coherent superposition of propagating surface plasmon polaritons (PSPPs). Our work on this coherent enhancement could not only promote the application of remote SERS but also enlarge the research on light manipulating in the subwavelength.
Keywords: modulation; nanowires; remote SERS; subwavelength interference; surface plasmons.