Control light propagation and polarization with plasmons for surface-enhanced Raman scattering

摘要

Surface plasmon resonances in metal nanostructures can lead to novel optical properties. The greatly enhanced electromagnetic field makes surface-enhanced Raman scattering (SERS) a highly sensitive spectroscopic technique. We employed Ag nanowires as plasmonic waveguide and achieved remote-excitation SERS at a few molecules level. The junctions between metal nanowires and nanoparticles offer hot spots for SERS, while the enhancement strongly depends on the laser polarization. We studied the polarization dependence in Au nanowire-nanoparticle systems of different geometry. The polarization of Raman-scattered light in SERS is a rarely studied topic. We found nanoantennas composed of a few nanoparticles can manipulate the polarization of emission light. A nanoparticle trimer is the simplest nanoantenna to realize the polarization control. By tuning the position and size of the third particle, emission polarization can be modified in a controllable way. In addition, the refractivity of the surrounding media also plays a crucial role for the emission polarization.