Surface Plasmon Field-Enhanced Raman Scattering Co-Excited by P-Polarized and S-Polarized Light Based on Waveguide-Coupled Surface Plasmon Resonance Configuration.

We constructed a waveguide-coupled surface plasmon resonance (WCSPR) structure to enhance Raman scattering. In this structure, P-polarized and S-polarized incident lasers can simultaneously coexcite the evanescent field, thereby further enhancing Raman scattering. This configuration is a five-phase Kretschmann resonance setup that consists of a SF10 prism/inner Ag film/SiO2 film/outer Ag film/water structure. The WCSPR configuration effectively concentrates and confines the evanescent field excited by the incident light. Ag nanoparticles assembled on the outer Ag film surface enhance the evanescent field further by means of surface plasmon resonance. By finely tuning the thickness of the Ag and SiO2 films, it is possible to achieve a coincidence between the SPR angle of P-polarized light and that of S-polarized light. At this angle, both P- and S-polarized light can jointly elevate the evanescent field intensity, leading to the simultaneous enhancement of the electric fields at the upper, lower, left, and right parts of the silver nanoparticles and generating maximum evanescent field enhancement. We achieved an electric field enhancement of up to 103 around the nanoparticles, leading to more SERS hotspots and comparable SERS enhancement capability to gap-type hotspots. Our WCSPR structure combined with the nanoparticles offers a feasible strategy for the SERS detection of large molecules that cannot be placed in traditional gap-type hotspots. It is highly convenient for SERS detection of large molecules.