Surface-enhanced Raman scattering at a planar dielectric interface beyond critical angle.

Light refraction at the planar boundary of dielectric media prevents light propagation in the higher refractive index medium at angles beyond the critical value. This limitation is lifted when the evanescent wave is excited at the lower refractive index side of the interface. In this work we quantify polarization and angle dependence of surface-enhanced Raman scattering (SERS) intensity beyond the critical angle. Specifically, Raman spectra of thiocyanate molecules adsorbed on clustered silver nanoparticles at the water-glass interface were acquired using evanescent excitation and detection. Detected SERS signal polarization and scattering angle dependence are shown to be in agreement with a simple model based on excitation and radiation of a classical dipole near a lossless interface.