Surface-enhanced Raman spectroscopy based on plasmonic slot waveguides with free-space oblique illumination

In our quest to demonstrate an all-on-a-chip Raman spectrometer, we are reporting a configuration that strongly suppresses background noise typical of the SiN photonics waveguides. We use an excitation of a plasmonic waveguide that is oblique so that the molecules within the plasmic waveguides are Raman excited but the pump light is not properly coupled to the waveguide but only slightly scattered. As only scattered light is coupled to the collecting SiN waveguide, the pump-induced background photon noise is highly suppressed. Moreover, the plasmonic structure and the incidence angles are engineered so that there is a resonant enhancement thus boosting further the field of the pump beam.