Three-Dimensional Electromagnetic Calculations of Frontal Illumination TERS with a Thin-Film Plasmonic Waveguide...

Tip-enhanced Raman spectroscopy (TERS) is a scanning-probe-microscope-based technique for nanoscale chemical analysis. Recently, we have developed a waveguide TERS probe designed for indirectly illuminating the tops of waveguides to suppress the background signal during TERS measurements. More recently, we have shown that a front-illuminated waveguide probe substantially intensifies the incident light. However, during frontal illumination, the light enhancement principle was previously not fully understood. Therefore, we have investigated the light enhancement mechanism during the frontal illumination of a waveguide probe by three-dimensional electromagnetic calculations, revealing that the signal enhancement principles of directly and nearly directly illuminated waveguide probes are identical and that the TERS contrast is optimized when the intensity of the TERS peak of interest is maximized.