Microscopic surface plasmon enhanced raman spectral imaging

A tightly focused radially polarized beam is employed to excite surface plasmon polaritons (SPPs) on a thin silver film, to form a sharp and strong plasmonic virtual probe at the center. The virtual probe provides a highly enhanced localized electric field with smaller full width at half maximum (~185 nm), demonstrating great potential for Raman spectral detection and high spatial-resolution imaging. Here, an enhanced Raman signal of single-layer graphene is achieved, and its Raman intensity distributions at 2D Raman shifts are obtained by scanning the plasmonic virtual probe, which agrees well with the bright-field image. The system provides a stable Raman detection and imaging technique that can be widely used in fields of Raman spectral analysis.