Figure 2: Mapping surface plasmon standing-waves with gap mode SERS imaging.
From: Mapping plasmonic near-field profiles and interferences by surface-enhanced Raman scattering
(a) Measured plasmonic near-field distribution produced by a tightly-focused radially polarized beam (RPB) (a1), compared with the calculated perpendicular (a2) and in-plane (a3) electric field components. (b) The corresponding mappings of surface plasmon fields generated under a tightly-focused linearly polarized Gaussian beam (LPGB) (b1), a circularly polarized beam (CPB) (b2) and a linearly polarized optical-vortex beam (LPVB) of charge “1” (b3), to verify further the perpendicular field sensitivity of our method and the RPB capability to produce a strongly confined perpendicular field at the center. (c) Cross-section comparison between measured plasmon field (a1) and calculated perpendicular field component (a2). (d) Statistical measurement of the lateral field-extension of the central spot with 50 randomly-selected nanospheres on the metal film, verifying accuracy and reproducibility of our measurement. Incident wavelength is 532 nm in all cases. Area of each contour map is 4 μm×4 μm.
