Polarization-selective mapping of near-field intensity and phase around gold nanoparticles using apertureless near-field microscopy

Enhanced near-field distributions around a single gold nanosphere are imaged using scattering-type apertureless near field scanning optical microscopy (ANSOM) at a wavelength of 632.8 nm. For the first time, polarization-selected ANSOM images are obtained that show both the transverse (perpendicular to the tip axis) and the longitudinal (parallel to the tip axis) vector components of the near-field in a phase sensitive manner. A model calculation using a Green's dyadic propagator method successfully reproduces the features of the observed intensity and phase images, providing an interpretation of the ANSOM images. The results open up the possibility that the field vector directions as well as the field magnitude around plasmonic nanostructures and nanodevices can be directly mapped using the ANSOM technique.