Scanning near-field optical microscopy with white-light illumination: nanoscale imaging and spectroscopy of resonant systems

We present the realisation of near-field spectroscopic measurements with fibre-tip-based scanning near-field microscopy. It allows simultaneous acquisition of near-field optical images in a broad spectral range (400 nm to 1000 nm), thus recovering local spectroscopic information. The technique is essential for understanding the resonant interaction of light with nanostructured objects as the far-field and near-field spectral response can differ significantly, e.g., in the case of plasmonic nanostructures. By mapping the evanescent fields, the approach also provides spectroscopy technique with nanoscale spatial resolution. Several applications of spectroscopic near-field microscopy are described for visualisation of plasmonic modes in metallic nanostructures and near-field fluorescence spectroscopy.