Near-field fluorescence imaging by localized field enhancement near a sharp probe tip

This work describes near-field investigations of luminescent nanosamples based on monitoring fluorescence due to the enhanced field around a laser-illuminated probe tip. These fluorescence effects are investigated as a function of probe-sample separation, which identify a strong, spatially localized (≈7 nm) enhancement of the incident laser field in the vicinity of the probe tip. From a model fit to the fluorescence data, the localized enhancement of the electric field is estimated to be >tenfold, which predicts a significant increase in localized excitation intensity (> 100-fold) for fluorescence imaging of molecular size samples.