Near-field photonics: tip-enhanced microscopy and spectroscopy on the nanoscale

Any detailed study of the interaction of electromagnetic radiation with nanoscale systems is limited by diffraction effects in classical optical systems. Near-field microscopy extends conventional imaging beyond this self-imposed barrier and is used to perform microscopy and spectroscopy with ultra-high spatial resolution. In this article we will discuss the use of the enhanced electric field created at the apex of a sharp laser-irradiated metal tip as a means of producing a truly nanoscale light source. This confined light source can be used to excite locally vibrational modes along carbon nanotubes or to investigate surface charge oscillations in optically resonant nanoparticles. We report the use of such a technique to demonstrate localized photofluorescence and Raman imaging with sub 20 nm spatial resolution.