Tip-enhanced optical spectroscopy

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Abstract
Spectroscopic methods with high spatial resolution are essential for understanding the physical and chemical properties of nanoscale materials including biological proteins, quantum structures and nanocomposite materials. In this paper, we describe microscopic techniques which rely on the enhanced electric field near a sharp, laser–irradiated metal tip. This confined light–source can be used for the excitation of various optical interactions such as two–photon excited fluorescence or Raman scattering. We study the properties of the enhanced fields and demonstrate fluorescence and Raman imaging with sub–20 nm resolution.