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Tip-enhanced near-field CARS microscopy for molecular nano-imaging

Optical microscopy that can visualize the molecular vibration with a nanometric spatial resolution has been realized by a combination of near-field optics and coherent anti-Stokes Raman scattering (CARS) spectroscopy. A metallic probe with a sharp tip is used to strongly enhance optical near-field in the local vicinity of the tip owing to the excitation of local surface plasmon polariton. CARS signals of molecules in the local area can be strongly induced by the plasmonic field. We have visualized DNA molecules and single-walled carbon nanotubes (SWNTs) with a spatial resolution far beyond the diffraction limit by the tip-enhanced near-field CARS microscopy.