Dresden 2006 – wissenschaftliches Programm

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O: Oberflächenphysik

O 6: Scanning probe techniques I

O 6.5: Vortrag

Montag, 27. März 2006, 12:15–12:30, WIL B321

Nonlinear nano-optics: tip-enhanced spectroscopy based on optical frequency conversion at a metal tip — •Matthias Danckwerts, Michael Beversluis, and Lukas Novotny — Institute of Optics, University of Rochester, Rochester NY 14627 (USA)

At a sharp gold tip illuminated with pulsed laser light at 800 nm, the interaction of the electromagnetic field with the metal leads to the generation of frequency-doubled light as well as a supercontinuum arising from 2-photon excited interband transitions. In the case of multi-wavelength illumination, mixing signals such as DFG and SFG and higher-order processes like 4-wave mixing are observed. Due to the local field enhancement, the source of this radiation is highly confined to within nanometers at the apex of the tip, hence the tip is acting as a nanometric light source.

This offers a range of nanoscopic optical spectroscopies, where the tip acts as a source, not as a scatterer of light emitted from an object. The measured light is spectrally well-separated from the excitation, allowing for essentially background-free detection. For an application, we show optical extinction measurements with a lateral resolution of 30 nm. Further, experiments utilizing the continuum radiation from the tip for elastic scattering measurements at nanostructures such as carbon nanotubes are discussed.