Wednesday February 2, 2005
4 PM
PHO 339

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"Surface Plasmon-Optics from 2 to 0 Dimensions: From Stimulated Plasmon Emission to Scattering Near-Field Optics in Optically Anisotropic Samples"
Lukas M Eng
Dresden University of Technology

We report on our recent activities investigating surface plasmon polaritons (SPP) in 2-dimensional and O-dimensional nanostructures. SPPs confined to thin Ag metal film were subjected to reflection and transmission when scattered from a nanoscaled groove machined into the film by focused ion beam. Both the amount of reflected and transmitted light may elegantly be tuned by changing the groove width and film thickness. Moreover, the transmission behaves non-monotonic in that unless quantum mechanical tunnelling for electrons, “magic” groove widths allow efficient optical transport across the groove.

Second, we show, for the first time, that pumping fluorescent molecules, deposited onto the thin metal film may efficiently couple to a propagating SPP. The choppered measurements indicate that it is possible to obtain gain via stimulated emission of Plasmons. This may possibly open the way to surface plasmon amplification.

Third, the 2-dimensional metallic film will be replaced by a 2D cluster array being deposited via a co-polymer micelle technique. Spherical clusters of ~ 12 nm diameter and a spacing of up to 200 nm have been created. Most interestingly, the propagating SPP behaves practically equal to SPP transport in the solid 2D metal film; the decay length measures > 25 µm as deduced with near-field scanning optical microscopy (NSOM) using a dielectric tip. In addition, the 2D cluster array was inspected in a TIRF set-up, giving clear evidence that the variability in diameter and spacing of the 2D cluster array allows to tune the optical band structure considerably. Finally, the concept of SPP will be discussed for 0-dimensional nanostructures such as individual clusters or tips from a scattering NSOM for the case of investigating optically anisotropic samples. We show that the optically backscattered light in such an experiment shows a non-trivial and very complicated behaviour that can no-longer be explained in a simple image-dipole scenario. Beyond the material contrast due to the variable dielectric constant e, the tensorial properties e give rise to anisotropic surface reflection, as well as to the sheet charges developing into the bulk of the anisotropic sample.

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