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Currently, several disciplines of science are merging into the "Nano-World", the size regime between 1 micron and 10 Angstrom. This is the size regime where things get too complicated to be explained from scratch, i.e. by quantum mechanics, but are also far from our macroscopic experience.

There are many ways to access this size regime. The one we chose is by optical means. This includes single gold nanoparticle spectroscopy [1,7], temporally [3] and spectraly [4] resolved spectroscopy of fluorophores close to gold nanoparticles, and time resolved spectroscopy of semiconductor nanoparticles [5,6]. Three dimensional imaging beyond the diffraction limit is an other important tool in nanophotonics[2]. An important field of applications of nanoparticle spectroscopy is in biosensing [7,8].

In a recent collaboration with Prof. Vladimir Shalev, we investigate metamaterials that contain noble metal nanostructures and provide a negative refractive index at visible frequencies. It is of utmost importance to fight losses in negative index metamaterials in order to achieve reasonable working devices in the future [9].

[1] Surface-Plasmon Resonances in Single Metallic Nanoparticles
T. Klar, M. Perner, S. Grosse, G. von Plessen, W. Spirkl and J. Feldmann
Physical Review Letters 80, 4249 (1998).

[2] Fluorescence microscopy with diffraction resolution barrier broken by stimulated emission
T. A. Klar, S. Jakobs, M. Dyba, A. Egner and S. W. Hell
Proc. Natl. Acad. Sci. USA (PNAS), 97, 8206-8210 (2000)

[3] Fluorescence Quenching of Dye Molecules near Gold Nanoparticles: Radiative and Nonradiative Effects
E. Dulkeith, A. C. Morteani, T. Niedereichholz, T. A. Klar, and J. Feldmann, S.A. Levi, F. C. J. M. van Veggel, D. N. Reinhoudt, M. Möller, D. I. Gittins
Physical Review Letters 89, 203002 (2002)

[4] Shaping emission spectra of fluorescent molecules with single plasmonic nanoresonators
M. Ringler, A. Schwemer, M. Wunderlich, A. Nichtl, K. Kürzinger, T. A. Klar, and J. Feldmann
Physical Review Letters 100, 203002 (2008)

[5] Self-Assembled Binary Superlattices of CdSe and Au Nanocrystals and their Fluorescence Properties
E. Shevchenko, M. Ringler, A. Schwemer, D. V. Talapin, T. A. Klar, A. L. Rogach, J. Feldmann, P. Alivisatos
Journal of the American Chemical Society (JACS) 130, 3274 (2008)

[6] Exciton Recycling in Graded Gap Nanocrystal Structures
T. Franzl, T. A. Klar, S. Schietinger, A. L. Rogach, and J. Feldmann
Nano Letters 4, 1599 (2004)

[7] Biomolecular Recognition Based on Single Gold Nanoparticle Light Scattering
G. Raschke, S. Kowarik, T. Franzl, C. Sönnichsen, T. A. Klar, and J. Feldmann, A. Nichtl and K. Kürzinger
Nano Letters 3, 935 (2003)

[8] Gold NanoStoves for Microsecond DNA Melting Analysis
J. Stehr, C. Hrelescu, R. A. Sperling, G. Raschke, M. Wunderlich, A. Nichtl, D. Heindl, K. Kürzinger, W. J. Parak, T. A. Klar, J. Feldmann
Nano Letters 8 (2), 619 (2008)

[9] Negative-Index Metamaterials: Going Optical
Thomas A. Klar, Alexander V. Kildishev, Vladimir P. Drachev, and Vladimir M. Shalaev,
IEEE Journal of Selected Topics in Quantum Electronics, 12, 1106 (2006)