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CPP: Chemische Physik und Polymerphysik

CPP 21: Nanoparticles

CPP 21.2: Vortrag

Dienstag, 8. März 2005, 10:00–10:15, TU C243

Third-Harmonic Generation from Individual Gold Nanoparticles: A Size-dependent Nonlinear Susceptibility — •Markus Lippitz, Meindert A. van Dijk, and Michel Orrit — MoNOS, Huygens Laboratory, Universiteit Leiden, P.O. Box 9504, 2300 RA Leiden, The Netherlands

Individual gold colloids with diameters below 100 nm are appealing labels in biophysics because in contrast to normal fluorescent dyes, they neither show photobleaching nor blinking. We report the first observation of third-harmonic signals from individual gold colloids down to 40 nm diameter. Excited with 1-ps pulses at 1500 nm, the colloids generate 500-nm light, close to the plasmon resonance. Furthermore, we found the third-harmonic intensity to vary as the fourth power of the diameter of the colloids, in stark contrast with the sixth-power dependence expected for the nonlinear response of bound electrons. It can be explained by the nonlinear optical response of the free electrons, leading to a size-dependent nonlinear susceptibility. We expect from this size dependence that the use of 100-fs pulses could reduce the detectable colloid size down to 15 nm.