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Q: Fachverband Quantenoptik und Photonik

Q 49: Laseranwendungen: Laserspektroskopie

Q 49.4: Vortrag

Donnerstag, 17. März 2011, 11:15–11:30, SCH A215

(contribution withdrawn) Direction-selective optical limiting in bi-layer glass-metal nanocomposites — •Sabitha Mohan and Gerhard Seifert — Physics Institute, Martin-Luther-Universität Halle-Wittenberg, von-Danckelmann-Platz 3, 06120 Halle (Saale)

We have studied the optical nonlinearity of a glass-metal nanocomposite containing spherical silver nanoparticles in a thin surface layer of a few micrometers only. The remainder of the sample thickness of 1 mm consists of the pure soda-lime glass substrate. Femtosecond z-scan experiments have been performed using a Ti:Sa laser (wavelength λ=800nm, pulse duration τ=80fs, repetition rate 1kHz) as excitation source. This wavelength is suited for two-photon absorption by the Ag nanoparticle’s surface Plasmon resonance (at 410nm), while the glass UV absorption requires at least three photons to be absorbed simultaneously. Irradiating the sample first from the substrate, then from the particle layer side, we found a highly directionally selective nonlinear transmission. When the laser beam enters the sample from the substrate side, the nonlinear absorption is enhanced by five orders of magnitude compared to irradiation from the particle side. It is shown by careful theoretical modelling that this optical diode-like behaviour can be explained by self-focusing effects in the glass substrate. In one direction, the pertinent intensity increase upon passing the substrate leads to strongly enhanced two-photon absorption in the particle layer; while in the other direction three-photon absorption in the glass remains negligible.