Ultrafast Dynamics of metallic nanorod arrays and their interaction with quantum dots and dye molecules

• Applicant: Privatdozent Dr. Stefan Grafström
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2010 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 167205761

This project focuses on the optical properties of two-dimensional arrays of metal nanorods standing perpendicular to a substrate and of hybrid systems consisting of such arrays filled with semiconductor quantum dots (QDs) or organic dye molecules. The optical properties of the metal structure are governed by surface plasmon resonances (SPRs), with the coupling between the individual rods leading to a more complicated spectrum than known from isolated nanorods. Furthermore, the nanorod array shows unusual optical phenomena such as all-angle negative refraction of the Poynting vector. It is the aim of this project to develop a profound understanding of the response of metal nanorod arrays to femtosecond optical excitation. By means of transient-transmission measurements (preliminary experiments have shown transient changes in transmission as large as 40%!) the relaxation of the surface plasmons by electron-electron, electron-phonon, and phonon-phonon interaction will be studied for the various SPRs and under variation of the geometry of the nanorod array. Special attention will be paid to the ultrafast processes. Finally, the dynamics of QDs or dye molecules in close proximity to the nanorod structures will be investigated to improve the understanding of the energy transfer between surface plasmons and two-level systems. In particular, we will search for the onset of “spasing”, i.e., the analog of lasing with the metal structure playing the role of the resonator and the QDs or dye molecules being the gain medium The experimental work will be accompanied by detailed numerical modeling.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Karl Leo