Berlin 2015 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 12: Optical and Nonlinear Optical Properties I (DF with CPP)
DF 12.3: Vortrag
Mittwoch, 18. März 2015, 10:20–10:40, EB 407
Whispering Gallery Modes in Single Copolymer Microspheres — •Daniel Braam1, Kenichi Tabata2, Soh Kushida2, Robert Niemöller1, Günther M. Prinz1, Yohei Yamamoto2, and Axel Lorke1 — 1Faculty of Physics and CENIDE, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany — 2Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
Copolymers are promising candidates for use in optoelectronic devices due to their low fabrication cost and high emission efficiency. Here we investigate several π-conjugated alternating copolymers, which combine the advantages of being a dye, a dielectric and a self-assembled resonator, as they form nearly perfect spheres when precipitated from solution. Excitation leads to standing waves inside these microspheres, known as whispering gallery modes (WGMs). Their spectral position, number and line width is dependent on the sphere diameter. The measurements, showing both TM- and TE-modes, are in good agreement with model calculations [1]. The relative amplitude of the modes is strongly dependent on the sphere’s excitation spot, revealing leakage of polar modes to the substrate, while equatorial modes sustain. During continuous illumination we observe lifting of degeneracy of the WGMs, followed by slow deterioration. Covering the spheres with a thin layer of titanium leads to an improved resistance against irradiation damage.
[1] Tabata, K., Braam, D. et al. Self-assembled conjugated polymer spheres as fluorescent microresonators. Sci. Rep. 4, 5902; DOI:10.1038/srep05902 (2014).