Dresden 2003 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 5: Elektronische Eigenschaften von Polymeren
CPP 5.3: Vortrag
Montag, 24. März 2003, 17:30–17:45, ZEU/160
Probing the photonic properties of cholesteric liquid crystals by fluorescent guest molecules — •Jürgen Schmidtke1, Werner Stille1, and Heino Finkelmann2 — 1Physikalisches Institut, Universität Freiburg — 2Institut für Makromolekulare Chemie, Universität Freiburg
Cholesteric liquid crystals (CLCs) are self-assembling 1D photonic crystals with a photonic stop band for circularly polarized light. Circularly polarized fluorescence and band edge lasing of dye doped CLC films have been repeatedly demonstrated. We report on a quantitative model of spontaneous emission in the cholesteric medium, taking into account the photonic band structure and the partial alignment of the emitting molecules due to their anisotropic environment. We find excellent agreement with experimental results1.
CLCs offer a unique way to introduce a defect in the photonic structure: Kopp et al.2 have proposed to generate a localized optical defect mode by a phase jump in the cholesteric helix. We created this defect by stacking two layers of a dye doped polymeric CLC film. We give first experimental proof for an additional resonant mode inside the stop band: the fluorescence spectra show an additional sharp emission peak; pulsed excitation gives rise tolow threshold laser emission. The defect mode emission has a circular polarization whose sense of rotation is opposite to the handedness of the cholesteric helix3.
[1] J. Schmidtke and W. Stille, EPJ B (accepted).
[2] V. I. Kopp, A. Z. Genack, Phys. Rev. Lett. 89, 033901 (2002).
[3] J. Schmidtke, W. Stille, H. Finkelmann, submitted to Phys. Rev. Lett.