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Frankfurt 2006 – wissenschaftliches Programm

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Q: Quantenoptik und Photonik

Q 7: Photonik in komplexen und periodischen Strukturen I

Q 7.1: Vortrag

Montag, 13. März 2006, 11:10–11:25, H14

Anisotropic Light Diffusion in Suspensions of Birefringent Colloids — •T. Gisler, K. Sandomirski, G. Maret, and H. Stark — Universität Konstanz, Fachbereich Physik, Fach M621, 78457 Konstanz

We study multiple scattering of light in suspensions of birefringent, spherical colloids with a large, positive birefringence neno≈ 0.2. Due to the anisotropy in the diamagnetic susceptibility, these particles are oriented by a magnetic field B which suppresses the orientation fluctuations.

In the diffusive regime of light transport, the diffuse transmission Td decreases with increasing magnetic field B when the incident wave vector ki is parallel to B. On the other hand, Td measured for kiB increases with B. Furthermore, the particle orientation by the magnetic field leads to a pronounced anisotropy in the transmission profiles when kiB: the photon diffusion coefficient  D perpendicular to the magnetic field is larger than  D||, the photon diffusion coefficient parallel to B, with a maximal value of the anisotropy  D/ D||≈ 1.6 at a magnetic field strength B=7 T. Even at high particle densities and with samples thick enough that ballistic light is virtually absent, we find that the diffusely transmitted light is partially polarized, with a degree of polarization that increases with B and reaches a value 0.14 at B=7 T. This indicates that the orientation of the particles by the magnetic field induces a macroscopic uniaxial symmetry into the random medium guiding the diffusive light propagation.

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