Coherent Backscattering from Multiple Scattering Systems - KOPS ...

6 Summary
D = 13300 m2 /s. This agrees pretty well with results of measurements with the old setup and
with the results of the wide angle experiments, which yield correct results if the diffusion
coefficient obtained with the small angle setup is used for the evaluation. With these findings
the reliability of the results of the small angle setup is confirmed.
Another application for the small angle setup was to determine the transport mean free path
of fluidized beds. As the scattering particles in these experiments are rather large and have a
regularly spherical shape, the intensity distribution of the backscattered light is superimposed
by the ring structure of the single scattering on the Mie particles. This structure can however
be calculated theoretically and adapted to the measured curves, so that the backscattering
cone can be extracted from the data.
In first measurements the width of the backscattering cone led to a transport mean free path
that was significantly shorter than the particle diameter of the scatterers. This is in strong
contrast to the results of similar experiments, which are reported to be of the order of several
particle diameters. The reason for this is still under discussion; however, the basic procedure
for the evaluation of the backscattering data of fluidized beds was tested successfully.
For future experiments, the combination of the two revised backscattering setups offers the
unique possibility to measure kl ∗ over more than three decades, from samples at the transition
to Anderson localization at kl ∗ ≈ 1 to weakly scattering samples with extremely narrow
backscattering cones. Possible applications range from experiments on new, custom designed
particles with small kl ∗ to measurements on foams or biological tissue. Some of these experiments
are already planned for the near future, and will hopefully provide a step further
towards fully understanding multiple scattering.
70