Lisa Aberle

Effective suppression of multiply scattered light in static and dynamic light scattering

The evaluation of conventional light-scattering experiments in turbid media is often highly complicated because of the presence of multiple scattering contributions. The three-dimensional (3-D) cross-correlation method presented provides an effective and handy method to suppress the influence of multiply scattered light. As the time dependence of the 3-D cross-correlation function is determined solely by the singly scattered light, the evaluation of the decay constant yields reliable values for the effective diffusion coefficient and the hydrodynamic particle size of the suspended particles. Furthermore, analysis of the amplitude of the 3-D cross-correlation function permits the determination of the differential scattering cross section even for highly turbid suspensions.

A comparison of 3D static light-scattering experiments with Monte Carlo simulations

The problems arising in conventional static light-scattering experiments with turbid samples due to multiple scattering of light can be overcome by the cross correlation technique. We recently reported results of 3D cross correlation experiments in which the angle dependence of the experimentally determined values of the singly scattered light intensity agrees with that of the scattering cross section of the suspended particles. In this paper we present measurements for various optical path lengths of the scattered light and compare the experimental results with Monte Carlo simulations. We demonstrate that the dependences of the singly and multiply scattered light intensities on the optical path length obtained by the 3D cross correlation method are in good agreement with the data obtained from Monte Carlo simulations. These results further confirm that the 3D cross correlation technique indeed allows the direct determination of the singly scattered light intensity by experimental means without any need for the detailed information about the experimental set-up that is necessary in Monte Carlo simulations.

Experimental determination of singly scattered light close to the critical point in a polystyrene–cyclohexane mixture

In turbid media the presence of multiple scattering constitutes a major complication for the analysis of the intensity and of the intensity correlation functions of the scattered light. The 3D-cross-correlation technique provides an effective means to determine the single scattering intensity and to suppress the influence of multiple scattering to the time dependence of correlation functions. The technique is applied to study the temperature dependence of the critical fluctuations of a solution of polystyrene (Mw=1.11×105 g mol-1) in cyclohexane. We show that the single scattering intensity determined for a scattering angle of ϑ=90° can be described by the Ornstein–Zernike function over the entire temperature range of 313.15–293.49 K. Good agreement between experiment and Monte Carlo simulations of the scattering processes is found for the ratio of singly scattered light to the total scattering intensity.

Three-dimensional cross correlation technique: influence of multiply scattered light in the Rayleigh–Gans regime

The correct interpretation of light scattering data requires knowledge of the extent to which multiple scattering contributes to the measured signal. Generally, this information cannot easily be obtained in conventional light scattering experiments. We demonstrate the difficulties which arise with this problem by experiments with scatterers where the differential scattering cross section does not exhibit scattering minima. We investigate the influence of multiple scattering by performing combined static and dynamic light scattering experiments using the 3D cross correlation technique. We discuss that, despite the increase of the intensity ratio of multiply to singly scattered light with increasing scattering angle, the dynamic properties are more strongly affected for small scattering angles.