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We describe the employment of a novel light-scattering scheme for the decorrelation of multiple scattering in strongly turbid samples. The three-dimensional scheme, which has been proposed already theoretically, shows certain advantages compared with the two-colour apparatus, which is commercially available. We describe our set-up in detail; features are the use of modern semiconductor laser diodes and contemporary single-mode ®bre receivers. We show experimentally that the optimal signal-to-noise ratio (or intercept) optˆ0 :20, which is obtainable with our set-up, can be quantitatively calculated from the measured uncertainties in the alignment. In particular, we give a detailed derivation of all factors in¯uencing the signal-to-noise ratio. We investigate a highly turbid polystyrene latex sample with a nominal radius of 57.5 nm and 5% solid content, to demonstrate clearly measurements of the cross correlation function without distortions due to multiple scattering. With its turbidity of 3 mm ¡1 at 790 nm this represents the most turbid sample which has been investigated by dynamic light scattering to date.

In view of time correlated photon-counting experiments using wavelengths at the red end of the electromagnetic spectrum, we developed a simple electronic circuit for periodical gated quenching of silicon avalanche photodiodes. We compare the performance of this device with commercially available passive and active quenching modules and a reference photomultiplier. The detection system’s nonlinearities, i.e., dead time and afterpulsing, lead to direct and indirect distortions of photocount correlation functions. We characterize this nonlinear behavior by measuring intensity auto- and cross-correlation functions and supply nonlinearity parameters for each of the four detection systems. In addition, transfer functions are given which allow an estimate for the highest count rates accessible for each detection system.

Theoretical calculations for colloidal charge-stabilized suspensions and hard sphere suspensions show that hydrodynamic interactions yield a qualitatively different particle concentration dependence of the short-time self-diffusion coefficient. The effect, however, is numerically small and hardly accessible by conventional light scattering experiments.Applying multiple-scattering decorrelation equipment and a careful data analysis we show that the theoretical prediction for charged particles is in agreement with our experimental results from aqueous polystyrene latex suspensions.

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