MODELING OF THE EFFECT OF MULTIPLE-SCATTERING IN PHOTON-CORRELATION SPECTROSCOPY - PLANE-WAVE APPROACH

A technique for numerical modeling of the time autocorrelation functio n (ACF) of the electric field scattered from a concentrated dispersion , which is illuminated by a plane wave, has been developed as an appro ach to estimate the particle dynamics and multiple scattering effects in photon correlation spectroscopy measurements. Systematic error of t he modeling of the particle dynamics and the error of the ACF estimati on were investigated for Brownian free particles. It has been found th at systematic error and the decreased dynamic delay-time range of the ACF exponential behavior for free particles are caused by low- and hig h-frequency oscillations of integrated functions. An optimization of t he numerical model has been carried out in order to reach a required m agnitude of the systematic error and a maximum of the dynamic delay-ti me range by a minimum of calculation expenditures. The dynamics of an ensemble of particles was generated by a stochastic technique. Practic al application of the proposed technique was shown by modeling of the first-order ACF for the depolarized component of the backscattered ele ctric field. Influence of multiple-scattering by interacting spheres o n this ACF was investigated for different sphere diameters and dispers ion concentrations by using a rigorous multiple-scattering technique. This model can be used to further develop photon correlation spectrosc opy for the characterization of particles in concentrated and turbid m edia: in a following paper, the multiple-scattering suppression by one -beam cross correlation is simulated, taking into account geometrical parameters of a setup.