Pulp consists of distinguishable particles, the refractive indices of which differ from the index of the employed medium,
water. We are thus dealing with an optically scattering material. Particle distribution in pulp is nowadays a focus of
interest. This parameter is related to the photon path length distribution (PPLD) determined by the inhomogeneity of the
scatterer. In order to assess PPLD, we use two methods. In the first, the particle properties in pulp are estimated by
means of a microscope. A model for Monte Carlo simulation is then built to obtain PPLD. In the second, the signal
generated by a laser pulse passing the cuvette filled with water or pulp is detected with a streak camera and the
assessment of PPLD accomplished by a deconvolution procedure. To obtain the particle distribution, the two methods
may be used together, so that the streak-camera measurements give PPLD, and in the following simulation process the
particle distribution is found, which corresponds to the determined PPLD. The number and diversity of the sample sets
currently used do not fulfill the statistical requirements of the industry. Nevertheless, the results achieved encourage us to
develop the methods further.
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