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Scattering and absorption phenomena in translucent materials are usually studied by spectroreflectometric measurements, but can also successfully be investigated by employing a color monitor for translucent materials (CTM). A CTM is a fiber optical instrument which separately detects light which traveled short (Lc) and long distances (Le) in the material under consideration. In this study, the authors qualitatively interpret experimental results by using a Monte Carlo simulation of photon pathways in the material. In this simulation, photons are assumed to be absorbed along the ray path between two scattering events. Scattering is simulated by changes in the photon direction, taking into account the exact phase function for scattering on spherical particles. The boundary conditions imposed are analogous to the experimental situation. Results are presented as the radial distribution of reflected photons, i.e., photons emerging at the plane of incidence. In order to transfer the simulation results to the experimental situation with several more or less randomly oriented fibers, the fiber distribution in the measuring head of the CTM has been characterized by automated image analysis. This fiber distribution has been used to calculate a specific transfer function which enables a theoretical prediction of CTM measurements. Experimental results with monodisperse latex suspensions as well as the model simulations demonstrate the existence of an optimum in the detected Le signal at a specific concentration of the suspension. Discrepancies, however, exist between the experimentally determined and simulated location of the optimum. The simulation model furthermore predicts a highly increasing sensitivity to absorption with increasing suspension concentration. It is concluded that Monte Carlo simulation can be a valuable tool for predicting fiber optical measurements of reflection and absorption phenomena in bulk translucent materials, at least for the Lc signal.
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