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The accuracy of optical simulations including bulk diffusors is heavily dependent on the accuracy of the bulk scattering properties. If no knowledge on the physical scattering effects is available, an iterative procedure is usually used to obtain the scattering properties, such as the inverse Monte Carlo method or the inverse adding-doubling (AD) method. In these methods, a predefined phase function with one free parameter is usually used to limit the number of free parameters. In this work, three predefined phase functions (Henyey-Greenstein, two-term Henyey-Greenstein, and Gegenbauer kernel (GK) phase function) are implemented in the inverse AD method to determine the optical properties of two strongly diffusing materials: low-density polyethylene and TiO₂ particles. Using the presented approach, an estimation of the effective phase function was made. It was found that the use of the GK phase function resulted in the best agreement between calculated and experimental transmittance, reflectance, and scattered radiant intensity distribution for the LDPE sample. For the TiO₂ sample, a good agreement was obtained with both the two-term Henyey-Greenstein and the GK phase function.

Diffusors are widely used optical components having numerous applications. They are commonly used to homogenize light beams and to create particular intensity distributions. The angular scattering profile of bulk scattering diffusing materials is determined by three bulk scattering parameters that are, however, not commonly available. This hampers an accurate implementation of bulk diffusors in ray tracing simulations. In this paper, the bulk scattering parameters of a concentration series of milk diluted with water were determined with the inverse adding-doubling method. Using these values as input, the macroscopic angular scattering profile was simulated using ray tracing software. The simulation results were compared to experimental data, and a good agreement between measured and simulated data was found. The method was also proven to be successful when applied to commercial diffusors.