Hemispherical factors of model random-scattering composite materials

We present an optical experimental study, in the visible and the near infrared, of three-dimensional random composite materials made of pellets of KBr filled with Ge particles with mean radius a = 5 microm. We measure hemispherical factors (transmittance and reflectanc6) on composite materials with various concentrations in a wavelength range between 0.3 and 1.8 microm. We discuss the results by using both the properties of single scatterers, and the radiative transfer theory for modeling multiple scattering in concentrated samples. Because of the high asymmetry factor for scattering of the Ge particles, we can assume that photons are scattered in only two directions, backward and forward, and we show that a simple two-stream theory is adequate for interpreting the main results as functions of both wavelength and composition, without any adjustable parameters.