Abstract

A measurement and data evaluation technique for the separate determination of the scattering and absorption properties of loose pharmaceutical powders is described. The equation of radiative transfer for diffuse reflectance and transmittance is analytically solved by using a three-flux approximation. Combined transmittance and reflectance measurements then allow one to derive both the scattering and the absorption coefficients. The scattering and absorption coefficients provide more information about particle size, degree of agglomeration, and chemical composition of the samples in comparison to the usual determination of only the ratio of the coefficients from diffuse reflectance measurements on optically thick samples. Furthermore, the theory of diffuse reflectance of optically thick samples according to Kubelka and Munk is compared to the three-flux approximation. The influence of the particle size on the scattering and absorption coefficient is investigated, and it is shown that the assumption of a wavelength-independent scattering coefficient, though often made in reflectance spectroscopy, is not generally valid.

Determination of the Optical Absorption Coefficient of Powdered Materials Whose Particle Size Distribution and Refractive Indices Are Unknown

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Determination of Absorption and Scattering Coefficients for Nonhomogeneous Media. 2: Experiment

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Appl. Opt. 12(8) 1816-1823 (1973)

Visible spectral dependence of the scattering and absorption coefficients of pigmented coatings from inversion of diffuse reflectance spectra

Fernando Curiel, William E. Vargas, and Rubén G. Barrera
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Absorption-sensitive diffuse reflection imaging of concealed powders using a terahertz quantum cascade laser

Paul Dean, Muhammad U. Shaukat, Suraj P. Khanna, Subhasish Chakraborty, Mohammad Lachab, Andrew Burnett, Giles Davies, and Edmund H. Linfield
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Two-flux radiative transfer model under nonisotropic propagating diffuse radiation

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