Complex refractive index of nonspherical particles in the visible near infrared region: application to Bacillus subtilis spores

Abstract

A method is presented for the estimation of optical constants in the ultraviolet-visible-near-infrared (UV-Vis-NIR) region of nonspherical particles in a suspension at concentrations where multiple scattering is significant. The optical constants are obtained by an inversion technique using the adding-doubling method to solve the radiative transfer equation in combination with the single scattering theories for modelling scattering by nonspherical particles. Two methods for describing scattering by single scattering are considered: the T-matrix method and the approximate but computationally simpler Rayleigh-Gans-Debye (RGD) approximation. The method is then applied to obtain the optical constants of Bacillus subtilis spores in the wavelength region 400-1200 nm. It is found that the optical constants obtained using the RGD approximation matches those obtained using the T-matrix method to within experimental error.