Determination of the spectral refractive index (RI) and particle size distribution from light scattering measurements

A method is presented to infer simultaneously the wavelength-dependent real refractive index (RI) of microspheres and their particle size distribution (PSD) from extinction measurements in the wavelength range from 260 nm to 1050 nm. To this end we measure the collimated transmittance of a sample suspension in a cuvette using low-divergence white-light illumination and a detection with very low aperture. This serves to collect light only in the forward direction and suppress light scattered at small angles. We compute the ensemble-averaged extinction cross section of the particles, which is then fitted with a model based on Lorenz-Mie Theory and a parametrization of the wavelength-dependent RI with suitable basis functions. In our contribution we present results for RI and PSD determination of micro- and nanoparticle model systems like Poly(methyl methacrylate), polystyrene, and silica and from biological samples, like red blood cells and hemoglobin microparticles.