Accurate identification of the spectral complex refractive index and particle size distribution in participating media using an ant colony algorithm

In this study, we attempted to apply the ant colony algorithm (ACO) based on probability density function (PDF) to the retrieval of optical constant and particle size distribution (PSD) for a particulate system. A secondary optimization technique was introduced that allows the optical constant and PSD to be retrieved simultaneously by measuring the diffuse transmittance (T), diffuse reflectance (R), and collimated transmittance (Tc). It was found that the PSDs were relatively insensitive to the diffuse reflectance and transmittance, which was taken advantage of in the inverse procedure. Three commonly-used PSD functions, i.e., the Rosin-Rammer function, the standard Normal function and the Logarithmic Normal function, were applied to evaluate the performance of the PDF-based ACO algorithm and the secondary optimization technique. In conclusion, the present work deals with the problem that traditional available techniques cannot obtain the optical constant and PSDs simultaneously. A secondary optimization technique that involves PDF-based ACO algorithm was developed. The proposed technique has the advantage of only requiring simple measurement equipment. Results show that the optical constant and PSDs can be estimated accurately and simultaneously.