Fluorescence scattering in between excitation and emission as a depolarizing process: a Mueller matrix viewpoint.

Abstract

A rigorous model has been proposed to qualify fluorescence scattering through the Mueller matrix viewpoint in terms of absorption/excitation, emission, and the process in between them. The process in between the excitation and emission processes of fluorescence, irrespective of the scattering directions, has been modeled as a depolarization process. The absorption/excitation of the fluorophore molecules gets revealed through the first-row elements while the emission of fluorescence has been observed through the first column elements of the fluorescence Mueller matrix. Information of the transitions between the molecular ground and excited states gets encoded into the diagonal elements following the photon selection rule. The other off-diagonal elements of the fluorescence Mueller matrix also exhibit very small nonzero values due to the anisotropic absorption and phase changes that the ground state of the fluorophore molecules imposes on the incident polarized beam while parallelly governing the emitted beam. The comparison of the current model with the earlier model has been discussed in a detailed way. The modeling of the in-between process as the depolarizing one enables us to qualify the fluorescence detected linear and circular dichroism and luminescence and very effectively overcomes the shortcomings in the earlier model.