Elliptical vectorial metrics for physically plausible polarization information analysis

Abstract

The Mueller matrix polar decomposition method decomposes a Mueller matrix into a diattenuator, a retarder, and a depolarizer. Among these elements, the retarder, which plays a key role in medical and material characterization, is usually modelled as a circular retarder followed by a linear retarder. However, this model may not accurately reflect the actual structure of the retarder in certain cases as many practical retarders do not have a layered structure or consist of multiple (unknown) layers. Misinterpretation, therefore, may occur when the actual structure differs from the model. Here, we circumvent this limitation by proposing to use an elliptical retarder parameter set that includes the axis orientation angle φ, the degree of ellipticity χ, and the elliptical retardance ρ. By working with this set of parameters, an overall characterization of any retarder is provided, encompassing its full optical response without making any assumptions about the structure of the material. In this study, experiments were carried out on liquid crystalline samples to validate the feasibility of our approach, demonstrating that the elliptical retarder parameter set adopted provides a useful tool for a broader range of applications in optical material analysis.