Physically Plausible Vectorial Metrics for Polarization Information Analysis

TL;DR

This paper introduces a physically plausible parameter set for characterizing retarders in polarization analysis, avoiding structural assumptions and improving accuracy in biomedical and material applications.

Contribution

It proposes a new parameter set for retarder characterization that better reflects actual structures without relying on layered models.

Findings

Validated on liquid crystalline samples

Provides a comprehensive optical response characterization

Enhances applications in biomedical imaging and material 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 modelled as a circular retarder followed by a linear retarder when using this approach. 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 a physically plausible parameter set that includes the axis orientation angle $\phi$, the degree of ellipticity $\chi$, and the elliptical retardance $\rho$. By working with this set of parameters, an overall characterization of a 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 physically plausible parameter set adopted provides a useful tool for a broader range of applications in both biomedical imaging and optical material analysis.