Characterization of anisotropy of the porous anodic alumina by the Mueller matrix imaging method.

Porous anodic alumina (PAA) is a photonic crystal with a hexagonal porous structure. To learn more about the effects brought by pores on the anisotropy of the PAA, we use the orientation sensitive Mueller matrix imaging (MMI) method to study it. We fabricated the PAA samples with uniform pores and two different pore diameters. By the MMI experiments with these samples, we found that the birefringence is the major anisotropy of the PAA and that there are many small areas with different orientations that formed spontaneously in the process of production on the surface of the PAA. By the MMI experiments at different orientations of the sample with two different pore diameters, we found that the pores affect the birefringence of the sample and the effect increases with the increased inclination of the sample. To further analyze the PAA, we present a symmetrical rotation measurement method according to the Mueller matrix of the retarder. With this method, we can calculate the average refractive index (RI) of birefringence and the orientation of the optical axis of uniaxial crystal. The results also show the effect of the pores on the anisotropy of PAA.

Separating azimuthal orientation dependence in polarization measurements of anisotropic media.

Polarization imaging and Mueller polarimetry provide powerful tools for probing the microstructure of complex anisotropic media, which is a core task in material science, biomedical diagnosis and many research fields. However, Mueller matrix elements and many polarization parameters are sensitive to the spatial orientation of the sample and experimental configurations, hindering the effectiveness for distinguishing different sources of anisotropies. In this paper, we propose a set of rotation invariant parameters and corresponding orientation parameters, which are explicit functions of the Mueller matrix elements. They are valid under the condition that the illumination and detection directions are collinear with the rotation axis of the sample. More detailed examinations show that these parameters have potential applications for fast analyzing different anisotropy contributions in the media, such as birefringence, dichroism, and their coexistence. The conclusions are validated with Monte Carlo simulations and the experimental results of transparent tape samples.

Physically Realizable Space for the Purity-Depolarization Plane for Polarized Light Scattering Media.

We propose a physically realizable space for the polarized light scattering measurement using the Stokes-Mueller formalism by a purity-index-depolarization-index (PI-P_{Δ}) plane. The parameter PI is defined from indices of polarimetric purity (IPP), which exhibits the overall magnitude of the polarimetric randomness of a medium, while the depolarization index (P_{Δ}) delineates a proper global degree of polarimetric purity and may also refer to the average measure of depolarization power of the scattering medium. Subregions and curves connecting the edge points in the plane are obtained by imposing certain constraints on the IPP; consequently any point on the subregion indicates the information related to a decomposition of the Mueller matrix into its components as a convex sum. From the same set of constraints, complete information about the depolarization index versus the entropy [S(M)-P_{Δ}] diagram is recovered. This work provides a simple geometric representation and a deeper perceptivity of the light scattering media comprising depolarization.

Monitoring microstructural variations of fresh skeletal muscle tissues by Mueller matrix imaging.

Recently many attempts have been made for extracting the structural information of myofibrils as indicators for diseases of skeletal muscle. In this paper we adopt wide-field illumination and take the backscattering Mueller matrix images of bovine skeletal muscle tissues during the 24-hour experimental time after the animal's death. The 2D images of Mueller matrix elements and their frequency distribution histograms (FDHs) reveal rich qualitative information on the changes in the microstructures of the skeletal muscle. The temporal variations of the sample are quantitatively analyzed using two Mueller matrix transformation (MMT) parameters. The characteristic features of the temporal plots are attributed to the rigor mortis and proteolysis processes. For a deeper insight on the relationship between the features of the MMT parameters and the microstructures during the rigor mortis and proteolysis processes, Monte Carlo (MC) simulations are carried out based on sphere-cylinder birefringence model (SCBM). The good agreement between the experimental and MC simulated results show that the FDHs and MMT parameters can describe more clearly the characteristic microstructural features of skeletal muscle tissues. The techniques are useful for the characterization of physiological status of tissues, or quantitative assessment of meat qualities in food industry.