Enpolarization and depolarization of light scattered from chromatic complex media

Definition of a second-order degree of polarization in terms of the complex degree of coherence

The classical theory of random electric fields and polarization formalism has been formulated considering the Stokes parameters' auto-correlations. However, in this work, the need to consider the Stokes parameters' cross-correlations to obtain a complete description of the polarization dynamics of a light source is explained. We propose a general expression for the Stokes parameters' degree of correlation using both auto-correlations and cross-correlations, which we derive from the application of Kent's distribution in the statistical study of Stokes parameter dynamics on Poincaré's sphere. Additionally, from the proposed degree of correlation, we obtain a new expression for the degree of polarization (DOP) in terms of the complex degree of coherence, which is a generalization of the well-known Wolf's DOP. The new DOP is tested using a depolarization experiment in which partially coherent light sources propagate through a liquid crystal variable retarder. The experimental results show that our generalization for the DOP improves the theoretical description of a new depolarization phenomenon that Wolf's DOP cannot describe.

Unraveling the physical information of depolarizers

The link between depolarization measures and physical nature and structure of material media inducing depolarization is nowadays an open question. This article shows how the joint use of two complementary sets of depolarizing metrics, namely the Indices of polarimetric purity and the Components of purity, are sufficient to completely describe the integral depolarizing properties of a sample. Based on a collection of illustrative and representative polarimetric configurations, a clear and meaningful physical interpretation of such metrics is provided, thus extending the current tools and comprehension for the study and analysis of the depolarizing properties of material media. This study could be of interest to those users dealing with depolarization or depolarizing samples.

Combining light polarization and speckle measurements with multivariate analysis to predict bulk optical properties of turbid media

This study aims to investigate the combination of speckle pattern analysis, polarization parameters, and chemometric tools to predict the optical absorption and scattering properties of materials. For this purpose, an optical setup based on light polarization and speckle measurements was developed, and turbid samples were measured at 405 and 660 nm. First, a backscattered polarized speckle acquisition was performed on a set of 41 samples with various scattering (${\mu}_s$μ_s) and absorbing (${{\mu}_a}$μ_a) coefficients. Then, several parameters were computed from the polarized speckle images, and prediction models were built using stepwise multiple linear regression. For scattering media, ${{\mu}_s}$μ_s was predicted with ${R^{2} = 0.9}$R²=0.9 using two parameters. In the case of scattering and absorbing media, prediction results using two parameters were ${R^{2} = 0.62}$R²=0.62 for ${{\mu}_s}$μ_s and ${R^{2} = 0.8}$R²=0.8 for ${{\mu}_a}$μ_a. The overall results obtained in this research showed that the combination of speckle pattern analysis, polarization parameters, and chemometric tools to predict the optical bulk properties of materials show interesting promise.

On the enpolarization/depolarization effects of deterministic devices

A Poincaré sphere geometric approach to the enpolarization/depolarization effects of dichroic devices/media is presented. The degree of polarization (DoP) of the emergent light is expressed as a function of two parameters: the DoP of the incident light and the dichroic strength of the device. The polar plots of this dependence give an intuitive grasp on how the alternation of the two effects depends on the competition between these parameters. The same approach can be transposed in an adapted terminology in various fields of physics, in all the problems whose underpinning mathematics is that of Lorentz transformation.

Transmission versus reflectance spectroscopy for quantitation

The objective of this work was to compare the accuracy of analyte concentration estimation when using transmission versus diffuse reflectance spectroscopy of a scattering medium. Monte Carlo ray tracing of light through the medium was used in conjunction with pure component absorption spectra and Beer-Lambert absorption along each ray's pathlength to generate matched sets of pseudoabsorbance spectra, containing water and six analytes present in skin. PLS regression models revealed an improvement in accuracy when using transmission compared to reflectance for a range of medium thicknesses and instrument noise levels. An analytical expression revealed the source of the accuracy degradation with reflectance was due both to the reduced collection efficiency for a fixed instrument etendue and to the broad pathlength distribution that detected light travels in the medium before exiting from the incident side.

Evolution of circular and linear polarization in scattering environments

This work quantifies the polarization persistence and memory of circularly polarized light in forward-scattering and isotropic (Rayleigh regime) environments; and for the first time, details the evolution of both circularly and linearly polarized states through scattering environments. Circularly polarized light persists through a larger number of scattering events longer than linearly polarized light for all forward-scattering environments; but not for scattering in the Rayleigh regime. Circular polarization's increased persistence occurs for both forward and backscattered light. The simulated environments model polystyrene microspheres in water with particle diameters of 0.1 μm, 2.0 μm, and 3.0 μm. The evolution of the polarization states as they scatter throughout the various environments are illustrated on the Poincaré sphere after one, two, and ten scattering events.

Speckle intensity statistics for chromatic scattering media under partially polarized illumination

Intensity contrast in a fully developed speckle pattern resulting from the elastic scattering of a partially polarized light from a strongly scattering medium is theoretically and numerically studied. Simple expressions are derived when the illumination bandwidth is much smaller or larger than the chromatic length of the scattering medium.

Spatial depolarization of light from the bulks: electromagnetic prediction

The spatial depolarization of light emitted by heterogeneous bulks is predicted with exact electromagnetic theories. The sample microstructure and geometry is connected with partial polarization.

Polarization analysis of speckle field below its transverse correlation width : application to surface and bulk scattering

An experimental method for accurate polarimetric characterization of speckle field below its transverse correlation width is proposed. Using a polarimetric analyzer, the speckle field under investigation is probed by a set of polarimetric projections describing the full Poincaré sphere surface. Spatial polarimetric variations of the speckle field are thus observed with an accuracy of 1% for each Stokes parameter. Moreover, all the experimental data can be guaranteed by a validity criterion. Using white paper sheet and rough metal samples, the method exhibits strong potential to analyze and differentiate speckle fields generated by bulk and surface scattering.

Depolarization and enpolarization dop histograms measured for surface and bulk speckle patterns

dop histograms are measured in the off-specular far field speckle of disordered media under polarized and unpolarized illumination. Three surface samples with increasing roughnesses, and three bulk samples with different absorption levels, are investigated. Results show that both rough surfaces and absorbing bulks hold the incident polarization, while transparent bulks allow to depolarize or to enpolarize the incident light. Hence we provide a first experimental evidence of such effects.