Ayman Ghabbach

Light enpolarization by disordered media under partial polarized illumination: The role of cross-scattering coefficients

We show how disordered media allow to increase the local degree of polarization (DOP) of an arbitrary (partial) polarized incident beam. The role of cross-scattering coefficients is emphasized, together with the probability density functions (PDF) of the scattering DOP. The average DOP of scattering is calculated versus the incident illumination DOP.

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.

Accurate metrology of polarization curves measured at the speckle size of visible light scattering.

An optical procedure is presented to measure at the speckle size and with high accuracy, the polarization degree of patterns scattered by disordered media. Whole mappings of polarization ratio, polarimetric phase and polarization degree are pointed out. Scattered clouds are emphasized on the Poincaré sphere, and are completed by probability density functions of the polarization degree. A special care is attributed to the accuracy of data. The set-up provides additional signatures of scattering media.

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.

Light statistics in disordered media predicted with a unique correlation parameter (Conference Presentation)

For different kinds of applications, mainly focused on probing/imaging of complex media, management of light scattering remains a challenge. Numerous studies have proven that the statistical laws followed by the intensity patterns and the polarimetric behaviour of the scattered field at the speckle scale provide a key solution to discriminate between surface and bulk scattering. It was shown for totally diffusing media that surface and bulk scattering can be seen as extreme scattering regimes. For these two regimes, exact electromagnetic calculation can be performed, but this requires a deterministic knowledge of the medium (surface profile, inhomogeneity function) under study. Furthermore these exact models are time and memory consuming, which reduces the analysis to samples with small dimensions. Within this framework statistical optics provide solutions which allow to simplify the problem. As an illustration, in previous studies our group recently proposed to use random phasors matrices to predict the statistical behaviour of surface and bulk scattering patterns in terms of intensity and polarimetric parameters. These phenomenological results were validated by comparison to both exact electromagnetic theories and experimental data, with high agreement. However in these works only the extreme scattering regimes were addressed while they involve zero or total correlation of the scattering coefficients. In this paper we show how to extend the analysis to intermediary scattering regimes, with a comparison to experiment. Furthermore we propose a simplified model involving a unique correlation parameter in the scattering matrix of a strongly disordered medium. Comparison with experiment emphasizes the validity of this model to predict the statistical behavior of the speckle patterns and their polarization properties, as well as spatial depolarization and temporal repolarization. The parameter is connected with the weight of multiple scattering and allows to consider transition between surface and bulk scattering. This statistical approach provides great help to analyze scattering media in the absence of electromagnetic theories.

Depolarizing optical multilayers

Optical coatings are known to be highly polarizing. On the other hand, they cannot reduce the degree of polarization of light. We show how to overcome this difficulty and reach spatial depolarization with significant efficiency.

Surface cross-correlation in multilayers control the polarization degree of low level scattering

Statistical optics provides a direct tool to determine correlation between interfaces of a multilayer. It is shown how this correlation controls the polarization degree of scattering. Coatings microstructure can be characterized with this procedure.