Laser speckle contrast vs. depolarization: a solid skin phantom study

Laser light propagated in semi-transparent turbid media such as biological tissue loses its coherence and polarization. Speckle contrast can be considered as a metric of light coherence. Recently we demonstrated that polychromatic speckle contrast and degree of polarization are useful criteria for skin lesion differentiation. To gain a better understanding of this complex process, we conducted an experiment to measure the speckle contrast and the average degree of polarization of solid skin phantoms with controllable roughness and bulk optical parameters of the order of human skin. The data validated that bulk scattering along with roughness introduce speckle contrast and DOLP reduction. Also we observed that speckle contrast and the average degree of polarization were related to the bulk scattering coefficient. The speckle contrast vs. degree of linear polarization dependence reveals a near linear relationship with the slope varying with the scattering coefficient of the material. The significant difference between slopes for two phantoms with slightly dissimilar optical properties could suggest that this pair of measurements (speckle contrast vs. degree of linear polarization) is highly sensitive to the tissue type and can be potentially used as a parameter for material differentiation.