Depolarization of light in biological tissues

Recently in phototherapy the use of diodes and broadband light devices instead of lasers was suggested for economical and practical reasons. It has been argued that lasers are not superior to LEDs since they lose their coherence and polarization once they penetrate into biological tissues. However, the polarization point has never been experimentally proven. In this work, to the best of our knowledge, we have for the first time experimentally validated the conditions that affect the polarization state of light when laser illumination propagates through a biological tissue with and without flow. In our experiments we measured the polarization of light passing through phantoms as well as through uncooked turkey meat. The measurements were performed for varied integration time, thickness and flow rates. It was experimentally validated that the tissue thickness hardly influences the polarization in comparison to flow for a reduced scattering coefficient of 0.8 mm(-1) while there is no flow. Furthermore, when the flow is perpendicular to the polarization plane its velocity highly affects the polarization. However, when the flow is parallel to the polarization plane there is almost no change in the propagating light's polarization state. Thus, one outcome of this work is that since the biological tissue is not static and contains many blood vessels and capillaries, the polarization of the laser may be lost when light penetrates the tissue. (C) 2012 Elsevier Ltd. All rights reserved.