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The backscattering of polarised light from turbid media - An analysis of the azimuthal intensity variations and its implications for the position of the source of diffusing radiation

Venkatesh Gopal·Hema Ramachandran·A. K. Sood
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Abstract

We study the azimuthal variation in the backscattered intensity that is seen when polarised light is scattered by a turbid medium. We present experimental observations of these intensity variations in colloidal suspensions over a wide range of optical densities. For a medium composed of spherical scatterers, we have developed using Mie scattering theory and Monte Carlo simulations of photon transport, a model which calculates the constant intensity contours of the backscattered intensity. Comparisons of calculated and experimentally obtained contours show very good agreement. To our knowledge, this is the first model to provide a quantitative comparison with experimental data. Close to the exact backscattering direction, where we have made our intensity measuements, we show that the patterns are formed by what we have called `reflected snake photons'. These are photons that have been backscattered once and have maintained their direction of propagation thereafter until they exit the medium. We also find that the reflected snake photons originate within a depth of about $4l^{*}$ from the point of entry of the incident beam, where $l^{*}$ is the photon transport mean free path. Further, in a novel approach, we have used these patterns as a probe of the assumptions underlying the diffusion approximation and present new results on the position of the apparent source of diffusing radiation within the medium. Possible applications are also discussed.

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Venkatesh Gopal, Hema Ramachandran, A. K. Sood. 1999-06-15. The backscattering of polarised light from turbid media - An analysis of the azimuthal intensity variations and its implications for the position of the source of diffusing radiation. https://arxiv.org/abs/cond-mat/9906227

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