Abstract: Optical techniques represent a valuable tool for analysis of turbid media. Recent development has emphasized dynamic measurements where either ultrashort laser pulses or high frequency amplitude modulated laser light are launched into the medium. The properties of the transmitted light range from quasi- coherent in media with limited scattering to the almost randomized incoherent behavior in strongly turbid media. The present discussion considers the influence of a boundary between a heavily scattering medium with an almost isotropic diffuse light distribution and a non-scattering medium. This case can be approximated in terms of well established solutions of the diffusion equation. It is further demonstrated that the somewhat composite mathematical expressions can be interpreted in a very simple, intuitive manner. This type of approximation is, of course, of limited validity in the surface layer itself. However, the simplicity of this approximation might make it a valuable tool for several applications. !13
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