Location of the effective diffusing-photon source in a strongly scattering medium

摘要

When a narrow laser beam illuminates a strongly scattering medium, the effective pointlike source of diffusing photons appears inside the medium. By the method worked out, which is based on measurements of the diffusive intensity of light emerging from a turbid spherical sample, the depth of this source site (the penetration depth) is determined relatively to the sample diameter, which is known accurately. By using this method of locating the effective source, we have discovered that its position inside the medium is unexpectedly deep. We obtained the penetration depth Delta(0) = 4.6l* +/- 0.7l* instead of one transport mean free path, where l* is the value of Delta(0) in the standard diffusion theory. Information about this source dipping is useful in diffusing-photon correlation spectroscopy because of its influence on the geometric factor calculated from the diffusion equation. (C) 1997 Optical Society of America.