Absorption distribution of an optical beam focused into a turbid medium

The focusing of light into a turbid medium was studied with Monte Carlo sim ulations. Focusing was found to have a significant effect on the absorption distribution in turbid media when the depth of the focal point (the distan ce between the focal point and the surface of the turbid media) was less th an or comparable with the transport mean free path. Focusing could signific antly increase the peak absorption and narrow the absorption distribution. As the depth of the focal point increased, the peak absorption decreased, a nd the depth of peak absorption increased initially but quickly reached a p lateau that was less than the transport mean free path. A refractive-index- mismatched boundary between the ambient medium and the turbid medium deteri orated the focusing effect, increased the absorption near the boundary, low ered the peak absorption, and broadened the absorption distribution. (C) 19 99 Optical Society of America.