Semi-infinite-geometry boundary problem for light migration in highly scattering media: a frequency-domain study in the diffusion approximation

Received December 13, 1993; revised manuscript received May 5, 1994 We have studied light migration in highly scattering media theoretically and experimentally, using the diffusion approximation in a semi-infinite-geometry boundary condition. Both the light source and the detector were located on the surface of a semi-infinite medium. Working with frequency-domain spectroscopy, we approached the problem in three areas: (1) we derived theoretical expressions for the measured quantities in frequency-domain spectroscopy by applying appropriate boundary conditions to the diffusion equation; (2) we experimentally verified the theoretical expressions by performing measurements on a macroscopically homogeneous medium in quasi-semi-infinite-geometry conditions; (3) we applied Monte Carlo methods to simulate the semi-infinite-geometry boundary problem. The experimental results and the confirming Monte Carlo simulation show that the diffusion approximation, under the appropriate boundary conditions, accurately estimates the optical parameters of the medium.