Modeling of ultrashort light pulse propagation in light scattering media

Light pulses have found increasing use in medicine and biology. Biological tissues, however, scatter light very strongly, and the modeling of light pulse propagation in biological tissues has not been established because of scattering. We compare the results of three modeling methods, the photon diffusion approximation, the diffusive wave approximation, and the two-flux method with those of the discrete ordinate method which provides the exact solution of the transient equation of radiative transfer for the case of 1 picosecond pulse incidence on scattering and absorbing slab or semi-infinite media simulating biological tissues. The early behavior of the light pulses predicted by the photon diffusion approximation is quite different from that by the diffusive wave approximation. In the later period both the photon diffusion and diffusive wave approximations are able to give reasonable results, but the two-flux method is not. Because of much shorter computation time, the diffusive wave approximation is advantageous to the photon diffusion approximation.