Time resolved reflectance of an optical pulse from scattering bodies with nonscattering regions utilizing the finite difference time domain analysis

The finite difference time domain (FDTD) analysis has been successfully formulated for predicting time resolved reflectance of an optical pulse from scattering bodies with nonscattering (clear) regions. The nondiffusive light propagation across a clear region has been calculated based on the invariance of the light intensity along the ray in free space. The additional equivalent source functions generated by the nondiffusive light entering the scattering region have been introduced into the diffusion equations and the FDTD analysis has been formulated. Time resolved reflectance of the three-layered slab containing a clear layer was calculated based on the formulation. It has been become clear that received light intensity and mean time of flight estimated from the reflectance agree with previously reported experimental data quite well. It has also been found that the absorption loss of the scattering region beyond the clear layer is estimated from the time resolved reflectance.