Transient radiative transfer in a complex refracting medium by a modified Monte Carlo simulation

A modified Monte Carlo (MMC) method applied with time shift and superposition principle is developed for solving transient radiative transfer in one-dimensional scattering media with arbitrary distributions of refractive index exposed to a collimated short pulse-laser irradiation at one of its boundaries. We consider a multilayer medium and a graded index medium. The accuracy and computational efficiency of the MMC algorithm are examined firstly. Our results are compared with those obtained by the reverse Monte Carlo method (RMC), the modified discrete ordinates method (MDOM) and the lattice Boltzmann method (LBM), and the excellent agreements are achieved. With the time shift and superposition principle, the MMC method can greatly improve the computational efficiency. We have a parametric investigation on the transient radiative transfer in the three-layer systems and graded-index media, illustrating the effects of refractive index distribution, optical thickness, interface/surface reflection mode, scattering phase function and scattering albedo on the time-resolved signals of reflectance and transmittance. Results show that the reflection mode has an important influence on the transient radiative transfer; the specular reflection at interfaces/boundaries can enhance the effects of forward scattering, while the diffuse reflection can enhance the effects of backward scattering.