Multi-grid Monte Carlo method for radiative transfer in multi-dimensional graded index media with diffuse-specular-gray boundaries

The Monte Carlo method, based on the radiative energy absorption distribution, is performed to simulate the radiative transfer in general multi-dimensional absorbing-emitting-scattering graded index media with variable refractive index and diffuse-specular-gray boundaries. A cell-based ray tracing approach is used to track the curve paths of energy particles throughout the medium. In order to accurate curved ray tracing, a multi-grid approach is used in which the domain of interest is discretized into a secondary finer grid for ray tracing, which is embedded into a primary coarser grid to simulate the radiation field. The multi-dimensional media with complex geometries are simulated by blocked-off approach. The accuracy of the present method is verified by comparing its result with benchmarks. Some examples are presented to show the performance of the present method for solving the radiative transfer in multi-dimensional graded index media with irregular geometries and diffuse-specular-gray boundaries.