Thermal emission of a two-dimensional semitransparent medium with discrete distributions of graded index

Abstract The backward Monte Carlo method combined with the discrete Runge-Kutta ray-tracing technique (DRKRT) is developed to simulate the thermal emission of a two-dimensional medium with discrete distributions of graded index. Refractive index and its gradient are retrieved by the moving least quare approximation. The comparison between the results predicted by the (DRKRT) and those in references shows excellent agreement, which confirms the validity of the present method. The DRKRT can be also applied to discrete distributions of graded index, given at nonuniform grids, or with data errors. For discrete distributions of nonlinear refractive index with large gradient, the accuracy of the DRKRT decreases at peaks of the apparent thermal emission, which requires finer grids.