Analysis of transient radiative transfer induced by an incident short-pulsed laser in a graded-index medium with Fresnel boundaries.

Transient radiative transfer induced by a short-pulsed laser in a one-dimensional graded-index medium is investigated by the discontinuous finite element method (DFEM). The boundaries of the medium are Fresnel reflectors, and the incident pulse is considered as the combination of the collimated and the diffuse parts after its first interaction with the medium. The correctness and accuracy of the DFEM solutions for time-resolved reflectance and transmittance are first validated by comparisons with the results obtained by the Monte Carlo method, and the DFEM is then employed to investigate the transient radiative transfer in a graded-index medium with Fresnel boundaries. Effects of the refractive index distributions, the pulse width, the optical thickness, and the scattering phase functions on the transient radiative signals are examined. Several meaningful trends on the time-resolved reflectance and transmittance are observed and analyzed.