A diffusion model for light scattering in ejecta

We derive a diffusion equation for light scattering from ejecta produced by extreme shocks on metallic samples. This model is easier to handle than a more conventional model based on the Radiative Transfer Equation (RTE), and is a relevant tool to analyze spectrograms obtained from Photon Doppler Velocimetry (PDV) measurements in the deep multiple scattering regime. We also determine the limits of validity of the diffusive model compared to the RTE, based on a detailed analysis of various ejecta properties in configurations with increasing complexity.