ENERGY VELOCITY OF DIFFUSING WAVES IN STRONGLY SCATTERING MEDIA

Measurements of the diffusive transport of multiply scattered ultrason ic waves show that the energy velocity is very similar in magnitude an d frequency dependence to the group velocity. Our data are accurately described using a theoretical model that accounts for the renormalizat ion of scattering by the coupling between neighboring scatterers, quan titatively predicting the scattering delay that causes the strong freq uency dependence of these velocities seen in our experiments. This giv es a unified physical picture of the velocities of energy transport by both diffusive and ballistic waves. [S0031-9007(97)04300-7].