  We study photon echo generation in disordered media with the help of multiple
scattering theory based on diagrammatic approach and numerical simulations. We
show that a strong correlation exists between the driving fields at the origin
of the echo and the echo beam. Opening the way to a better understanding of
non-linear wave propagation in complex materials, this work supports recent
experimental results with applications to the measurement of the optical dipole
lifetime $T_2$ in powders.
