Numerical simulations of scattering speckle from phase ordering systems

The scattering of coherent X-rays from dynamically evolving systems is currently becoming experimentally feasible. The scattered beam produces a pattern of bright and dark speckles, which fluctuate almost independently in time and can be used to study the dynamics of the system. Here we report large-scale computer simulations of the speckle dynamics for a phase-ordering system, using a two-dimensional model quenched through an order-disorder transition into the two-phase regime. The intensity at each wave vector It is found to be an exponentially distributed random variable. The scaling hypothesis is extended to the two-time correlation function of the scattering intensity at a given wave vector, Corr(k; t(1),t(2)). The characteristic decay time difference for the correlation function, \t(1) - t(2)\(c), is found to scale as k\t(1) + t(2)\(1/2).