Motion of intensity maxima in averaged speckle patterns of transmitted radiation.

We show intensity maxima in speckle patterns averaged over a frequency interval diffuse as the frequency is scanned with a diffusion coefficient that decreases linearly with the width of the frequency interval for moderate intervals. This makes it possible to find the diffusion coefficient even with data averaged over a frequency window. These results apply as well to speckle patterns averaged over time in systems with internal motion and so provide a means for characterizing dynamic systems.