  We propose a mechanism for a velocity-selective device, which exploits the
fundamental phenomenon of dynamical localization. It would allow packets of
cold atoms travelling through a pulsed optical lattice in one direction to pass
undisturbed, while dispersing atoms travelling in the opposite direction. This
mechanism is based on a chaotic diffusion process, with a momentum-dependent
diffusion coefficient. We analyse this classical effect, and we show that it is
enhanced by dynamical localization.
