Atomic motion in longitudinally modulated light crystals

We study the dynamics of atomic waves in longitudinally modulated light cry stals using an effective complex potential with time (space) dependent detu ning. In the weak coupling regime we predict a sharp asymmetry of the scatt ering probability near the Bragg angle. In the strong coupling case we intr oduce the concept of a light crystal with "complex kick." We have found tha t the initially blue detuned crystal is much more transparent for atomic wa ves. Moreover, the probability distribution of the outgoing wave shows carp etlike interference structure.