Adiabatic following in standing-wave diffraction of atoms

We report experiments on the diffraction of atoms from a standing light wav e in the channeling regime, characterized by long interaction time and larg e potential height. The observed far-field diffraction patterns depend spec ifically on the way in which the potential is switched on and off. For fast switching, the evolution is non-adiabatic and many diffraction orders are populated. For slow switching, however, the evolution is adiabatic and the number of populated diffraction orders decreases dramatically. The experime nts are performed in two different setups employing rubidium and argon atom s, respectively. In one of the setups, we study the dependence of the diffr action pattern on the interaction time, in the other setup that on the inci dence angle.