Adiabatic following in standing-wave diffraction of atoms

We report experiments on the diffraction of atoms from a standing light wave in the channeling regime, characterized by long interaction time and large potential height. The observed far-field diffraction patterns depend specifically 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 experiments are performed in two different setups employing rubidium and argon atoms, respectively. In one of the setups, we study the dependence of the diffraction pattern on the interaction time, in the other setup that on the incidence angle. Received: 30 November 1998 / Revised version: 5 July 1999 / Published online: 8 September 1999