BRAGG SCATTERING OF SLOW ATOMS FROM A STANDING LIGHT-WAVE

Slow atoms from a magneto-optical trap are used to study diffraction f rom a near-resonant standing-wave light field. Long interaction times make it possible to observe unidirectional Bragg scattering. In partic ular, the Pendellosung interference effect between two resonant moment um states is demonstrated for first- and second-order diffraction. The oscillation frequency of second-order scattering shows a transition f rom a four-photon-type process at low light intensity to a two-photon- type process at higher intensity. The data are in quantitative agreeme nt with a theoretical description which takes into account lowest-ener gy momentum states.