Diffraction of atoms from a standing light wave

Abstract

This paper presents experiments concerning momentum transfer to atoms by a standing light wave in the absence of spontaneous decay. This momentum transfer, which occurs in discrete units of 2 ħ k along the k -vector of the standing light wave, can be viewed as absorption/stimulated emission of photon pairs from the counterpropagating traveling waves which make up the standing light wave. In a dual sense, this phenomenon can also be viewed as diffraction of an atomic de Broglie wave from the periodic intensity grating of the standing light wave. In addition, we address how the inherent Heisenberg uncertainty between the focussed waist of the standing light wave and the angular spread of the k -vectors of photons traveling through this waist affects momentum transfer to the atoms by the light. For large widths of the standing light wave, the reduction of the uncertainty in the direction of the photons results in resonances for the momentum transfer only for discrete values of atomic momentum along the k -vector of the standing light wave which satisfy the Bragg condition. We present experimental data which display the Pendellösung effect for Bragg scattering of atomic de Broglie waves from a standing light wave. Finally, we discuss the possibility of exploiting these phenomena to build an atomic interferometer, one that interferes atomic de Broglie waves.