ELASTIC AND INELASTIC DIFFRACTION AT GRAZING AND NORMAL INCIDENCE ON AN EVANESCENT ATOMIC MIRROR

Abstract

We will study the possibility of obtaining diffraction of atoms on a network by reflection. We will not take into account the Van der Waals potential in the following. We will describe the kinematic characteristics of the diffraction orders. We will modify the dipolar potential to represent the diffraction on a network by reflection. The dipolar potential is soft along the direction Oz and thus the diffraction at grazing incidence is eliminated in a scalar manner. The transfers of impulsion along Oz between reflected waves in the absence of modulation and the diffracted waves won’t exceed ћк where к is the decay length of the electric field. We show to a good approximation that the grating behaves as a thin phase grating which produces a spatially modulated de Broglie wave. An Ewald’s construction will help the understanding of this scalar description: we will describe the normal (quasi-effective) and the grazing incidence (very weak). In fact, the atom has many Zeeman sublevels in the fundamental state between each occur non adiabatic transitions and if we choose appropriate polarisations in the evanescent wave, we can show that the diffraction is inelastic (non scalar). We show that at grazing incidence, the diffraction is obtained only if we consider the multi-level structure of the fundamental state of the atom (stimulated Raman transitions). Effectively, as the detuning δ is large in front of the fine structure of the excited state, it is accompanied by a change in the internal atomic state of the fundamental state. Thus, it is not a scalar diffraction in the sense of the classical light optics. We will conclude by the failure of the scalar model.