  The efficiency of an atomic interferometer in proximity of a surface is
discussed. We first study which is the best choice of frequency for a pulse
acting on internal atomic transitions in the same well. Then considering the
modification of atomic energy levels in vicinity of the surface, we propose the
application of two simultaneous Raman lasers and numerically study the
associated interference fringes. We show that the efficiency of the
interferometric scheme is limited by the existence of a residual phase
depending on the atomic path. We propose a symmetric scheme in order to avoid
these contributions. We finally show that the suggested modifications make the
contrast of the interference fringes close to 1 in any configuration, both
close and far from the surface and with one or more initially populated wells.
