  We provide a comprehensive study of ultra-cold atom diffraction by an optical
lattice. We focus on an intermediate regime between the Raman-Nath and the
Bragg regimes, the so-called quasi-Bragg regime. The experimental results are
in a good agreement with a full numerical integration of the Schr\"odinger
equation. We investigate the long pulse regime limited by a strong velocity
selection and the short pulse regime limited by non-adiabatic losses. For each
of these regimes, we estimate the multi-port features of the Bragg
interferometers. Finally, we discuss the best compromise between these two
regimes, considering the diffraction phase shift and the existence of parasitic
interferometers.
