  We apply optical pumping to prepare the lithium beam of our atom
interferometer in a single hyperfine-Zeeman sublevel: we use two components of
the D1-line for pumping the 7Li atoms in a dark state F,mF=+2 (or -2) sublevel.
The optical pumping efficiency has been characterized by two techniques:
state-selective laser atom deflection or magnetic dephasing of the atom
interferometer signals. The first technique has not achieved a high
sensitivity, because of a limited signal to noise ratio, but magnetic dephasing
signals have shown that about 95% of the population has been transferred in the
aimed sublevel, with similar results for three mean velocities of the atomic
beam covering the range 744-1520m/s.
