Noise sensitivity of an atomic velocity sensor

We use Bloch oscillations to accelerate coherentlyrubidium atoms. The variation of the velocity induced by thisacceleration is an integer number times the recoil velocity due tothe absorption of one photon. The measurement of the velocityvariation is achieved using two velocity selective Raman -pulses: the first pulse transfers atoms from the hyperfine state5S1/2, to 5S1/2, into a narrow velocity class. After theacceleration of this selected atomic slice, we apply the secondRaman pulse to bring the resonant atoms back to the initial state5S1/2, . The populations in (F=1and F=2) are measured separately by using a one-dimensionaltime-of-flight technique. To plot the final velocity distributionwe repeat this procedure by scanning the Raman beam frequency ofthe second pulse. This two -pulses system constitutes then avelocity sensor. Any noise in the relative phase shift of theRaman beams induces an error in the measured velocity. In this paperwe present a theoretical and an experimental analysis of thisvelocity sensor, which take into account the phase fluctuationsduring the Raman pulses.