  The sensitivity of an inertial sensor based on an atomic interfermometer is
proportional to the velocity separation of atoms in the two arms of the
interferometer. In this paper we describe how Bloch oscillations can be used to
increase this separation and to create a large momentum transfer (LMT)
beamsplitter. We experimentally demonstrate a separation of 10 recoil
velocities. Light shifts during the acceleration introduce phase fluctuations
which can reduce the contrast of the interferometer. We precisely calculate
this effect and demonstrate that it can be significantly reduced by using a
suitable combination of LMT pulses. We finally show that this method seems to
be very promising to realize LMT beamsplitter with several 10s of recoil and a
very good efficiency.
