  We theoretically consider the effect of the atomic source's momentum width on
the efficiency of Bragg mirrors and beamsplitters and, more generally, on the
phase sensitivity of Bragg pulse atom interferometers. By numerical
optimization, we show that an atomic cloud's momentum width places a
fundamental upper bound on the maximum transfer efficiency of a Bragg mirror
pulse, and furthermore limits the phase sensitivity of a Bragg pulse atom
interferometer. We quantify these momentum width effects, and precisely compute
how mirror efficiencies and interferometer phase sensitivities vary as
functions of Bragg order and source type. Our results and methodology allow for
an efficient optimization of Bragg pulses and the comparison of different
atomic sources, and will help in the design of large momentum transfer Bragg
mirrors and beamsplitters for use in atom-based inertial sensors.
