  We present results of calculations on Bose-Einstein condensed $^{87}$Rb atoms
subjected to a moving standing-wave light-potential of the form $V_L(z,t) =
V_0(t) \cos(q z-\omega t)$. We calculate the mean-field dynamics (the order
paramter) of the condensate and determine the resulting condensate momentum in
the $z$ direction, $P_z(q,\omega,V_0,t_p)$, where $V_0$ is the peak optical
potential strength and $t_p$ is the pulse duration. Although the local density
approximation for the Bogoliubov excitation spectral distribution is a good
approximation for very low optical intensities, long pulse duration and
sufficiently large values of the wavevector $q$ of the light-potential, for
small $q$, short duration pulses, or for not-so-low intensities, the local
density perturbative description of the excitation spectrum breaks down badly,
as shown by our results.
