  We measure the response of an elongated Bose-Einstein condensate to a
two-photon Bragg pulse. If the duration of the pulse is long, the total
momentum transferred to the condensate exhibits a nontrivial behavior which
reflects the structure of the underlying Bogoliubov spectrum. It is thus
possible to perform a spectroscopic analysis in which axial phonons with
different number of radial nodes are resolved. The local density approximation
is shown to fail in this regime, while the observed data agrees well with the
results of simulations based on the numerical solution of the Gross-Pitaevskii
equation.
