  We present an elegant application of matterwave interferometry to the
velocimetry of cold atoms whereby, in analogy to Fourier transform
spectroscopy, the 1-D velocity distribution is manifest in the frequency domain
of the interferometer output. By using stimulated Raman transitions between
hyperfine ground states to perform a three-pulse interferometer sequence, we
have measured the velocity distributions of clouds of freely-expanding
$^{85}$Rb atoms with temperatures of 33 $\mu$K and 17 $\mu$K. Quadrature
measurement of the interferometer output as a function of the temporal
asymmetry yields velocity distributions with excellent fidelity. Our technique,
which is particularly suited to ultracold samples, compares favourably with
conventional Doppler and time-of-flight techniques, and reveals artefacts in
standard Raman Doppler methods. The technique is related to, and provides a
conceptual foundation of, interferometric matterwave accelerometry, gravimetry
and rotation sensing.
