We have developed a new diagnostic tool for the study
of Zeeman-compensated slowing of an alkali atomic beam.
Our time-of-flight technique measures the longitudinal veloc-
ity distribution of the slowed atoms with a resolution below
the Doppler limit of 30 cm/s. Furthermore, it can map the
position and velocity distribution of atoms in either ground
hyperfine level inside the solenoid without any devices inside
the solenoid. The technique reveals the optical pumping ef-
fects, and shows in detail how the slowing within the solenoid
proceeds. We find that most atoms in the chosen hyperfine
state are decelerated in the slowing process. The width of the
velocity distribution is mainly determined by inhomogeneities
in the slowing laser beam, and after expanding the laser beam,
the width is reduced to 2.5 m/s, corresponding to 3.2 mK. Fi-
nally, we discuss and show a method to produce a beam with
two-velocity components for the study of head-tail low energy
collisions.