  We report on the dynamics of ultracold collisions induced by near-resonant
frequency-chirped light. A series of identical chirped pulses, separated by a
variable delay, is applied to an ultracold sample of 85Rb, and the rate of
inelastic trap-loss collisions is measured. For small detunings of the chirped
light below the atomic resonance, we observe that the rate of collisions
induced by a given pulse can be increased by the presence of an earlier pulse.
We attribute this to the enhancement of short-range collisional flux by the
long-range excitation of atom pairs to an attractive molecular potential. For
larger detunings and short delays, we find that a leading pulse can suppress
the rate of collisions caused by a following pulse. This is due to a depletion
of short-range atom pairs by the earlier pulse. Comparison of our data to
classical Monte-Carlo simulations of the collisions yields reasonable
agreement.
