Dynamics of photoinduced collisions of cold atoms probed with picosecond laser pulses

Pump-probe experiments are performed in which cold colliding Na atoms are photoassociated to form Na-2. molecules, and subsequently ionized. The experiments are performed in a regime where the pulsed photoassociation to an intermediate potential takes place at long range, and to several electronic, vibrational, and rotational states. A probe pulse then produces an ionization signal by further exciting these molecules to autoionizing doubly excited states. The time dependence of the ion signal shows a dramatic flux-enhancement effect on a nanosecond time scale due to the motion on the intermediate potentials. This time dependence can be viewed as monitoring the inward motion and dephasing of a population wave packet formed at long range.