Curious behavior of optically trapped neutral atoms

We have studied the behavior of clouds of neutral atoms contained in a spontaneous force optical trap. Because of the low temperatures of the atoms (<1 mK) we have observed a variety of new phenomena which involve both short and long range interactions between the atoms. The short range interactions are manifested in two body collisions which are notable because of the very long collision times. This time scale causes the dynamics to be profoundly affected by absorption and spontaneous emission during the collision. An interesting assortment of collective behaviors are observed when the trapped atom cloud contains more than 105 atoms. These include the expansion of the cloud as the number is increased and dramatic changes in the distribution of the atoms at higher numbers. We can explain much of the collective behavior using a simple model that includes a 1/r2 force between the atoms arising from the multiple scattering of photons. Finally, we discuss the optical trapping of atoms directly from a low pressure vapor in a small glass cell. We have used these optically trapped atoms to load a magnetostatic trap in the same cell. This provided a high density sample of atoms with a temperature of less than 2 μK