Steven Rolston
Atomic Physics Division, NIST
Ultracold Neutral Plasmas

A laser-cooled sample of atoms (T ~ 10 microkelvin) photoionized just above threshold creates an ultracold neutral plasma. The unconfined plasma then expands into a vacuum, governed by a wide variety of effects. Evaporative cooling, adiabatic cooling, and recombination heating all act simultaneously to regulate the state of the system. A substantial fraction of the plasma recombines into Rydberg atoms. In addition, a laser-cooled sample of atoms excited to high Rydberg levels spontaneously turns into an ultracold plasma. These systems reside at the interface between single-particle atomic physics and the collective behavior of plasma physics. I will discuss recent results at NIST and elsewhere as well as theoretical efforts to understand this complex, correlated, dynamic system.