Creation of an Ultracold Neutral Plasma

We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as $2\times {10}^9{\mathrm{cm}}^{-3\mathrm{}}$, and the temperatures of electrons and ions are as low as 100 mK and $10\mu \mathrm{K}$, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that both electrons and ions are strongly coupled.