Ultracold neutral plasmas: recent experiments and new prospects

Photoionizing laser-cooled atoms produces ultracold neutral plasmas with initial temperatures of 1-1000 K and densities as high as 10(10) cm(-3). Applied radio frequency fields can excite plasma oscillations that are used to monitor the expansion of the unconfined plasma. Significant three-body recombination of electrons and ions into Rydberg atoms takes place during the plasma expansion. Previous experiments have been done with xenon, but a new experiment is planned with laser-cooled strontium. The strontium ion has an optically allowed transition at a convenient blue wavelength. This will allow direct imaging of the plasma through fluorescence or absorption, and may enable laser cooling and trapping of the plasma.