Killian, TC, Chen YC, Gupta P, Laha S, Martinez YN, Mickelson PG, Nagel SB, Saenz AD, Simien CE.
2005.
Ultracold neutral plasmas, May. Plasma Physics and Controlled Fusion. 47:A297-A306.
AbstractUltracold neutral plasmas are formed by photo-ionizing laser-cooled atoms near the ionization threshold. Through the application of atomic physics techniques and diagnostics, these experiments stretch the boundaries of traditional neutral plasma physics. The electron temperature in these plasmas ranges from 1 to 1000 K and the ion temperature is around 1 K. The density can approach 10(11) cm(-3). Fundamental interest stems from the possibility of creating strongly coupled plasmas, but recombination, collective modes, and thermalization in these systems have also been studied. Optical absorption images of a strontium plasma, using the Sr+ S-2(1/2) -> P-2(1/2) transition at 422 mn, depict the density profile of the plasma, and probe kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum measures the ion velocity distribution, which gives an accurate measure of the ion dynamics in the first microsecond after photo-ionization.
Simien, CE, Chen YC, Gupta P, Laha S, Martinez YN, Mickelson PG, Nagel SB, Killian TC.
2004.
Using absorption imaging to study ion dynamics in an ultracold neutral plasma, Apr. Physical Review Letters. 92:4., Number 14
AbstractWe report optical absorption imaging of ultracold neutral strontium plasmas. The ion absorption spectrum determined from the images is Doppler broadened and thus provides a quantitative measure of the ion kinetic energy. For the particular plasma conditions studied, ions heat rapidly as they equilibrate during the first 250 ns after plasma formation. Equilibration leaves ions on the border between the weakly coupled gaseous and strongly coupled liquid states. On a longer time scale of microseconds, pressure exerted by the trapped electron gas accelerates the ions radially.