Temperature oscillation in an ultracold plasma as a function of time after photoionization. (Left) Image of electron distribution of a xenon plasma using projection imaging onto a charged particle detector. (Center) Image of a strontium plasma taken by measuring the absorption of resonant laser light. (Right) The kinetic energy of a strontium plasma (where the ions are in Gaussian cloud of size σ) shortly after formation for an inner region (radius ρ<0.9σ) and outer region (radius ρ>1.49σ) of the plasma. The oscillations visible are a sign of correlations and the strong coupling regime.