Absorption Imaging and Spectroscopy of Ultracold Neutral Plasmas
  Absorption imaging and spectroscopy can probe the dynamics of an ultracold neutral plasma during the first few microseconds after its creation. Quantitative analysis of the data, however, is complicated by the inhomogeneous density distribution, expansion of the plasma, and possible lack of global thermal equilibrium for the ions. In this article we describe methods for addressing these issues. Using simple assumptions about the underlying temperature distribution and ion motion, the Doppler-broadened absorption spectrum obtained from plasma images can be related to the average temperature in the plasma. 
T. C. Killian, Y. C. Chen, P. Gupta, S. Laha, Y. N. Martinez, P. G.   Mickelson, S. B. Nagel, A. D. Saenz, and C. E. Simien