  We report new measurements and simulations of laser-induced fluorescence in
ultracold neutral plasmas. We focus on the earliest times, when the plasma
equilibrium is evolving and before the plasma expands. In the simulation, the
ions interact via the Yukawa potential in a small cell with wrapped boundary
conditions. We solve the optical Bloch equation for each ion in the simulation
as a function of time. Both the simulation and experiment show the initial
Bloch vector rotation, disorder-induced heating, and coherent oscillation of
the rms ion velocity. Detailed modeling of the fluorescence signal makes it
possible to use fluorescence spectroscopy to probe ion dynamics in ultracold
and strongly coupled plasmas.
