Ultracold neutral plasma heating due to resonance excitation

We report electron heating measurements in an expanding ultracold neutral calcium plasma. The plasma is formed by resonantly ionizing calcium atoms in a magneto-optical trap. The 397 nm resonance transition is excited at intensities ranging from 0.2 to 10 times the saturation intensity. We observe an increasing plasma expansion rate due to more rapid electron heating as the intensity of the 397 nm excitation increases. We discuss possible implications for laser-cooling the ions in this ultracold neutral plasma environment.