Linewidth of single laser-cooled Mg ion in radiofrequency trap

A single Mg(+) has been successfully trapped and cooled in a small radiofrequency trap. The ion was cooled by using the radiation from a single-frequency ring dye laser whose output was doubled in frequency with an NH(4) (2)H(2)PO(4) temperature phasematched crystal; a power of about 22 muW or less was sufficient for all of the experiments. The ion temperature was estimated by a computer fit of the experimental resonance line profile; the resulting linewidth was compared to previously published Mg(+) 3(2)P(3/2) Hanle-effect linewidths. The result is a temperature of 5(-5) (+15) mK, which is lower than that attained previously.