Direct Frequency Comb Spectroscopy of Trapped Ions

Direct frequency comb spectroscopy of trapped ions is demonstrated for the first time. It is shown that the 4sS1/22-4pP3/22 transition in calcium ions can be excited directly with a frequency comb laser that is up-converted to 393 nm. Detection of the transition is performed using a shelving scheme to suppress the background signal from nonresonant comb modes. The measured transition frequency of f=761905012.7(0.5)MHz presents an improvement in accuracy of more than 2 orders of magnitude. © 2009 The American Physical Society.