Transition frequencies between low-lying energy levels in a single trapped
138Ba+ ion have been measured with laser spectroscopy referenced to
an optical frequency comb. By extracting the frequencies of one-photon and
two-photon components of the line shape using an eight-level optical Bloch
model, we achieved 0.1 MHz accuracy for the 5d 2D3/2 - 6p
2P1/2 and 6s 2S1/2 - 5d 2D3/2 transition
frequencies, and 0.2 MHz for the 6s 2S1/2 - 6p 2P1/2
transition frequency.Comment: 5 pages, 7 figures, submitted to Phys. Rev.