Isotope shifts and hyperfine splittings of the 3988-nm Yb i line

We report the first observation to our knowledge of the 6s2 S10-6s6p P11∘ transition (398.8 nm) of 168Yb. The relative position of this spectral line was directly determined by using a laser sideband technique to simultaneously probe pairs of lines. The hyperfine structure of 171Yb and the isotope shifts of 170Yb, 171Yb, and 174Yb were determined to an accuracy of better than 6 MHz and found to differ by as much as 23 MHz from previous results. By using photon-burst spectroscopy to carry out these measurements we obtained subnatural linewidths and fully resolved the 170Yb and 171Yb lines, which otherwise overlap in fluorescence.