Characterization of ytterbium resonance lines at 649 nm with modulation-transfer spectroscopy

We report modulation-transfer spectroscopy (MTS) on the 6s6pP03↔6s7sS13 transition in neutral ytterbium (Yb) isotopes in a hollow cathode lamp. The MTS dispersive signals show an effective linewidth of 70 MHz, contributed primarily by the pressure broadening. MTS has demonstrated the capability of completely resolving all isotopic lines, except the one in low-abundance Yb168. Frequency measurements of the isotope-stabilized laser are performed using an optical comb, and systematic shifts therein are corrected. We have examined the relative isotope shifts, and the hyperfine constants for the 6s7sS13 state are given as A(Yb171)=6837.83(19) MHz, A(Yb173)=-1891.46(7) MHz and B(Yb173)=-0.62(16) MHz. Our results are in reasonable agreement with previously reported values and essentially resolve the existing discrepancies.