Abstract
The measurement of the absolute frequencies of the 2S→3S of atomic lithium is reported. To reduce systematic effects, we employed a frequency-comb-stabilized excitation laser, a weakly collimated atomic beam, and the cascading 2P→2S 670 nm fluorescence as the signal. The transition frequencies, including two isotopes (6 <sup>,</sup> 7Li), were measured to an accuracy of <330kHz. In comparison with the previous GSI Group experiment, the frequency of the 2S <sub>1/2</sub> →3S <sub>1/2</sub> transition of 7Li is 815̂ 618̂ 181.45(9) MHz, which is improved by a factor of 2. The resultant hyperfine constants of the 3S state and the deduced difference of the nuclear charge radii δ̂rc2̂œ< from the isotope shift are in good agreement with previous results. Since a more straightforward methodology is adopted, our measurement is less model dependent and serves as an independent investigation of the reported transitions. © 2011 American Physical Society.