Abstract
The absolute frequency measurement of thallium 6P 1/2 → 7S 1/2 transitions using a self-referencing optical frequency comb is reported. Our results can be used as a benchmark for the accurate wave-function calculations of heavy atoms, and then improve the calculations of the atomic parity-nonconservation amplitude. The frequency centers have been precisely determined by the Doppler-free saturation spectroscopy utilizing a pair of the counterpropagating laser beams intersecting with a thallium atomic beam. We have achieved the absolute frequency determination of the transition with an accuracy of 350 kHz. The isotope shift and hyperfine splittings are also deduced from our results. The hyperfine splittings of the 7S 1/2 state are improved to sub-MHz accuracy. Meanwhile, the nuclear isotopic changes resulting from the 7S 1/2 and 6P 1/2 hyperfine anomalies are in agreement with earlier measurements. © 2012 American Physical Society.