M ar 2 00 7 The absolute Frequency measurement of atomic thallium 6 P 1 / 2 → 7 S 1 / 2 transition using optical frequency comb

The Doppler-free spectroscopy of atomic thallium (Tl and Tl) 6P1/2 → 7S1/2 transitions have been observed using two counter-propagating laser beams perpendicular to the atomic beam, and the absolute frequencies of these transitions have been measured to an accuracy of <1 MHz (1 ppb) using optical frequency comb. The hyperfine splittings derived from our results were improved by a factor of 7∼8. The isotope shifts are in agreement with the previous experimental results.