Absolute frequency and isotope shift measurements of mercury 1S0–3P1 transition

We report the measurement of the absolute frequencies of the 6s2 1S0−6s6p 3P1 transition (253.7 nm) and the relevant isotope shifts in five mercury isotopes 198Hg, 199Hg, 200Hg, 202Hg, and 204Hg. The Doppler-free saturated absorption measurements were performed in an atomic vapour cell at room temperature with a four-harmonic generated (FHG) continuous-wave (cw) laser digitally locked to the atomic transition. It was referenced with a femtosecond optical frequency comb synchronized to the frequency of local representation of the International Atomic Time to provide traceability to the SI second by the 330 km-long stabilized fibre optical link. The transition frequencies and isotope shifts have been determined with an accuracy of a few hundred kHz, at least one order of magnitude better than any previous measurement. By making a King plot with the isotope shifts of 6s6p 3P2−6s7s 3S1 transition (546 nm) we determined the accurate value of the ratio of the electronic field-shift parameters E546/E254 and estimated the electronic field-shift term E254.