Isotope shift in xenon by Doppler-free two-photon laser spectroscopy

Isotope shifts and pressure broadening have been measured in the two-photon transition at 249 nm from the 5p 6 1 S 0 ground level of neutral xenon to a J=0 level of the 5p 5 6p configuration (the 2p 5 level in Paschen notation). A continuous-wave tunable dye laser operating at 498 nm with intracavity frequency doubling excited the transition. The work is the first application of Doppler-free laser spectroscopy to a transition involving the ground level of a rare gas. The results show that although no s electron is directly involved in the transition, the field isotope shifts are comparable with those observed in transitions of the type 6s-np.