Investigation of the dynamic Stark effect in aJ=0→1→0three-level system. I. Experiment

The dynamic Stark effect is investigated in a J=0→1→0 three-level ladder system in an atomic beam of natural barium. This system is free of hyperfine structure, which has complicated previous experiments of this type. An intense, actively stabilized cw dye laser was tuned to resonance with the transition between the upper two levels, and a similar, but much less intense, probe laser was scanned through resonance with the transition connecting the lower two levels. Fluorescence arising from transitions out of the middle and upper levels was separately recorded as a function of probe-laser frequency. This allowed us to observe the effects of the strong laser on both the levels which it coupled. The smooth transition from an Autler-Townes doublet to a single light-shifted peak was observed, as well as effects related to coherent population trapping. The resulting profiles were found to be in excellent agreement with theoretical predictions. With a theoretical model extended to incorporate the contributions of the five most abundant isotopes of barium, and other nonideal features of the experiment, it was possible to account for every detail of the observed profiles. Comparing the experimental results with theory also yielded a measurement for the absorption f value for the 6s6p ${\mathrm{}}^1$ $P_1$→6$p^2$ ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ (608.3 nm) transition in ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$.