Lifetime measurements of individual hyperfine levels using localized Doppler tuning in laser excitation of fast ions

Lifetimes of each hyperfine level of the 6p ${}_{}{}^4{}_{}{}^{}P_{5/2}^{}{}_{}{}^{}$ state of singly charged ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ have been measured using laser excitation of a fast-ion beam. The collinear laser- and ion-beam arrangement was used to achieve high spectral resolution, and transitions to each hyperfine level were locally Doppler tuned into resonance between a pair of post-accelerating electrodes. Decay to the 6$s^4$ $P_{5/2}$ state was observed through a monochromator immediately after the post-acceleration field, and cascade-free lifetimes were then determined by mechanically varying the distance between the excitation and observation points. Depletion of close-lying hyperfine levels prior to the excitation region was necessary in ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ to sufficiently isolate transitions for these measurements. These results form the first set of lifetime measurements for each hyperfine level within a particular J state of an atomic ion. Although no variation in lifetime with F quantum number was detected outside of the determined error bars, application to studies of hyperfine-induced mixing is discussed.