New technique for measuring excited-state lifetimes in ions using rapid Doppler switching

A new and accurate method for measuring lifetimes of excited ionic states is described. The method employs selective laser excitation and rapid Doppler tuning to convert the spontaneous exponential decay of the excited state into a spatial variation of fluorescence intensity. The technique has been tested on the $6p {}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^o{}_{}{}^{}$ Ba ii level and our final result of 6.35±0.09 nsec is in excellent agreement with previous high-precision measurements. The method should make it possible to routinely achieve 1 percent accuracy measurements of ionic lifetimes longer than a lower limit of a few nanoseconds, set by transit-time broadening and ion-beam velocity spread.