Selective ionization of Ba and Sr isotopes based on a two-photon interference effect

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Abstract
We show that the zero- and nonzero-nuclear-spin isotopes of Ba and Sr can be excited and ionized at different rates by sequential absorption of radiation from two pulsed laser beams. The selective excitation takes place in a J=0←J=1←J=0 energy-level scheme (where J is the electronic angular momentum), which, depending on the relative polarization of the laser beams, gives totally destructive interference in the absorption rate to the upper J=0 state of a zero-nuclear-spin atom, or a finite but time-dependent rate for population of the upper state for an atom with nonzero nuclear spin. A theoretical explanation of the effect shows the alignment of the nuclear spin as well as the population of the upper state to be time dependent. Isotope ratios were measured in Ba and Sr as a function of laser polarization and delay time, and compared with theory.