Observation of Ba^+np_1/2 and ngj Rydberg series

Abstract

The np1/2 and ngj Rydberg series of the Ba+ ion have been observed, using a multistep laser-excitation scheme. A single photon excites either the np1/2 levels from an initially populated Ba+ 8s1/2 state or the ngj levels from the Ba+ 5fj states. The Ba+ 8s1/2 state is populated directly through two-step laser excitation of ground-state Ba+ ions, and the Ba+ 5fj state is a decay product of neutral-Ba 8snd autoionizing states, which are produced by an analogous two-step excitation of bound 6snd states. We observe no excitation of the np3/2 levels, indicating a zero in the excitation cross section to these levels. Using the quantum defects of the ng series, we are able to extract values for the electric dipole and quadrupole polarizabilities of the Ba2+ core of 10.3(2)a03 and 51(10)a05.