Time-resolved collinear fast-beam laser spectroscopy has been used to measure the lifetime of the T=23 537 ${\mathrm{cm}}^{\mathrm{-}1}$, J=9/2 odd-parity [abbreviated as (23 537)${\mathrm{°}}_{9/2}$] level in Nd ii. Nanosecond pulsed excitation was achieved with the Doppler switching technique. The fast ions were selectively excited from the metastable 4${\mathit{f}}^4$5d ${}_{}{}^6{}_{}{}^{}$${\mathit{K}}_{9/2}$ level to the (23 537)${\mathrm{°}}_{9/2}$ level by the light of a cw dye laser. The decay of the resonance fluorescence photons emitted in the transition to the ground 4${\mathit{f}}^4$6s ${}_{}{}^6{}_{}{}^{}$${\mathit{I}}_{7/2}$ level, as a function of the flight distance, was observed. The decay length was scaled into the decay time by the ion velocity, which was determined using the optical resonance itself. The lifetime is 27.7(9) ns.

• Received 25 July 1990

DOI:https://doi.org/10.1103/PhysRevA.43.1451