Lifetime measurement in 138Ba+ using superimposed ion and laser beams

As a feasibility test for nanosecond time resolution in the superimposed beam geometry, we remeasured the lifetime of the 6p2Psub(3/2) level of 138Ba+ by a new technique. Merging an accelerated ion beam with an argon laser beam, optical resonance was achieved over a very short path length by Doppler tuning the ion velocity within a short post acceleration zone. The final results is tau = (6.31 +- 0.05)ns which is in good agreement with a previous high precision measurement by Andrae. Implications for the possible observation of coherent transient effects in fast ion beams are briefly discussed. (orig.)