Lifetime measurement in138Ba+ 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 6p ²P_3/2 level of¹³⁸Ba⁺ 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 τ=(6.31±0.05) ns which is in good agreement with a previous high precision measurement by Andrä. Implications for the possible observation of coherent transient effects in fast ion beams are briefly discussed.