High precision linewidth measurement of laser-cooled atoms: Resolution of the Na 3p P-2(3/2) lifetime discrepancy

We report resolution of the 1% discrepancy between theory and experiment for the lifetime of the first excited state of Na. Determining the atomic lifetime by a novel method, we have measured the natural linewidth of the 3(2)S(1/2) --> 3(2)P(3/2) transition with <0.25% accuracy through precision spectroscopy on an optically prepared sample of ultracold, two-level atoms. The resulting 3(2)P(3/2) lifetime of 16.237(35) ns disagrees with previous time-domain measurements but is in good agreement with recent calculations and a new fast beam result.