High Precision Linewidth Measurement of Laser-Cooled Atoms: Resolution of the Na3p2P3/2Lifetime 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 $3{}^2{S}_{1/2}\to 3{}^2{P}_{3/2}$ transition with $<0.25\mathrm{}\%$ 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.