Precise Lifetime Measurement of the Cesium $5^2D_{5/2}$ State

We measure the lifetime of the cesium $5^2D_{5/2}$ state using a time-resolved single-photon-counting method. We excite atoms in a hot vapor cell via an electric quadrupole transition at a wavelength of $685\,\mathrm{nm}$ and record the fluorescence of a cascade decay at a wavelength of $852\,\mathrm{nm}$. We extract a lifetime of $1353(5)\,\mathrm{ns}$ for the $5^2D_{5/2}$ state, in agreement with a recent theoretical prediction. In particular, the observed lifetime is consistent with the literature values of the polarizabilities of the cesium $6P$ states. Our measurement contributes to resolving a long-standing disagreement between a number of experimental and theoretical results.