Radiative lifetimes of theSandDRydberg levels of Na

We have determined the radiative lifetimes of the $n=5-13\mathrm{}$, $s$ and $d$ states of Na by pumping the desired level with two resonant photons derived from two dye lasers excited by the same ${\mathrm{N}}_2$ laser. The lifetimes increase approximately as the cube of the effective quantum number, and are in good agreement with a Coulomb-approximation calculation.