Single- and double-photoionization data of Na and K corroborate the existence of a universal scaling law for the ratio

Using monochromatized synchrotron light and the ion time-of-flight method to detect the singly and doubly charged sodium and potassium ions, we have investigated the relative double-photoionization cross-section ratios of Na from 52.4 to 150 eV and of K from 36.5 to 170 eV. We found that both followed a scaling law previously observed for Li and Be, which describes the photon energy dependence of that ratio and allows one to estimate its absolute value. We have also obtained the relative single- and double-photoionization cross sections for Na and K.