Double photoionization near threshold

The photon energy region near the double-ionization threshold is characterized by the simultaneous - not sequential - emission of the two electrons. By comparing the photon-energy dependence of our measured double-to-single photoionization ratios for lithium and beryllium to the ratios for helium, sodium, and molecular hydrogen, we have found a simple scaling law, which allows us to predict the double-to-single photoionization ratios for other elements.