Photon flux optimization in three-color multiphoton ionization of uranium atoms

Ionization probability in three color excitation of uranium atoms depends on the photon flux which drives the transition to an autoionizing level. For a proper choice of the flux ratio, the ionization probability is insensitive of the actual fluxes over a considerable range. Thus, the laser intensities used may be lowered by a factor of about 3 as compared to values predicted on the basis cross-sections of the individual transitions. A quantum-mechanical model, based on a detailed ca.culation of population dynamics of the levels in the ionization scheme, predicts the ionization probability as a function of the three-laser intensities. Ionization saturation measurements provide parameters for the model. The theoretical predictions were partially consistent with the experimental results. Ionization probabilities as high as 937. are achievable.