Multiply charged ions induced by multiphoton absorption in rare gases at 0.53 μm

Up to quadruply charged ions are induced in Xe atoms by a 50-psec laser pulse at 0.53 {μ}m in the 10¹² W cm^-2 range. The mechanism of the formation of Xe²⁺ ions is elucidated. In the lowest intensity range, Xe²⁺ ions are produced by direct 15-photon absorption from the ground state of the atoms, while at a higher intensity Xe²⁺ ions are produced by a stepwise process via Xe⁺ ions. These two processes take place at distinctly different intensities. A kinetic model using rate equations affords a good fit with experimental results. Moreover, for the first time it was possible to obtain the multiphoton ionization cross sections related to the two-electron removal from Xe atoms, as well as the one-electron removal from Xe⁺ ions.