Potential Barrier Effects in Multiphoton Ionization Processes

Potential barriers in the effective radial potential experienced by a photoexcited electron are shown to result in dramatic, resonance-like effects in multiphoton ionization processes. In a multiphoton ionization process, such potential barriers may affect not only the final state of the electron (as in single-photon ionization), but also the intermediate- state electron wave packet at energies in the vicinity of the barrier. Such effects have been demonstrated numerically as a function of frequency [1], confirming an experimentally- observed enhancement in two-photon ionization of Xe at a single frequency [2]. We show here that these effects are general by considering the n-photon cross sections (with n$>$2) for ionization of Ar and Xe within a single-active-electron, central-potential model.\\[4pt] [1] L.W. Pi and A.F. Starace, Phys. Rev. A \textbf{82}, 053414 (2010).\\[0pt] [2] V. Richardson \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 013001 (2010).