Potential Barrier Effects in Two-Photon Ionization and High-Order Harmonic Generation in the X-Ray Regime

Anthony F. Starace
The University of Nebraska-Lincoln

Potential barrier effects are well-known features of atomic photoionization cross sections
[see, e.g., A.F. Starace, "Theory of Atomic Photoionization," Handbuch der Physik, 31,
ed. by W. Mehlhorn (Springer-Verlag, Berlin, 1982), pp. 1-121]. I shall present recent
results showing that potential barriers also greatly influence two-photon ionization processes
as well as high-order harmonic generation from plasmas in the soft x-ray regime.
Furthermore, they may allow extension of table-top harmonic generation for atomic targets
into the soft x-ray regime.