Abstract

Recent studies of multiphoton ionization¹ indicate the presence of an anomalously strong coupling for high Z materials. The principal findings, obtained at intensities up to ~10¹⁶ W/cm², are (1) an unexpectedly strong multiphoton coupling strength resulting in multiple ionization of target atoms, (2) a strong Z-dependence of the coupling, and (3) ion charge state distributions which in some cases resemble those characteristic of Auger cascades. The results of these experiments suggest, for the heavy materials, a multiphoton analog of the collective atomic inner-shell response observed in both single-photon photoionization² and bremsstrahlung.³ The relatively slow decline observed in the abundance of high ion states as Z increases qualitatively corroborates such an interpretation.

© 1984 Optical Society of America