Nonrelativistic ionization of the L-shell states in argon by a "relativistic" 1019 W/cm2 laser field -: art. no. 042712

The field ionization cross sections for the L-shell states in argon are presented as measured with pulsed-laser radiation at an intensity of up to 10(19) W/cm(2). For ultrahigh intensities, the photoelectron continuum dynamics will be relativistic. However, the measured charge-state yields for Ar9+ to Ar16+ compare favorably to numerical solutions of the nonrelativistic Schrodinger equation and a widely used Ammosov-Delone-Krainov/WKB tunneling ionization model. The results are interpreted within a two-step, strong-field ionization model, where the initial tunneling ionization process is dominated by nonrelativistic effects while the photoelectron continuum dynamics are strongly relativistic.