"Nonrelativistic" ionization of the L-shell states in argon by a "relativistic" 10(19) W/cm(2) laser field - art. no. 042712

The field ionization cross sections for the L-shell states in argon are pre sented as measured with pulsed-laser radiation at an intensity of up to 10( 19) W/cm(2). For ultrahigh intensities, the photoelectron continuum dynamic s will be relativistic. However, the measured charge-state yields for Ar9to Ar16+ compare favorably to numerical solutions of the nonrelativistic Sc hrodinger equation and a widely used Ammosov-Delone-Krainov/WKB tunneling i onization model. The results are interpreted within a two-step, strong-fiel d ionization model, where the initial tunneling ionization process is domin ated by nonrelativistic effects while the photoelectron continuum dynamics are strongly relativistic.