Plateau in above threshold ionization spectra

We present photoelectron energy spectra for the rare gas atoms in strong 40 fs, 630 nm laser pulses. A new property in the above threshold ionization distribution is described, namely, a plateau. Numerical calculations using one- and three-dimensional models suggest that at least in part this is a one-electron effect. All rare gas atoms investigated show similar behavior, indicating that the plateau in above threshold ionization is a universal phenomenon. We discuss a simple mechanism possibly responsible for the plateau.