Multiphoton ionization of xenon with 100-fs laser pulses

Abstract

Seven-photon ionization of xenon is investigated for the first time with 100-fs, very intense (1.7\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$) pulses. The electron spectra show a large number of peaks due to above-threshold ionization. Because of the short pulse duration, large threshold shifts (up to 5.6 eV) are directly observable in the electron spectra. The magnitude of the ionization signal reveals that the ionization probability is much lower than expected at such a high intensity. By a linking of the observed shift to the laser intensity, the latter can be obtained with high accuracy.