High-order above threshold ionization spectrum of hydrogen and photoelectron angular distributions

Abstract

The multiphonon ionization of the hydrogen atom resulting from its interaction with an intense and short laser pulse has been investigated theoretically, by solving the time-dependent Schrodinger equation (TDSE) via the state-specific expansion of the time-dependent wavefunction. We report above threshold ionization (ATI) spectra and photoelectron angular distributions (PADS) for photon energies ranging between 2 and 4 eV and for laser intensities up to 2*1014 W cm-2. In agreement with recent experimental observations, for h(cross) omega =2 eV and 3 eV a plateau-like structure was found in the ATI spectra. Furthermore, for high-order ATI peaks the PADS show a variety of side-lobes, including emission at 90 degrees off the laser polarization axis. These results are interpreted in terms of tunnelling, multiphonon absorption and interference phenomena.