Ejected-Electron Angular Distribution in Multi-Photon Ionization of Atomic Hydrogen by Ultrashort High-Intensity Laser Pulses

Abstract

We have studied the multi-photon ionization of atomic hydrogen by an intense attosecond laser pulse. We numerically integrate the time-dependent Schrodinger equation by propagating the initial H(1s) state after the onset of the laser pulse using the Crank-Nicolson algorithm. When the pulse is over, we extract the angular distribution of the ejected electrons from the time-propagated wavefunction. For few-cycle 800 nm laser pulses of peak intensities ranging between 1013 and 1015 W/cm2, the photoelectron spectrum is dominated by a set of above-threshold resonances, with the lowest resonance around 0.35 eV corresponding to the nine-photon ionization of the hydrogen atom. In contrast to the standard single-photon ionization process, where the angular distribution is a simple cos2(0) function, many more anisotropy parameters need to be accounted for to describe the ejected photo-electrons. Corresponding experiments are currently being performed in Brisbane (Australia) on hydrogen and Heidelberg (Germany) on Li. Where possible, comparison with experimental data will be made.