Enhanced multiple-scattering and intra-half-cycle interferences in the photoelectron angular distributions of atoms ionized in midinfrared laser fields

摘要

We investigate the physical mechanisms responsible for fine structure in the photoelectron angular distributions from atoms subject to intense midinfrared laser fields by solving the time-dependent Schrödinger equation in the integral form. By restricting the ionization to a half cycle of the laser field and then propagating the liberated electron wave packet during the laser pulse, we show conclusively that low-energy-momenta structure in the photoelectron angular distribution originates from multiple scatterings of the tunnel-ionized electron with the ion. We also show that two conditions must be satisfied simultaneously in order to observe prominent low-energy features. First, multiple scattering of the tunnel-ionized electron wave packet is necessary. Second, tunnel ionization must dominate over multiphoton ionization. While the first condition is generally satisfied for all laser wavelengths, the second condition is satisfied only for longer laser wavelengths.