Single and double ionization of helium in intense bicircular laser fields

Abstract

The single and double ionization of helium in intense 2ω:ω bicircular laser fields is analyzed with a classical ensemble method. A high-performance computational cluster is utilized to generate high-resolution data and to probe low-rate events. It is found that both counter- and co-rotating fields support rescattering and non-sequential double ionization (NSDI). The effects of scattering off of the ionic core are evident in the single-ionization energy spectra, and the role of the Coulomb potential is clearly visible in the electron momentum distributions. The dynamics of the double ionization processes are investigated by analyzing ionization phase, electron energy and momenta, and rescattering timing. For corotating fields, rescattering is only possible for ionization near the field minimum, placing limits on the efficiency of NSDI. For counterrotating fields, the electron trajectories that contribute to rescattering are found to fall into only three categories (looping, triangular, or a combination of the two), and the contributions from these trajectories is distinguishable in the resulting double-ion electron momentum distributions. This study explores the full range of field amplitude ratios that contribute to the dynamics of rescattering, and therefore provides an overall view of the limitations of using bicircular fields for applications in strong-field physics.