Two-dimensional electron returning trajectory in nonsequential double ionization by strong-field circularly polarized laser pulses

We investigate the features of electron returning trajectories in recollision-induced nonsequential double ionization by intense circularly polarized laser pulses within a classical ensemble model. We find typical two-dimensional returning trajectories of the first ionized electron that can be decomposed into local circular motion driven by the laser field and overall elliptical motion due to the Coulombic attraction of the parent ion. Such trajectories burst within a narrow time window of less than two laser cycles and end periodically with kinetic energies around the instantaneous ponderomotive energy after many laser cycles, which is very different from the well-known simple one-dimensional returning trajectories in the case of linear laser polarization.