Nonsequential Double Ionization of Molecules in Counter-Rotating TwoColor Circularly Polarized Laser Fields

Nonsequential double ionization (NSDI) of N2 molecules in counter-rotating two-color circularly polarized fewcycle laser fields is investigated by the classical ensemble method. The results show that for the determined laser intensity, the yield of NSDI decreases significantly with the increasing laser wavelength, which is caused by the diffusion effects of electron wave packets. It is also found that the ionization mechanism of NSDI is affected by the laser wavelength. Collision excitation ionization becomes increasingly dominant with the rising laser wavelength, which is related to the return trajectory and return energy of the first electron. At the same time, the electron momentum distribution of NSDI is discussed in this paper. The electron momentum distribution varies significantly with the laser wavelength, and the longer laser wavelength leads to clearer "rotating three-lobed fan-like" structures.