Frustrated nonsequential double ionization of Ar atoms in counter-rotating two-color circular laser fields

We theoretically investigate the frustrated double ionization (FDI) of Ar atoms with counter-rotating two-color circular (CRTC) laser fields using the three-dimensional (3D) classical ensemble method. Our results show that the FDI probability depends upon the intensity ratio of the CRTC laser fields. The FDI event accompanied with the recollision excitation with subsequent ionization is prevalent and three pathways exist in FDI processes driven by CRTC laser fields. The momentum distribution of a recaptured electron at the ionization time after recollision indicates that the momentum being close to the vector potential is a necessary condition for FDI events to occur. In addition, the recaptured electron most probably transitions to a Rydberg state of which the quantum number is ten in the CRTC fields.