We have investigated the recollision dynamics of correlated electron from nonsequential double ionization (NSDI) with 3200 nm laser fields at a wide range of intensities using a full-dimensional classical ensemble method. The numerical results show that for the mid-infrared laser fields, the double ionization probability versus laser peak intensity still displays a much clear “traditional” knee structure representing NSDI. At low intensity, the electron momentum correlated spectrum along the laser polarization direction shows a V-shaped structure; whereas at high intensity, the spectrum exhibits a clearly cross-shaped structure. We demonstrate that both the V-shaped structure and the cross-shaped structure are the results of extremely asymmetric energy sharing of the two electrons at recollision. Moreover, the most prominent contribution to NSDI is from the second-returning trajectory and the first-returning trajectory is significantly suppressed. What’s more, the mechanism of NSDI is from recollision impact ionization (RII) channel as well as recollision-excitation-with-subsequent-ionization (RESI) channel. We find that at low intensity, only the RII channel contributes to V-shaped structure; whereas at high intensity, both the RII and RESI channels have comparable contribution to the cross-shaped structure. Further, we diagnose the recolliding electron and the bound electron separately by tracing the classical trajectories.
Nonsequential double ionization with mid-infrared laser fields