Cross-channel contributions to vortex patterns in photoionization by a pair of counter-rotating circularly polarized attosecond pulses

We theoretically investigate the cross-channel contributions to vortex patterns in photoionization of ${\textrm{He}^{+}}$ by a pair of left-right circularly polarized attosecond pulses by numerically solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE). It is found that the contribution of the ionization cross-channel only worked with a short time delay and the ionization cross-channel will lead to the difference in the brightness of the vortex patterns. The sensitivity of the vortex pattern to the time delay can be employed to control the ionized electron distributions by adjusting the time delay between two laser pulses. These phenomena can be explained by the attosecond perturbation ionization theory