Effects of initial electronic state on vortex patterns in counter-rotating circularly polarized attosecond pulses

We theoretically investigate the effects of different electronic states as the initial state on the vortex patterns in photoelectron momentum distributions (PMDs) from numerical solutions of the two-dimensional (2D) time-dependent Schrödinger equation (TDSE) of He + with a pair of counter-rotating circularly polarized attosecond pulses. It is found that the number of spiral arms in vortex patterns is equal to the number of the absorbed photons when the initial state is the ground state. However, the number of spiral arms in vortex patterns is always two more than the number of the absorbed photons when the initial state is the excited state. This sensitivity is attributed to the initial electron density distribution. In addition, we have demonstrated the PMDs for different initial electronic states with the same wavelengths and analyzed their corresponding physical mechanisms. It is illustrated that the method presented can be employed to effectively control the distribution of the electron vortices.