Fig. 1. Schematic illustration of ionization process of hydrogen atom

Fig. 2. Vortex-shaped momentum distributions of hydrogen atom. (a)-(c) ‘Right/left’ polarization for two time-delayed pulses (first is right circularly polarized and second is left circularly polarized); (d)-(f) ‘left/right’ polarization for two time-delayed pulses

Fig. 3. Vortex-shaped momentum distributions of hydrogen atom when dynamic Stark effect is considered. (a)-(c) ‘Right/left’ polarization for two time-delayed pulses; (d)-(f) ‘left/right’ polarization for two time-delayed pulses. Laser pulses parameters are same as in Fig. 2

Fig. 4. Transition of vortex-shaped momentum distributions from α=0 to α=0.04. (a) α=0 (vortex arms numbered as 1, 2, 3, 4); (b) α=0.04 (arrow illustrating corresponding shift of peak position of second vortex arm); (c) variation of peak intensity of each arm; (d) variation of polar angle of each arm

Fig. 5. Time evolution of different kinds of phases. (a)-(d) Stark phases for α=0.01, 0.02, 0.03, 0.04; (e)-(h) total phase (semiclassical phase+Stark phase) for each vortex arm; (i) comparison of total phases with (solid line) and without (dashed line) Stark effect for each vortex arm

Fig. 6. Vortex-shaped momentum distributions reproduced by integrating between 2 o.c and 8 o.c. (a) α=0.04; (b) pulse envelope function F(t) is unit constant