Photoelectron momentum distribution in counter-rotating fields of N_c = 3 is shown in panel (a). Two sample points, as indicated by red marks, are chosen for trajectory analysis. The tunneling time, tunneling exits and the trajectories are shown in panels (b)–(d) [(e)–(g)] for the left (right) sample point, respectively. Green circle in panels (d) and (g) indicates the starting position of trajectories.