Distribution of saddle points in circularly polarized fields. Panel (a) shows z (blue) and x (orange) components in a bicircularly polarized fields. Taking an initial momentum p 0 = ( 0.8 , − 0.8 ) for instance, the distribution of roots of Eq. (3) in the complex time plane is presented in panel (b). The contour lines represent the Im [ i S ( t ) ] that pass via all t s ( α ) . Each t s ( α ) is indicated by a white marker. Invalid solutions that do not obey conditions (7) and (8) are indicated by green circles.