Figure 4

(a) as in Fig. 2a. waveguide with amplitude \({q}_{0}=80\mathrm{\mu m}\); leakages around the high curvature points and emitted rays which are reminiscent of the tunneled ATI electrons. Dotted green and purple arrows indicate the "ATI electrons" with the highest kinetic energies that are emerging from the vicinity of two high-curvature sections, and are labeled with their energies. Red and cyan dotted arrows indicate "ATI electrons" with low kinetic energies and are labeled with these energies. (b) calculated "drifting kinetic energy" as a function of the leakage position ("ionization time") according to the semiclassical model and with the assumption of zero velocity at the tunneling exit. The vertical arrows from 4b to 4a show the relations between the drifting energy and the position (instant) of ionization. Green and purple solid and dashed lines are parallel to the trajectories of the most energetic "ATI electrons" and are tangential to the waveguide at the two possible exit points. The gray curves show the calculated critical radius \({r}_{c}\) ,which is equivalent to the tunneling exit point.