Figure 6. The horizontal thin curves show the total population from equation (11) against the time delay td between the pulses of the double-pulse laser for the laser phase parameter (a) β = zero and (b) β = π with the peak of the first pulse at different times t = tp. Other fixed parameters are Eph = 0.9 eV, α = 106.53 a.u., F0 = 100 kV cm−1, F1 = 3F0 and ${\rm{\Omega }}=1.4744\ast {10}^{-4}$ a.u., The number and positions of peaks in the total population does not change with changes of the laser phase parameter β. This shows that while keeping the other parameters fixed, the number of orbits or the periods of the orbits do not change with the laser phase parameter β. The laser phase parameter β just modulates the peaks, as the spectrum in figure 6(b) is the mirror copy of the spectrum in figure 6(a).The thick curve is the classical period of the closed orbits originating at different times, based on equation (2).
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