Fig. 4. Expected scaling with the number of cycles.

a, b Ratio between ${\Lambda }_n^2$ and its asymptotic value $A_n^2$ (monochromatic case), as a function of the IR and XUV pulse durations, while keeping fixed ${\sigma }_X=11$ fs and ${\sigma }_{IR}=10T_{IR}$, respectively. Open circles represent the SFA calculation, while the solid lines the model of Eq. (4). The higher the SB order n, the stronger the effect of the finite duration of the pulses. The blue dash-dotted vertical line sets the validity of the approximations used in the theoretical model. The black horizontal line corresponds to the monochromatic limit, while the red dashed line corresponds to the 3τ-convergence. The shaded gray area delimits the region where ${\sigma }_{IR}\le {\sigma }_X$. c Number of IR cycles (also depicted by the false colors) necessary to reach 3τ-convergence as a function of the XUV time duration and the SB order. Floquet states composed of a higher number of SBs and generated by longer XUV pulses require longer times to establish.