Figure 3: Shifts of peak maxima as a function of time. (a) ionization: the peak centers of the px (light blue squares) and py (dark blue circles) signals. Linear fits are included as solid lines in the respective colors. (b) experiment: the shifts of peak centers of the 3p, the 4s, and the 1.06 eV peaks as a function of delay time. Linear fits are included as solid lines in the respective colors. The numbers in parentheses denote the binding energies at zero pump-probe delay, as determined by a linear fit to the temporal development of the binding energies of each peak. These binding energies have been used as the starting point against which the shifts are measured.