ACCURATE IONIZATION THRESHOLDS OF ATOMS SUBJECT TO HALF-CYCLE PULSES

The evolution of Rydberg states of hydrogen and alkali-metal atoms sub ject to short half-cycle pulses is studied. The convergence of the num erical solutions of the time-dependent Schrodinger equation based on a n expansion of the electronic wave function in a finite basis set of S turmian functions is analyzed in detail. It is shown that the accuracy of such calculations can be established by investigating the stabiliz ation of the transition probabilities with respect to the parameters t hat define the basis set. The dependence of the quantum and classical ionization thresholds on the pulse shape is investigated. The calculat ions are compared with experimental data for various pulse profiles, w hich feature slow or fast rise times. The results show that the ioniza tion thresholds for long pulses are very sensitive to the rise time of the electric field.