Ionization of very-high-nRydberg atoms by half-cycle pulses in the short-pulse regime

The ionization of potassium Rydberg atoms with $n\sim 388$ and $n\sim 520$ by pulsed electric fields whose durations, which range from ∼ 2 to ∼ 110 ns, span the transition from the short-pulse to the long-pulse regime is investigated experimentally and the data compared with the results of classical trajectory Monte Carlo calculations. We observe excellent agreement between theory and experiment providing a benchmark test for the validity of the classical limit of ionization. Very-high-$n$ atoms provide an excellent tool with which to probe the response of atoms to pulsed electric fields in the short-pulse regime.