The asymptotic velocity distribution of electrons ionized in half-cycle-pulse excitation of high Rydberg states (n = 34), placed in a static electric field, is studied using electron velocity-map imaging. At weak half-cycle pulse strengths, the electrons escape over the saddle point in the potential. For strong half-cycle pulses, the electrons are emitted in the direction of the field kick. The much slower and less intense half cycle of opposite polarity, which necessarily follows the main half-cycle pulse, strongly affects the momentum distribution and reduces the excess energy of the electrons significantly.

Phys. Rev. Lett.

Wetzels, A, Gürtler, A, Noordam, L. D, Robicheaux, F, Dinu, C, Muller, H. G, … van der Zande, W. J. (2002). Rydberg state ionization by half-cycle-pulse excitation: strong kicks create slow electrons. Phys.Rev.Lett., 89(Article number: 273003), 1–4.