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.

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Journal Phys. Rev. Lett.
Citation
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.