language: en

[Confidential: not for distribution. Submitted to IOP Publishing for peer review]

30 November 2009

[LETTER TO THE EDITOR]

Influence of autoionizing states on the pulse-length dependence of strong-field Ne + photoionization at 38.4 eV

Linda Hamonou, Michael A. Lysaght and Hugo W. van der Hart
Centre for Theoretical Atomic, Molecular and Optical Physics, Queen's University Belfast,
Belfast BT7 1NN, United Kingdom

Abstract. Using the time-dependent R-matrix approach, we investigate ionization of ground-state Ne + , irradiated by laser light with a photon energy of 38.4 eV at intensities 10 13 W cm −2 , 2 × 10 13 W cm −2 and 10 14 W cm −2 as a function of pulse length. Although the photon energy is below the threshold for single-photon ionization, we obtain a significant contribution from single-photon ionization to the ionization probability due to the finite duration of the pulse. The two-photon ionization rates deduced from the calculations are consistent with those obtained in R-matrix-Floquet rate calculations. The ionization probability oscillates with pulse length, which is ascribed to population and depopulation of autoionizing states just above the Ne 2+ ground state, reached after absorption of a single photon. At an intensity of 10 14 W cm −2 , pulse lengths longer than 50 cycles are required for two-photon ionization to dominate the ionization probability.

PACS numbers: 32.80.Rm, 32.30.Rj

[Letter to the Editor 2]