Angle-resolved photoelectron spectra, resulting from the strong-field ionization of atoms or molecules, carry a rich amount of information on ionization athways, electron dynamics, and the target structure. We have investigated angle-resolved photoelectron spectra arising from the nonresonant ionization of xenon Rydberg atoms in the multiphoton regime, using intense midinfrared radiation from a free-electron laser. The experimental data reveal a rich oscillatory structure in the low-order above-threshold ionization region. By performing quantummechanical and semiclassical calculations, the observed oscillations could be well reproduced and explained by both a multiphoton absorption picture as by a model invoking electron wave-packet interferences. Furthermore, we demonstrate that the shape and orientation of the initial Rydberg state leaves its own fingerprint on the final angular distribution.

Phys. Rev. A

Huismans, Y., Rouzée, A., Gijsbertsen, A., Logman, P. S. W. M., Lépine, F., Cauchy, C., … Vrakking, M. J. J. (2013). Photoelectron angular distributions from the ionization of xenon Rydberg states by midinfrared radiation. Phys. Rev. A, 87(3, Article number: 33413), 1–10. doi:10.1103/PhysRevA.87.033413