Photoelectron angular distributions from the ionization of xenon Rydberg states by midinfrared radiation

Abstract

Angle-resolved photoelectron spectra, resulting from the strong-field ionization of atoms or molecules, carry a rich amount of information on ionization pathways, 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.

Multielectron effects in the photoelectron momentum distribution of noble-gas atoms driven by visible-to-infrared-frequency laser pulses: A time-dependent density-functional-theory approach

“…They exhibit complex structures due to the electron rescattering, similar to the xenon PMD measured using a mid-infrared (24-31 µm) driving laser pulse in Ref. [3].…”

“…9 are well separated, and the m=0 state that is in parallel with the driving-laser field (2p 0 for Ne and 3p 0 for Ar) yields the most photoelectrons. As a result, it is safe to assume that the SAE approximation is valid in the PMD calculation with an infrared driving laser field, in accordance with the recent publications by other groups [3,38]. In Figure 10, we plot the single-electron PMD of the 2p 0 state of Ne and the 3p 0 state of Ar.…”

“…In the previous sections (III A-III C), atoms are driven by a visible (527 nm) linearlypolarized laser pulse. Experimentally, a driving-laser with longer wavelengths (typically near-to mid-infrared) is more commonly used in the momentum spectroscopy [3,15,19].…”

“…Since the X-ray free-electron lasers around the world (such as LCLS in US, SACLA in Japan, and the FLASH in Germany) became operational around 2010, many groundbreaking experiments have been conducted in the field of angle-resolved photoelectron momentum spectroscopy of gaseous atoms, e.g., the orbital-dependent observation of lithium (Li) excited states [1], the two-color, core-excitation of neon (Ne) atoms [2], and the xenon Rydberg states [3], to name a few. Resolutions of the photoelectron momentum distribution (PMD) in these experiments are unprecedentedly high, which has made the detailed comparison with theoretical calculations possible.…”

“…There are various methods to calculate the PMD of atoms, such as the R-matrix theory [4,5], the perturbation approach [6], the strong-field approximation [7,8], and the timedependent Schrödinger equation (TDSE) [9,10]. The PMD of hydrogen atoms has been studied extensively in the past using the TDSE [11][12][13][14], but the PMD of many-electron atoms previously studied was limited by the single-active-electron (SAE) approximation [3,15,16].…”