Multiphoton ionization and stabilization of helium in superintense xuv fields

Abstract

Multiphoton ionization of helium is investigated in the superintense field regime, with particular emphasis on the role of the electron-electron interaction in the ionization and stabilization dynamics. To accomplish this, we solve ab initio the time-dependent Schrödinger equation with the full electron-electron interaction included. By comparing the ionization yields obtained from the full calculations with the corresponding results of an independent-electron model, we come to the somewhat counterintuitive conclusion that the single-particle picture breaks down at superstrong field strengths. We explain this finding from the perspective of the so-called Kramers-Henneberger frame, the reference frame of a free (classical) electron moving in the field. The breakdown is tied to the fact that shake-up and shake-off processes cannot be properly accounted for in commonly used independent-electron models. In addition, we see evidence of a change from the multiphoton to the shake-off ionization regime in the energy distributions of the electrons. From the angular distribution, it is apparent that the correlation is an important factor even in this regime.

Direct two-photon double ionization of H2

“…The framework has already been used for single and double ionization studies in helium [17,18,45,46] and the negative hydrogen ion [47].…”

Laser-assisted XUV double ionization of helium: Energy-sharing dependence of joint angular distributions

“…Comprehensive numerical studies on the DI of helium following the absorption of a few XUV photons were carried out by Parker et al [16] starting 15 years ago. Following the 2005 experiment of Hasegawa et al [7], two-photon DI of helium has been the subject of several theoretical studies [15,[17][18][19][20][21][22][23][24][25][26][27][28]. In particular, Zhang et al [26] calculated joint angular distributions (JADs) for two-photon DI by XUV pulses in both the nonsequential (39.5 eV < ω XUV < 54.4 eV) and the sequential ( ω XUV > 54.4 eV) regimes for different energy sharings of the emitted electrons.…”

Laser-assisted XUV few-photon double ionization of helium: Joint angular distributions

“…Despite the complicated nature of the three-particle Coulomb-breakup dynamics in response to the absorption of one [3,4,8,15,20], a few [6,[8][9][10][11][12][13][14][15][16], or many [17,18] photons by helium atoms in their ground state, basic physical principles remain transparent in measured differential helium doubleionization (DI) cross sections. These underlying principles include most importantly angular-momentum, energy, and parity conservation, and selection rules for the interaction of atoms with electromagnetic radiation.…”

“…In such experiments, the momenta of two particles in the final, fully fragmented state, consisting of the helium nucleus and the two released electrons, need to be detected in coincidence. On the theoretical side, the quantitative description of the three-body breakup process has made significant progress over the past two decades [7][8][9][10][11][12][13][14][15][16][17][18], most noticeably due to the development of improved analytical models for the correlated final three-body Coulomb state after the three-particle breakup [19,20] and extensive ab initio calculations made possible by efficient numerical algorithms [21,22] and much improved computational resources.…”