Enhanced asymmetry in few-cycle attosecond pulse ionization of He in the vicinity of autoionizing resonances

Abstract

By solving the two-active-electron, time-dependent Schrödinger equation in its full dimensionality, we investigate the carrier-envelope phase (CEP) dependence of single ionization of He to the He + (1s) state triggered by an intense few-cycle attosecond pulse with carrier frequency ω corresponding to the energyhω = 36 eV. Effects of electron correlations are probed by comparing projections of the final state of the two-electron wave packet onto field-free highly correlated Jacobi matrix wave functions with projections onto uncorrelated Coulomb wave functions. Significant differences are found in the vicinity of autoionizing resonances. Owing to the broad bandwidths of our 115 and 230 as pulses and their high intensities (1-2 PW cm −2 ), asymmetries are found in the differential probability for ionization of electrons parallel and antiparallel to the linear polarization axis of the laser pulse. These asymmetries stem from interference of the one-and two-photon ionization amplitudes for producing electrons with the same momentum along the linear polarization axis. Whereas these asymmetries generally decrease with increasing ionized electron 4 2 kinetic energy, we find a large enhancement of the asymmetry in the vicinity of two-electron doubly excited (autoionizing) states on an energy scale comparable to the widths of the autoionizing states. The CEP dependence of the energyintegrated asymmetry agrees very well with the predictions of time-dependent perturbation theory (Pronin et al 2009 Phys. Rev. A 80 063403).

Carrier-envelope-phase-induced asymmetries in double ionization of helium by an intense few-cycle XUV pulse

“…For single ionization of an atom by a few-cycle XUV pulse, a PT analysis [11] provides an ab initio parametrization of the ionized electron AD in terms of the key parameters of the process: the CEP of the pulse, the pulse polarization, and the electron momentum direction. This parametrization [11] for XUV pulse photoionization of He describes accurately numerical results obtained by solving the time-dependent Schrödinger equation (TDSE) [12][13][14]. In general in the PT regime, the AD asymmetry originates from interference of first-and second-order PT transition amplitudes to continuum states with the same energy E but different parities [11].…”

“…For linear polarization of the pulse, our PT parametrization is in excellent agreement with results of solutions of the full-dimensional, two-electron TDSE, validating the PT approach. These numerical results show that the normalized asymmetry in DPI significantly exceeds that for single ionization of He for I = 1-2 PW/cm 2 [12,13] and are comparable to that for single ionization plus excitation of He to He + (2s,2p) [14]. We have also investigated the CEP dependence of the AD for the special case of orthogonal geometry for which the first-order amplitude vanishes, providing a means to directly investigate the CEP dependence of the second-order PT amplitude.…”

“…Our numerical method for obtaining C (φ) is described in Ref. [13], which treats single ionization of He for a pulse carrier frequency ω = 36 eV. We bypass the necessity of including correlation in the field-free double-continuum states by waiting ≈20 a.u.…”

Electron Vortices in Photoionization by Circularly Polarized Attosecond Pulses

“…Our method uses the finite-element discrete-variable representation combined with the real-space-product algorithm [10] as well as Wigner rotation transformations at each time step from the laboratory frame to the frame of the instantaneous electric field [11,12]. We extract the triply differential probability (TDP) [13] for single ionization of He to He þ ð1sÞ from the wave packet ΨðT þ τÞ (i.e., after the end of the two pulses) by projecting ΨðT þ τÞ onto correlated field-free Jacobi matrix wave functions [14]. The TDP, d 3 W=d 3 p ≡ W ξ 1 ξ 2 ðpÞ, for single electron ionization to the continuum with momentum p ≡ ðp; θ; φÞ is For our pulse parameters, first-order perturbation theory (PT) applies.…”

Nonlinear Dichroism in Back-to-Back Double Ionization of He by an Intense Elliptically Polarized Few-Cycle Extreme Ultraviolet Pulse

“…In these works for atoms the three-dimensional time-dependent Schrödinger equation (TDSE) is solved using the single-active-electron approximation. General formulations for single ionization of an atom [25] and double ionization of He [29] by an arbitrarily polarized, few-cycle XUV pulse using perturbation theory (PT) have been validated numerically only for the case of a linearly polarized pulse [29][30][31][32] owing to its axial symmetry, which reduces the numerical effort. None of these many prior numerical investigations has addressed the challenging six-dimensional problem of a two-electron system interacting with an arbitrarily polarized XUV pulse.…”