Controlling Below-Threshold Nonsequential Double Ionization via Quantum Interference

Abstract

We show through simulation that quantum interference in nonsequential double ionization can be used to control the recollision excitation with subsequent ionization (RESI) mechanism. This includes the shape, localization, and symmetry of RESI electron-momentum distributions, which may be shifted from a correlated to an anticorrelated distribution or vice versa, far below the direct ionization threshold intensity. As a testing ground, we reproduce recent experimental results by employing specific coherent superpositions of excitation channels. We examine two types of interference, from electron indistinguishability and intracycle events, and from different excitation channels. These effects survive focal averaging and transverse-momentum integration. DOI: 10.1103/PhysRevLett.116.143001 Correlation and anticorrelation have been extensively studied in strong-field, laser-induced nonsequential double ionization (NSDI). Particularly with the Cold Target Recoil Ion Momentum Spectroscopy technique, information about the electron momenta has become experimentally accessible since the early 2000s. Several features in these distributions provide information about the type of interaction by which NSDI occurs, and the physical mechanisms behind it. It is commonly accepted that NSDI results from the laserinduced inelastic recollision of an electron with its parent ion [1]. If the driving-field intensity is high enough, upon recollision the first active electron releases a second electron by electron-impact (EI) ionization. In contrast, for the socalled below-threshold intensities, the kinetic energy transferred from the first electron to the core is not sufficient to free the second electron. Instead, the recolliding electron imparts only enough energy that the second electron is excited and then ionized with a time delay. This mechanism is known as recollision excitation with subsequent ionization (RESI).Over the years, the prevalent view has been that, in EI, the two electrons will exhibit correlated momenta as a consequence of their being released simultaneously. In contrast, for RESI, back-to-back emission will occur due to the time delay between recollision of the first electron and ionization of the second electron. This view has been backed using classical models, which have reproduced many of the key features encountered in experiments (for reviews, see Ref.[2]). Such models also exhibit excellent agreement with the outcome of other methods, such as the full solution of the time-dependent Schrödinger equation [3] and the strong-field approximation (SFA) [4-6]. The abovementioned studies, performed for EI, suggested that quantum mechanical features such as interference will not survive integration over momentum components perpendicular to the laser-field polarization and focal averaging, which is the typical scenario in NSDI experiments. These conclusions were then extrapolated to RESI without much evidence.Classical models have also successfully reproduced the anticorrelated behavior observed in early RESI experim...

Role of high ponderomotive energy in laser-induced nonsequential double ionization

“…Several theoretical models have been proposed to explain the general features of RESI [13,[15][16][17][18][19], however, no clear conclusion exists about the role of Coulomb effects, depletion of the excited state, and on excitation channels. When considering results obtained using ultrashort pulses, the pattern is largely defined by depletion effects [20][21][22], contributions of doubly excited states [23], soft recollisions [24], and quantum interferences of different excitation channels [25].…”

Non-sequential double ionization with near-single cycle laser pulses

“…In the context of strongly-driven Ar, the above described 1D model attributed the cross-shaped pattern of the correlated electron momenta to the delayed pathway of double ionization 7, 8 . A quantum mechanical calculation, which neglects the Coulomb potential, was used to refine the contribution of the delayed pathway of double ionization to the cross-shaped correlated electron momenta pattern 12 . This calculation identified the key role that the symmetry of the excited state plays in the final shape of the correlated momenta.…”

Above-threshold ionization of helium in the long-wavelength regime: Examining the single-active-electron approximation and the two-electron strong-field approximation

“…For two-electron systems, the SFA has been extensively used in the studies of double ionization (see, e.g., Refs. [14,17,[22][23][24][25]).…”

“…The SFA, also known as the Keldysh-Faisal-Reiss theory [10][11][12], and its modified versions have been extensively applied to investigate both one-electron and two-electron dynamics (see, e.g., Refs. [13][14][15][16][17][18][19][20][21][22][23][24][25]). To our knowledge, the SFA has not been applied for the description of the channel-resolved high-order ATI spectra.…”