Abstract
Using the improved quantitative rescattering (QRS) model, we simulate the correlated two-electron momentum distributions (CMD) for nonsequential double ionization (NSDI) of Ar by near-single-cycle laser pulses with a wavelength of 750 nm at an intensity of 2.8 × 1014 W/cm2. With the accurate cross sections obtained from fully quantum mechanical calculations for both electron impact excitation and electron impact ionization of Ar+, we unambiguously identify the contributions from recollision direct ionization (RDI) and recollision excitation with subsequent ionization (RESI). Our analysis reveals that RESI constitutes the main contribution to NSDI of Ar under the conditions considered here. The simulated results are directly compared with experimental measurements [Bergues et al., Nature Commun. 3, 813 (2012)] in which each NSDI event is tagged with the carrier-envelope phase (CEP). It is found that the overall pattern of both the CEP-resolved and the CEP-averaged CMDs measured in experiment are well reproduced by the QRS model, and the cross-shaped structure in the CEP-averaged CMD is attributed to the strong forward scattering of the recolliding electron as well as the depletion effect in tunneling ionization of the electron from an excited state of the parent ion.
Highlights
Over the past three decades, nonsequential double ionization (NSDI) has been the subject of numerous experimental and theoretical studies
Under the experimental conditions considered here, the maximum collision energy is around 50 eV, which indicates that both recollision excitation with subsequent ionization (RESI) and recollision direct ionization (RDI) contribute to NSDI of Ar
With differential cross sections for electron impact excitation of Ar+ calculated with the stateof-the-art multi-electron B-spline R-matrix close-coupling theory, we simulated the correlated two-electron momentum distributions (CMD) for NSDI of Ar by near-single-cycle 750 nm laser pulses at an intensity of 2.8 × 1014 W/cm2 for carrier-envelope phase (CEP) ranging from 5◦ to 155◦ in steps of 30◦, based on the improved quantitative rescattering (QRS) model
Summary
Over the past three decades, nonsequential double ionization (NSDI) has been the subject of numerous experimental and theoretical studies (for a review, see [1]). The principal underlying physical mechanisms leading to NSDI were initially revealed by the prominent “knee” structure observed in pioneering experiments, in which the yield of doubly charged ions was measured as a function of the laser intensity [2,3]. Since many characteristic structures of that particular process are smoothed out in the total yield of doubly charged ions, these measurements could only give limited insight into the dynamics of laser-electron and electron-electron interaction in NSDI. On the other hand, when the laser intensity is close to or even slightly below threshold, so-called “anti-correlation” has been observed, where back-to-back emission dominates and the two released electrons concentrate in the second and fourth quadrants [8]
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