Correlated two-electron momentum spectra for strong-field nonsequential double ionization of He at 800 nm

Controlling nonsequential double ionization via two-color few-cycle pulses

Using the classical three-dimensional ensembles, we have demonstrated the controlling of dynamics in nonsequential double ionization (NSDI) of helium by two-color few-cycle pulses. By changing the relative phase of the two pulses, recollisions leading to NSDI can be restricted in a time interval of several hundreds attosecond nearly before the field extremum and as a result, the correlated electron momentum distribution exhibits a so-far unobserved narrow arc-like structure. This structure reveals a novel energy correlation between the two electrons from NSDI by two-color few-cycle pulses.

Manipulating nonsequential double ionization via alignment of asymmetric molecules

Using classical three-dimensional ensembles, we demonstrate that nonsequential double ionization of HeH+ molecules in an intense laser field can be manipulated by controlling the alignment of the molecular axis relative to the laser field. Both the symmetry of the correlated electron momentum spectrum in the direction parallel to the laser field and the total double ionization yield strongly depend on the angle between the molecular axis and the laser field. When the molecular axis is aligned parallel to the laser field, double ionization is most probable and the correlated electron momentum spectrum parallel to the laser field from nonsequential double ionization exhibits the most asymmetry with respect to the minor diagonal.

Probing electron correlation via attosecond xuv pulses in the two-photon double ionization of helium

Recent experimental developments of high-intensity, short-pulse extreme ultraviolet light sources are enhancing our ability to study electron-electron correlations. We perform time-dependent calculations to investigate the so-called "sequential" regime (variant Planck's over 2piomega > 54.4 eV) in the two-photon double ionization of helium. We show that attosecond pulses allow us not only to probe but also to induce angular and energy correlations of the emitted electrons. The final momentum distribution reveals regions dominated by the Wannier ridge breakup scenario and by postcollision interaction.

Classical trajectory diagnosis of a fingerlike pattern in the correlated electron momentum distribution in strong field double ionization of helium

With a semiclassical quasistatic model, we identify the distinct roles of nuclear Coulomb attraction, final-state electron repulsion, and the electron-field interaction in forming the fingerlike (or V-shaped) pattern in the correlated electron momentum distribution for helium double ionization in intense laser field [Phys. Rev. Lett. 99, 263002;Phys.Rev.Lett.99, 263003 (2007)]. The underlying microscopic trajectory configurations responsible for asymmetric electron energy sharing after electron-electron collision have been uncovered, and the corresponding subcycle dynamics is analyzed. The correlation pattern is found to be sensitive to the transverse momentum of correlated electrons.

Recollision excitation, electron correlation, and the production of high-momentum electrons in double ionization

The production of high-momentum electrons in double ionization of helium by near-infrared lasers is investigated using three-dimensional classical ensembles. The nucleus' role is examined by systematically adjusting the nuclear potential. The primary source of the high-energy electrons is found to be backscattering off the nucleus at recollision. Recollision excitation with backscattering of the unbound electron is found to be especially important. It is shown that recollision excitation with ionization before the next field maximum can lead to a correlated electron pair.

Recoil-ion momentum distributions for two-photon double ionization of He and Ne by 44 eV free-electron laser radiation

Recoil-ion momentum distributions for two-photon double ionization of He and Ne (variant Planck's over omega=44 eV) have been recorded with a reaction microscope at FLASH (the free-electron laser at Hamburg) at an intensity of approximately 1 x 10(14) W/cm2 exploring the dynamics of the two fundamental two-photon-two-electron reaction pathways, namely, sequential and direct (or nonsequential) absorption of the photons. We find strong differences in the recoil-ion momentum patterns for the two mechanisms pointing to the significantly different two-electron emission dynamics and thus provide serious constraints for theoretical models.

Strong-field double ionization of Ar below the recollision threshold

Nonsequential double ionization of Ar by 45 fs laser pulses (800 nm) at (4-7)x10;{13} W/cm;{2} was explored in fully differential measurements. Well below the field-modified recollision threshold we enter the multiphoton regime. Strongly correlated back-to-back emission of the electrons along the polarization direction is observed to dominate in striking contrast to all previous data. No effect of Coulomb repulsion can be found, the predicted cutoff in the sum-energy spectra of two emitted electrons is confirmed, and the potential importance of multiple recollisions is discussed.

Laser-induced electron tunneling and diffraction

Molecular structure is usually determined by measuring the diffraction pattern the molecule impresses on x-rays or electrons. We used a laser field to extract electrons from the molecule itself, accelerate them, and in some cases force them to recollide with and diffract from the parent ion, all within a fraction of a laser period. Here, we show that the momentum distribution of the extracted electron carries the fingerprint of the highest occupied molecular orbital, whereas the elastically scattered electrons reveal the position of the nuclear components of the molecule. Thus, in one comprehensive technology, the photoelectrons give detailed information about the electronic orbital and the position of the nuclei.