Electron Energy Spectra from Intense Laser Double Ionization of Helium

Lafon, Robert E.; Chaloupka, J. L.; Sheehy, B.; Paul, P.; Agostini, Pierre; Kulander, K. C.; DiMauro, Louis F.

doi:10.1103/physrevlett.86.2762

Cited by 104 publications

(61 citation statements)

References 23 publications

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“…The field acceleration make the sum momentum increase. The maximum energy for an electron in the double ionization process is about 4U p [23], from Eq. (6), assuming the two emission electron have the same energy, we can obtain the maximum sum momentum |P + | max ≃ 8 a.u..…”

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“…On the other hand, from Fig. 1, we see that the maximum momentum of both electron is about 4.5 a.u.,which is consist with the electron-ion coincidence experiment observation of helium [23], in which the maximum energy of emission electron in NSDI process is 4U p , since the perpendicular component of momentum is small, the maximum momentum component in the polarization direction can be approximate obtained as P z max = 8U p ≃ 4 a.u..…”

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“…During the first ten optical cycles the electric field amplitude is constant, and then the field is switched off using a cos 2 envelope during three cycles, and during the last two optical cycles the electrons is free from the electric field. The wavelength is λ = 780 nm, which is so chosen to match the experiment [2,23], and the intensity of laser is I = 1 × 10 15 W/cm 2 which is right at the 'knee' region of the double ionization of helium. 10 6 or more initial points are randomly distributed in the parameter plane −π/2 < ωt 0 < 3π/2, v 1x0 > 0 for the outer electron and in the microcanonical distribution for the inner electron.…”

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Correlated electron emission in laser-induced nonsequence double ionization of helium

Liu

Chen

2002

Phys. Rev. A

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In this paper, we have investigated the correlated electron emission of the nonsequence double ionization (NSDI) in an intense linearly polarized field. The theoretical model we employed is the semiclassical rescattering model, the model atom we used is the helium. We find a significant correlation between magnitude and direction of the momentum of two emission electrons, and give a good explanation for this striking phenomenon by observing the classical collisional trajectories. We argue that this correlation phenomenon is universal in NSDI process, as revealed by the recent experiment on the argon.PACS numbers: 32.80. Rm, 42.50.Hz, The excessive double ionization observed in Helium experiments [1-3] draws much attention to the multipleelectron dynamics in the laser-atom interaction. In these experiments the single ionization of He in a linearly polarized field is accurately predicted by the single active electron (SAE) approximation [2], well described by the Ammosov-Delone-Krainov (ADK) tunnelling theory [4]. However, the case of double ionization is more complicated. In the regime of very high intensities (I > 10 16 W/cm 2 ) where strong double ionization occurs, the double ionization keeps in good agreement with the sequential SAE models as that in the lower intensities regime(I < 10 14 W/cm 2 ). The double ionization deviates seriously from the sequential SAE model and shows a great enhancement in a "knee" regime [(0.8-3.0) × 10 15 W/cm 2 ]. This surprising large yields of the double ionization obviously indicates that the sequential ionization is no longer the dominating process in this regime and the electron-electron correlation has to be taken into account. Intense efforts to model the twoelectron process of the double ionization in a laser field have reproduced the main feature of the knee structure in the double ionization yield as a function of laser peak intensity and, moreover, yielded quantitative agreement with the experiments in some cases [5,6].The physical mechanism behind this nonsequential process is, however, still debatable. Both the "shake-off" * Email: fu libin@mail.iapcm.ac.cn model and the "recollision" model are suggested to describe the electron's correlation [1,3,7,8]. However, none of the two nonsequence double ionization (NSDI) mechanisms can completely explain the experimental observations. For the "shake-off" model, it can not give the reason for the decrease in the double ionization yields as the polarization of the laser field departs from linear [9-11]. In the "recollision" model, the returning electrons are known to have a maximum classical kinetic energy of ∼ 3.2U p (U p = e 2 F 2 /4m e ω 2 ), so one can determine a minimum intensity required for the rescattering electron to have enough energy to excite the inner electron. But the double ionization yields observed in experiments has no such an intensity threshold. In fact, the double ionization process is rather complicated and subtle, both of the two NSDI processes and the sequential ionization have contributions ...

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Correlated electron emission in laser-induced nonsequence double ionization of helium

Liu

Chen

2002

Phys. Rev. A

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“…Ratios of double to single ionization and electron energy distributions for double ionization (partly integrated over emission angles for low electron energies) have been reported [15][16][17][18] along with experiments, where one momentum component of one emerging electron was measured in coincidence with the full momentum vector of the recoiling target ion providing information about the correlated momenta of both emitted electrons along the laser polarization direction [19,20]. Here, for NS double ionization of Ar by 0.38 and 0.2 PW/cm 2 , 780 nm pulses at a pulse length of 220 and 25 fs, respectively, detailed information on the momentum sharing between both ejected electrons was obtained, which sensitively depends on the recollision dynamics.…”

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Strongly directed electron emission in non-sequential double ionization of Ne by intense laser pulses

Moshammer

Ullrich

Feuerstein

et al. 2003

J. Phys. B: At. Mol. Opt. Phys.

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Double ionization of Ne by 25 fs, 1.0 PW/cm 2 laser pulses has been explored in a kinematically complete experiment using a "Reaction Microscope".Electrons are found to be emitted into a narrow cone along the laser polarization (ε), much more confined than for single ionization, with a broad maximum in their energy distribution along ε. Correlated momentum spectra show both electrons being ejected into the same hemisphere, in sharp contradiction to predictions based on field-free (e,2e) recollision dynamics, but, in overall agreement with recent semi-classical calculations for He.

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“…Multiple ionization is thus via electron interaction with the ionic core. Evidence for this mechanism includes large reductions in nonsequential ionization rates for circularly polarized fields and more recently from the momentum distribution of the recoil ions [16,17], and coincidence measurements between ions and ejected electrons [18]. However, it has proved difficult to predict quantitative yields for the product ions without using large-scale calculations through the S-matrix approach [19] or by obtaining a time-dependent solution of the Schrödinger equation [20].…”

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Suppression of Multiple Ionization of Atomic Ions in Intense Ultrafast Laser Pulses

Greenwood

Johnston²,

McKenna³

et al. 2002

Phys. Rev. Lett.

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The interaction of an intense laser field with a beam of atomic ions has been investigated experimentally for the first time. The ionization dynamics of Ar 1 ions and Ar neutrals in a 60 fs, 790 nm laser pulse have been compared and contrasted at intensities up to 10 16 W cm 22 . Our results show that nonsequential ionization from an Ar 1 target is strongly suppressed compared with that from the corresponding neutral target. We have also observed for the first time the strong field ionization of high lying target metastable levels in the Ar 1 beam. DOI: 10.1103/PhysRevLett.88.233001 PACS numbers: 32.80.Fb There is considerable current interest in the interaction of high intensity ͑10 13 10 18 W cm 22 ͒ radiation with dilute matter, where the external electric field strength becomes comparable to molecular bond and valance electron binding strengths. Studies have been carried out with targets of atoms, molecules, clusters [1], and most recently molecular ions [2,3], in order to elucidate the new physics observable in this highly nonlinear regime. These include the study of high harmonic generation [4], strong field effects in molecular dissociation, and the enhancement of multiple ionization in atoms [5,6]. Work is currently underway to generate attosecond pulses through harmonic generation [7,8], and coherent x-ray generation could be possible for highly charged ions in the presence of superintense fields [9,10].Both experiment and theory have shown that, in femtosecond laser pulses, multiple ionization of atoms is enhanced by nonsequential processes [5,6,11,12]. The physical model which best describes the observed behavior is known as the "atomic antenna" [13] or "recollision" [14,15] model. In this picture the first electron is removed from the atom by tunneling through the barrier created by interaction of the external field with the atomic potential. This electron is then accelerated in the external field and, depending on the initial phase, can return to the singly charged ion with energies up to 3.17U P [6], where U P is the classical ponderomotive energy in the field. Multiple ionization is thus via electron interaction with the ionic core. Evidence for this mechanism includes large reductions in nonsequential ionization rates for circularly polarized fields and more recently from the momentum distribution of the recoil ions [16,17], and coincidence measurements between ions and ejected electrons [18]. However, it has proved difficult to predict quantitative yields for the product ions without using large-scale calculations through the S-matrix approach [19] or by obtaining a time-dependent solution of the Schrödinger equation [20].By including the effects of excitation from the recollision followed by tunneling [21] and taking into account the Coulomb focusing on the active electron [22], better agreement with experiment has been obtained. The importance of multiple returns to the core has been demonstrated experimentally by a reduction in nonsequential ionization when few cycle pulses are used [23]....

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Electron Energy Spectra from Intense Laser Double Ionization of Helium

Cited by 104 publications

References 23 publications

Correlated electron emission in laser-induced nonsequence double ionization of helium

Correlated electron emission in laser-induced nonsequence double ionization of helium

Strongly directed electron emission in non-sequential double ionization of Ne by intense laser pulses

Suppression of Multiple Ionization of Atomic Ions in Intense Ultrafast Laser Pulses

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