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Electron Matter-Wave Vortices in DoublePhotoionization of Helium by Attosecond PulsesTo cite this article: J. M. Ngoko Djiokap et al 2017 J. Phys.: Conf. Ser. 875 022014

 

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Electron Matter-Wave Vortices in Double Photoionization of Helium byAttosecond Pulses

J.M. Ngoko Djiokap∗ 1, A.V. Meremianin†, N.L. Manakov†, S.X. Hu‡, L.B. Madsen§,and Anthony F. Starace∗ 2

∗ Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588-0299, USA† Department of Physics, Voronezh State University, Voronezh 394006, Russia

‡ Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA§ Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark

Double photoionization of helium by a pairof time-delayed, elliptically-polarized attosecondpulses is shown to produce two-electron momen-tum distributions that exibit two-start spiral vortexstructures. These structures originate from Ram-sey interference of the created pair of two-electronwavepackets, each carrying a total angular momen-tum of unity. The predicted vortex-shaped patternsoccur for any energy partitioning between electrons,and are exquisitely sensitive to the time delay be-tween the two pulses, their relative phase, their ellip-ticity and handedness. Moreover, these kinds of vor-tices occur for both in-plane (cf. Figs. 1, 2) and out-of-plane detection geometries; however, they onlyoccur for fixed angular separation p̂1 · p̂2 between theelectron momenta.

We solve ab initio the seven-dimensional two-electron, time-dependent Schrödinger equation andanalyze the results using perturbation theory. Suchvortices are general phenomena, as similar patternshave been predicted for both atomic [1] and molecu-lar [2] single-electron ionization processes. Recently,similar Fermat spiral vortices were observed in anexperiment [3] involving femtosecond multiphotonionization of potassium. Those results are consistentwith our theoretical predictions for both photoioniza-tion [1] and multiphoton ionization [4] of helium.

Figure 1. In-plane detection geometry in which p1,p2

are ejected back-to-back (BTB) with unequal energysharing (UES). This plane is defined by the major (ϵ̂)and minor (ζ̂) axes of the polarization ellipse; it is or-thogonal to the laser propagation direction, k̂.

P-,x (a.u.)

P-,

y (a

.u.)

-1 0 1

-1

0

10 1 2 3 6

BTBUES

φ1=0φ2=0 T=275 asτ=275 as

ξ1=-ξ2=+0.8

Counter-rotating

Figure 2. Fermat spiral vortex pattern in double ioniza-tion of He by a pair of oppositely elliptically polarizedattosecond pulses (with degrees of circular polarizationξ1 =−ξ2 =+0.8) for the detection geometry in Fig. 1.The vortex pattern is exhibited by the P− distributionin the polarization plane, where P− = (p1 −p2)/2 de-fines the relative momentum of the ionized pair of elec-trons. The two pulses have the same carrier frequency of90 eV; intensity of 50 TW/cm2; carrier-envelope phaseϕ1 = ϕ2 = 0; and are delayed in time by τ = T , whereT = 275 as is the total duration of the six-cycle pulses.

Research supported in part by the U.S. Departmentof Energy, Office of Science, Basic Energy Sciences,Grant No. DE-FG02-96ER14646.

References

[1] J.M. Ngoko Djiokap et al. 2015 Phys. Rev. Lett.115 113004

[2] K.-J. Yuan et al. 2016 Phys. Rev. A 93 053425

[3] D. Pengel et al. 2017 Phys. Rev. Lett. 118 053003

[4] J.M. Ngoko Djiokap et al. 2016 Phys. Rev. A94 013408

1E-mail: marcelngoko@unl.edu2E-mail: astarace1@unl.edu

ICPEAC2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 875 (2017) 022014 doi:10.1088/1742-6596/875/3/022014

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