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.

Figure 1

(a) Distribution of correlated electron momenta along the laser polarization for Helium DI irradiated by 800 nm, $4.5\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ laser pulses. The black box indicates the $2\sqrt{U_p}$ boundary of electron momentum. The model calculations under various circumstances yield very different momentum distribution patterns (see text for details): (b) the laser field is removed and the tunneled electrons are replaced by a beam of projectile electrons; (c) the electron-electron Coulombic interaction is replaced with a Yukawa potential; (d) the nuclear Coulomb potential is softened.

Figure 2

(a), (b) Two trajectory configurations responsible for the fingerlike structure. DI yield versus laser phase at recollision (c) and at DI moment (d). Here, the statistics is only collected for the DI trajectories that contribute to the prominent fingerlike structure, i.e., the regimes of $1.5\mathrm{a}.\mathrm{u}.<|k_i^{\parallel }|<2.0\mathrm{a}.\mathrm{u}.$ and $2.5\mathrm{a}.\mathrm{u}.<|k_j^{\parallel }|<3.0\mathrm{a}.\mathrm{u}.$, where $i$, $j=1$, 2, $i\ne j$. The dashed curves represent laser fields.

Figure 3

Correlated parallel momentum distributions with additional conditions on the relative perpendicular momentum between two electrons, i.e., for (a) $0\le k_{12}^{\perp }\le 0.2$, (b) $0.4\le k_{12}^{\perp }\le 0.6$, (c) $1.2\le k_{12}^{\perp }\le 1.4$. (d) The overall relative perpendicular momentum distribution.