Angular distribution in two-photon double ionization of helium by intense attosecond soft-x-ray pulses

Abstract

We investigate two-photon double ionization of helium by intense (≈ 10 15 W/cm 2 ) ultrashort (≈ 300 as) soft X-ray pulses (E = 91.6 eV). The time-dependent two-electron Schrödinger equation is solved using a coupled channel method. We show that for ultrashort pulses the angular distribution of ejected electrons depends on the pulse duration and provides novel insights into the role of electron correlations in the two-electron photoemission process. The angular distribution at energies near the "independent electron" peaks is close to dipolar while it acquires in the "valley" of correlated emission a significant quadrupolar component within a few hundred attoseconds.

Ultrafast Probing of Collective Electron Dynamics Driven by Dielectronic Repulsion

“…As a consequence, ultrafast electron-electron interactions inside atoms have so far been investigated only to a limited extent. Most investigations have primarily focused on the influence of dielectronic interactions on two-photon double ionization of He [4,[6][7][8][9][10]. In addition, electron-electron interactions have also been used to measure the distance between two electrons in He, by tracking the motion of a single excited electron [4].…”

Electron correlation in two-photon double ionization of helium from attosecond to XFEL pulses

“…With the advent of intense XUV pulses, the focus has shifted from single-photon double ionization [13][14][15][16][17] and intense-IR laser ionization by rescattering ( [18][19][20] and references therein) to multiphoton ionization. Two-photon double ionization (TPDI) has recently received considerable attention, both in the so-called "nonsequential" or "direct" regime (39.5 eV < ω < 54.4 eV), where the electrons necessarily have to share energy via electron-electron interaction to achieve double ionization [21][22][23][24][25][26][27][28][29][30][31][32][33][34], and in the "sequential" regime ( ω > 54.4 eV), where electron-electron interaction is not a priori necessary [11,[35][36][37][38][39][40].…”

Polarization control of direct (non-sequential) two-photon double ionization of He

“…At present, although the available intensities of VUV light sources are still in the perturbative regime (up to 10 15 W cm −2 ), these intensities allow probes of processes involving more than one photon [2]. Thus, many theoretical works have focused on two-photon double ionization (TPDI) of helium (see, e.g., [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]): 2γ + He → He 2+ + e − + e − . ('d') This direct ('d'), or non-sequential, two-electron process occurs simultaneously with sequential ('s') processes.…”