Attosecond coherence control of Helium ions ensemble

J.V. Hern 'andez, Brett D. Esry

Steve Gilbertson, Michael Chini, Sabih D. Khan +3 more

J. M. Ngoko Djiokap, Alexei V. Meremianin, Nikolai L. Manakov +3 more

Saad Mehmood, Eva Lindroth, Luca Argenti

The authors show how an attosecond XUV-pump IR-probe sequence can be used to ionize the helium atom and create a polarized ion whose coherence is controllable through the pump-probe delay and can be reconstructed from the picosecond fluctuations of the ionic dipole caused by fine-structure interactions.

Saad Mehmood, Eva Lindroth, Luca Argenti

The ionization of atoms with sequences of attosecond pulses gives rise to excited ionic states that are entangled with the emitted photoelectron. Still, the ionic ensemble preserves some coherence that can be controlled through the laser parameters. In helium, control of the $2s/2p\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}$ coherence is mediated by the autoionizing states below the $N=2$ threshold [Phys. Rev. Res. 3, 023233 (2021)]. In the present work we study the role of the resonances both below and above the $N=3$ threshold on the coherence of the $N=3\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}$ ion, in the attosecond pump-probe ionization of the helium atom, which we simulate using the newstock ab initio code. Due to the fine-structure splitting of the $N=3{\mathrm{He}}^{+}$ level, the ionic dipole beats on a picosecond timescale. We show how, from the dipole beating, it is possible to reconstruct the polarization of the ion at its inception.

Saad Mehmood, Coleman Cariker, Tor Kjellsson Lindblom +2 more