## Research Papers in Physics and Astronomy

#### ORCID IDs

J. M. Ngoko Djiokap https://orcid.org/0000-0003-4702-3544

#### Date of this Version

2021

#### Citation

PHYSICAL REVIEW A 103, 053110 (2021)

DOI: 10.1103/PhysRevA.103.053110

#### Abstract

We use time-delayed, counter-rotating, circularly polarized few-cycle attosecond nonoverlapping pulses to study the temporal coherent control of the resonant process of two-photon double ionization (TPDI) of hydrogen molecule via doubly excited states for pulse propagation direction along ˆk either parallel or perpendicular to the molecular axis ˆR. For ˆk ‖ ˆR and a pulse carrier frequency of 36 eV resonantly populating the Q_{2} 1∏ ^{+} _{u} (1) doubly excited state as well as other 1∏ ^{+} _{u} doubly excited states, we find that the indirect ionization pathway through these doubly excited states changes the character of the kinematical vortex-shaped momentum distribution produced by the two direct ionization pathways from fourfold to twofold rotational symmetry. This result is similar to what found in TPDI of the He atom involving 1Po± 1 doubly excited states [Ngoko Djiokap and Starace, J. Opt. 19, 124003 (2017)]; however, angular distributions exhibiting a quantum beat effect between the ground state and a doubly excited state seen for the He atom are observed here for its molecular counterpart with an anomaly in shape and magnitude, not in frequency. The sixfold differential probability integrated over the azimuthal angle of the photoelectron pair shows that this anomaly is due to autoionization decays and quantum beats between doubly excited states. For ˆk ⊥ ˆR and a broadband pulse carrier frequency of 30 eV populating the Q_{1} 1∏ ^{+} _{u} (1), Q_{1} 1∑ ^{+} _{u} (1), Q_{2} 1∏ ^{+} _{u} (1), and Q_{1} 1∑ ^{+} _{u} (2) doubly excited states, the momentum distribution is shown to exhibit dynamical electron vortices with four spiral arms, which originates from the interplay between the ^{1}Δ ^{+} _{g} , ^{1}Π^{+} _{g} , and ^{1}Σ ^{+} _{g} dynamical ionization amplitudes. Our treatment within either the adiabatic-nuclei approximation or fixed-nuclei approximation shows that the latter provides a very good account for this correlated process.

#### Included in

Atomic, Molecular and Optical Physics Commons, Elementary Particles and Fields and String Theory Commons, Plasma and Beam Physics Commons

## Comments

©2021 American Physical Society