Polarization in strong-field ionization of excited helium

Abstract

We analyze how bound-state excitation, electron exchange and the residual binding potential influence above-threshold ionization (ATI) in helium prepared in an excited p state, oriented parallel and perpendicular to a linearly polarized mid-IR field. Using the ab initio B-spline algebraic diagrammatic construction (ADC), and several one-electron methods with effective potentials, including the Schrödinger solver Qprop, modified versions of the strong-field approximation and the Coulomb quantum-orbit strong-field approximation (CQSFA), we find that these specific physical mechanisms leave significant imprints in ATI spectra and photoelectron momentum distributions. Examples are changes of up to two orders of magnitude in the high-energy photoelectron region, and ramp-like structures that can be traced back to Coulomb-distorted trajectories. The present work also shows that electron exchange renders rescattering less effective, causing suppressions in the ATI plateau. Due to the long-range potential, the electron continuum dynamics are no longer confined to the polarization axis, in contrast to the predictions of traditional approaches. Thus, one may in principle probe excited-state configurations perpendicular to the driving-field polarization without the need for orthogonally polarized fields.1

Exploring symmetries in photoelectron holography with two-color linearly polarized fields

“…It is not yet clear how it will affect targets with specific geometries and/or internal degrees of freedom, which, per se, cause phase changes and modulations in holographic structures [72,96,[147][148][149]. Furthermore, the Coulomb potential may lead to a strong deviation from the widely used the mapping p 0 = −A(t ) in orthogonally polarized fields [47], or may move rescattering away from the polarization axis [111]. The present work is intended as a step towards the understanding of symmetry in a Coulomb-distorted context, an in providing a theoretical framework for a generic (r, s) two-color linearly polarized field.…”

“…encodes the geometry of the initial electronic orbital, which, in the present publication, we take to be 1s. For other types of orbitals in the CQSFA we refer to [97,[111][112][113].…”

“…Due to the presence of the Coulomb potential, the above discussion only holds approximately. The interplay between the driving field and the Coulomb potential is highly non-trivial, and even small changes in the electron's binding energy can lead to qualitatively different behaviors for the CQSFA (for a recent example see [111]).…”

“…With that purpose in mind, we will use the Coulomb Quantum-Orbit Strong-Field Approximation (CQSFA) [105]. The CQSFA is a path-integral strong-field approach that accounts for the driving field and the residual binding potential on equal footing, and has been applied by us to photoelectron holography by monochromatic fields [106][107][108][109][110][111]. Apart from excellent agreement with experiments [97,112,113], the CQSFA allows unprecedented control about what type of interference leads to specific structures, as specific types of orbits may be switched on and off at will.…”

Exploring symmetries in photoelectron holography with two-color linearly polarized fields

“…With that purpose in mind, we will use the Coulomb Quantum-Orbit Strong-Field Approximation (CQSFA) [111]. The CQSFA is a path-integral strong-field approach that accounts for the driving field and the residual binding potential on equal footing, and has been applied by us to photoelectron holography by monochromatic fields [112][113][114][115][116][117]. Apart from excellent agreement with experiments [101,118,119], the CQSFA allows unprecedented control about what type of interference leads to specific structures, as specific types of orbits may be switched on and off at will.…”