Resonant control of photoelectron directionality by interfering one- and two-photon pathways

TL;DR

This paper demonstrates how interference between one- and two-photon ionization pathways can control the direction of photoelectrons in helium, with high efficiency near resonances, using multichannel quantum defect and R-matrix calculations.

Contribution

It introduces a novel coherent control scheme for photoelectron directionality in helium using multichannel quantum defect and R-matrix methods.

Findings

90% of photoelectrons near resonance flip emission direction.

Control is effective by tuning optical phase, electric field, and energy.

Large fraction of ionized electrons are unaffected, posing experimental challenges.

Abstract

Coherent control of interfering one- and two-photon processes has for decades been the subject of research to achieve the redirection of photocurrent. The present study develops two-pathway coherent control of ground state helium atom above-threshold photoionization for energies up to the $N=2$ threshold, based on a multichannel quantum defect and R-matrix calculation. Three parameters are controlled in our treatment: the optical interference phase $\Delta\Phi$, the reduced electric field strength $\chi=\mathcal{E}_{\omega}^2/{\mathcal{E}_{2\omega}}$, and the final state energy $\epsilon$. A small energy change near a resonance is shown to flip the emission direction of photoelectrons with high efficiency, through an example where $90\%$ of photoelectrons whose energy is near the $2p^2\ ^1S^e$ resonance flip their emission direction. However, the large fraction of photoelectrons ionized at the intermediate state energy, which are not influenced by the optical control, make this control scheme challenging to realize experimentally.