Single-photon ionization of H$_2^+$ in near-circular laser fields with lower photon energy

TL;DR

This paper investigates single-photon ionization of H$_2^+$ in near-circular laser fields, revealing an offset angle in the photoelectron momentum distribution influenced by molecular potential effects, with implications for ultrafast molecular probing.

Contribution

It provides a combined numerical and analytical study of the offset angle phenomenon in molecular ionization, highlighting the role of the molecular Coulomb potential and proposing its use for ultrafast molecular imaging.

Findings

Offset angle varies with internuclear distance and laser frequency.

Molecular Coulomb potential near atomic centers influences the PMD.

Phenomenon differs from atomic ionization and attoclock experiments.

Abstract

We study single-photon ionization of aligned H$_2^+$ in low-intensity near-circular laser fields with lower photon energy numerically and analytically. The photoelectron momentum distribution (PMD) within the laser polarization plane, obtained by numerical simulations, shows a remarkable offset angle, which changes with changing the internuclear distance and the laser frequency. This phenomenon is different from that observed in recent experiments [Science 370, 339 (2020)] which is related to the PMD along the propagation direction of the laser. This phenomenon holds even for H$_2^+$ with short-range Coulomb potentials but disappears for atoms, different from that observed in attoclock experiments. We show that the molecular Coulomb potential near the two atomic centers plays an important role here and theory models associated with more accurate continuum wave function of the molecule are needed for reproducing this phenomenon. This phenomenon can be useful for ultrafast probing of molecules with high resolution of several attoseconds or even zeptoseconds.