Response time of electrons to light in strong-field ionization of polar molecules

TL;DR

This paper investigates how the permanent dipole and asymmetric Coulomb potential influence electron response times during strong-field ionization of polar molecules, using numerical and analytical models to explain observed photoelectron momentum distributions.

Contribution

The study introduces a strong-field model that accounts for both permanent dipole and asymmetric Coulomb effects, providing a quantitative explanation of electron response times in polar molecules.

Findings

Permanent dipole effects alter electron response times to light.

Asymmetric Coulomb potential influences sub-cycle ionization dynamics.

Model accurately reproduces observed offset angles in photoelectron distributions.

Abstract

We study tunneling ionization of HeH+ in strong elliptical laser fields numerically and analytically. The calculated photoelectron momentum distribution (PMD) show two different offset angles corresponding to ionization events occurring in the first and the second half cycles of one laser cycle. When the larger angle is greater than the angle of a model symmetric molecule with a similar ionization potential to the polar molecule, the smaller angle is smaller than the symmetric molecule. Using a developed strong-field model that consider effects of both the permanent dipole (PD) and the asymmetric Coulomb potential, we are able to quantitatively reproduce these phenomena. We show that the PD effect can increase (decrease) the response time of electrons within polar molecules to light in photoemission, thereby increasing (decreasing) the offset angle related to the first (second) half cycle of a laser cycle. The laser-dressed asymmetric Coulomb potential near the atomic nuclei also plays an important role in the sub-cycle-related response time and offset angle. This model may be useful for quantitatively studying attosecond ionization dynamics of polar molecules in strong laser fields.