Strong-Field Polarizability-Enhanced Dissociative Ionization

TL;DR

This paper explores how intense femtosecond laser pulses cause dissociative ionization of HeH+ molecules, revealing a mechanism where molecules align and stretch before ionization, with implications for isotope effects.

Contribution

The study introduces a semi-classical model showing the role of polarizability and molecular alignment in laser-induced dissociation, aligning with experimental data.

Findings

Molecules align along laser polarization before ionization

Ionization rate increases with internuclear distance and alignment

Qualitative agreement with experimental observations

Abstract

We investigate dissociative single and double ionization of HeH+ induced by intense femtosecond laser pulses. By employing a semi-classical model with nuclear trajectories moving on field-dressed surfaces and ionization events treated as stochastical jumps, we identify a strong-field mechanism wherein the molecules dynamically align along the laser polarization axis and stretch towards a critical internuclear distance before getting dissociative ionized. As the tunnel-ionization rate is greater for larger internuclear distance and for aligned samples, ionization is enhanced. The strong dynamical rotation is traced back to a maximum in the parallel component of the internuclear-distance-dependent polarizability tensor. Qualitative agreement with our experimental observations is found. Finally the criteria for observing the isotope effect for the ion angular distribution is discussed.