Field-Induced Tunneling Ionization and Terahertz-Driven Electron Dynamics in Liquid Water

TL;DR

This study reveals how intense terahertz pulses induce tunnel ionization in liquid water, enabling control over electron dynamics and dielectric properties through external electric fields.

Contribution

It demonstrates the role of terahertz-driven fields in inducing irreversible ionization and controlling charge behavior in liquid water, a novel approach to manipulating aqueous systems.

Findings

Terahertz pulses induce tunnel ionization in water molecules.

Localized electrons significantly alter water's optical properties.

External fields enable steering of charge dynamics in water.

Abstract

Liquid water at ambient temperature displays ultrafast molecular motions and concomitant fluctuations of very strong electric fields originating from the dipolar H2O molecules. We show that such random intermolecular fields induce tunnel ionization of water molecules, which becomes irreversible if an external terahertz (THz) pulse imposes an additional directed electric field on the liquid. Time-resolved nonlinear THz spectroscopy maps charge separation, transport and localization of the released electrons on a few-picosecond time scale. The highly polarizable localized electrons modify the THz absorption spectrum and refractive index of water, a manifestation of a highly nonlinear response. Our results demonstrate how the interplay of local electric field fluctuations and external electric fields allows for steering charge dynamics and dielectric properties in aqueous systems.