Laser-driven nanoplasmas in doped helium droplets: Local ignition and anisotropic expansion

TL;DR

This study demonstrates that doping helium droplets with a small xenon cluster induces rapid ionization and anisotropic expansion under laser irradiation, revealing a novel two-step ionization mechanism and nanoplasma formation.

Contribution

It uncovers a new two-step ionization process in doped helium droplets and highlights the role of nanoplasma shape and resonant absorption in laser interactions.

Findings

Doping helium droplets with xenon triggers complete ionization at sub-threshold laser intensities.

A two-step ionization mechanism involving avalanche ionization and resonant absorption was identified.

The resulting nanoplasma exhibits anisotropic expansion influenced by its cigar-shaped geometry.

Abstract

Doping a helium nanodroplet with a tiny xenon cluster of a few atoms only, sparks complete ionization of the droplet at laser intensities below the ionization threshold of helium atoms. As a result, the intrinsically inert and transparent droplet turns into a fast and strong absorber of infrared light. Microscopic calculations reveal a two-step mechanism to be responsible for the dramatic change: Avalanche-like ionization of the helium atoms on a femtosecond time scale, driven by field ionization due to the quickly charged xenon core is followed by resonant absorption enabled by an unusual cigar-shaped nanoplasma within the droplet.