Real-time observation of frustrated ultrafast recovery from ionisation in nanostructured SiO2 using laser driven accelerators

TL;DR

This study uses transient photoabsorption to observe ultrafast electron dynamics in nanostructured SiO2, revealing a sharp increase in electron lifetime linked to nanostructure effects and phonon interactions, advancing understanding of radiation damage processes.

Contribution

It introduces a novel methodology combining laser-driven accelerators and optical streaking to directly observe ultrafast electron recovery in nanostructured SiO2, highlighting the role of phonon-assisted quenching.

Findings

Electron lifetime increases sharply from <1 ps to >50 ps near the phonon-fracton crossover.

Nanostructure influences the recovery process, extending electron energy states.

Results suggest a link between nanostructure, phonon interactions, and radiation damage dynamics.

Abstract

Ionising radiation interactions in matter can trigger a cascade of processes that underpin long-lived damage in the medium. To date, however, a lack of suitable methodologies has precluded our ability to understand the role that material nanostructure plays in this cascade. Here, we use transient photoabsorption to track the lifetime of free electrons (t_c) in bulk and nanostructured SiO2 (aerogel) irradiated by picosecond-scale (10^-12 s) bursts of X-rays and protons from a laser-driven accelerator. Optical streaking reveals a sharp increase in t_c from < 1 ps to > 50 ps over a narrow average density (p_av) range spanning the expected phonon-fracton crossover in aerogels. Numerical modelling suggests that this discontinuity can be understood by a quenching of rapid, phonon-assisted recovery in irradiated nanostructured SiO_2. This is shown to lead to an extended period of enhanced energy density in the excited electron population. Overall, these results open a direct route to tracking how low-level processes in complex systems can underpin macroscopically observed phenomena and, importantly, the conditions that permit them to emerge.