Femtosecond X-ray absorption spectroscopy in warm dense matter

TL;DR

This paper demonstrates that betatron radiation from laser-plasma interactions enables femtosecond X-ray absorption spectroscopy, allowing real-time investigation of ultrafast atomic and electronic processes in warm dense matter.

Contribution

It introduces a novel femtosecond X-ray source based on betatron radiation suitable for routine ultrafast spectroscopy experiments.

Findings

Measured electron temperature rise below 100 fs

Showed potential for studying non-equilibrium dynamics

Validated betatron radiation for femtosecond XAS

Abstract

Exploring and understanding ultrafast processes at the atomic level is a scientific challenge. Femtosecond X-ray Absorption Spectroscopy (XAS) is an essential experimental probing technic, as it can simultaneously reveal both electronic and atomic structures, and thus unravel their non-equilibrium dynamic interplay which is at the origin of most of the ultrafast mechanisms. However, despite considerable efforts, there is still no femtosecond X-ray source suitable for routine experiments. Here we show that betatron radiation from relativistic laser-plasma interaction combines ideal features for femtosecond XAS. It has been used to investigate the non-equilibrium transition of a copper sample brought at extreme conditions of temperature and pressure by a femtosecond laser pulse. We measured a rise time of the electron temperature below 100 fs. This first experiment demonstrates the great potential of the betatron source and paves the way to a new class of ultrafast experiments.