Probing warm dense matter using femtosecond X-ray absorption spectroscopy with a laser-produced betatron source

Abstract

Exploring and understanding ultrafast processes at the atomic level is a scientific challenge. Femtosecond X-ray absorption spectroscopy (XAS) arises as an essential experimental probing method, as it can simultaneously reveal both electronic and atomic structures, and thus potentially unravel their nonequilibrium 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 nonequilibrium dynamics 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 experiment demonstrates the great potential of the table-top betatron source which makes possible the investigation of unexplored ultrafast processes in manifold fields of research.

Hard X Rays from Laser-Wakefield Accelerators in Density Tailored Plasmas

“…Betatron x-ray sources [1,2] from laser-plasma interaction have the potential to become invaluable tools to reveal ultrafast dynamics at the atomic scale length. In particular, their broadband spectrum and femtosecond duration are ideal features for femtosecond (fs) xray absorption spectroscopy applications [3]. However, they remain marginal in the panel of the commonly used x-ray sources, mainly because of their limited photon energies and relatively low average flux.…”

Attosecond betatron radiation pulse train

“…We close with two example applications where the suggested technique has the potential to drive forward development. Betatron radiation has already been used in laboratory astrophysics, when warm dense matter (WDM) samples were investigated employing XAS 48 . It takes advantage of the broadband photon spectrum in the keV region, where most elements' absorption edges are located.…”

The versatile X-ray beamline of the Munich Compact Light Source: design, instrumentation and applications

“…Recently, data acquisition times as short as 1 min have been successfully demonstrated at a quality comparable with synchrotrons (Huang et al, 2020). Other laboratory XAS setups, based on X-ray tubes (Seidler et al, 2014;Né meth et al, 2016;Bè s et al, 2018;Błachucki et al, 2019;Jahrman et al, 2019), laser-plasma sources (Uhlig et al, 2013), laser-betatron ones (Mahieu et al, 2018) or high harmonic generation (Pertot et al, 2017;Popmintchev et al, 2018) typically operate at a lower X-ray energy below 10 keV and typically require exposure times of tens of minutes to hours. This elongated acquisition time originates from the lower brilliance of X-ray tubes compared with ICSs, like at the MuCLS.…”