High-resolution inelastic x-ray scattering at the high energy density scientific instrument at the European X-Ray Free-Electron Laser.

L Wollenweber ,Gianluca Geloni ,G Monaco ,R Redmer ,Zuzana Konôpková ,S Göde ,S H Glenzer ,A Jenei ,Valerio Cerantola ,I Uschmann ,Dirk O Gericke ,David Mcgonegle ,C Strohm ,Th Tschentscher ,Adrien Descamps ,Thomas G White ,G Gregori ,Ian Thorpe ,J B Hastings ,J H Eggert ,Benjamin K Ofori-Okai ,O Karnbach ,Thomas R Preston ,Berit Marx-Glowna ,Christian Plückthun ,L B Fletcher ,A J Comley ,R Loetzsch ,Oliver Humphries ,Karen Appel ,C A J Palmer ,J S Wark ,E E Mcbride ,U Zastrau

doi:10.1063/5.0022886

Abstract

We introduce a setup to measure high-resolution inelastic x-ray scattering at the High Energy Density scientific instrument at the European X-Ray Free-Electron Laser (XFEL). The setup uses the Si (533) reflection in a channel-cut monochromator and three spherical diced analyzer crystals in near-backscattering geometry to reach a high spectral resolution. An energy resolution of 44 meV is demonstrated for the experimental setup, close to the theoretically achievable minimum resolution. The analyzer crystals and detector are mounted on a curved-rail system, allowing quick and reliable changes in scattering angle without breaking vacuum. The entire setup is designed for operation at 10 Hz, the same repetition rate as the high-power lasers available at the instrument and the fundamental repetition rate of the European XFEL. Among other measurements, it is envisioned that this setup will allow studies of the dynamics of highly transient laser generated states of matter.

Highlights

Inelastic X-ray Scattering (IXS) is a powerful tool to measure material dynamics by comparing the energy and momentum of a photon before and after the interaction process
The accessible processes can be categorized by the value of the energy transfer and range from keV individual electron responses in Compton scattering processes1–3 through collective electronic excitations such as plasmons and x-ray Raman scattering in the eV range4–6 down to structural dynamics on the order of meV.7–10
We have successfully demonstrated a new capability of the High Energy Density (HED) instrument to resolve inelastic x-ray scattering with a spectral resolution of 44 meV

Summary

INTRODUCTION

Inelastic X-ray Scattering (IXS) is a powerful tool to measure material dynamics by comparing the energy and momentum of a photon before and after the interaction process. This technique at high resolution can resolve small energy and momentum transfers and enables direct temperature measurements of temperatures below 1 eV either through Doppler broadening or by measurements of Stokes/anti-Stokes lines in detailed balance.30 By comparing these to the intensity of the elastic scattering, it is possible to determine diffusive modes in amorphous materials and plasmas.. They have a lower relative blurring compared to the analyzer center, as indicated by the dotted lines (right axis) This enables, for a certain range of momentum transfers, two ways of measurements. The two outer analyzers have a higher minimum scattering vector than the central analyzer Their relative k-blurring is smaller than that of the central analyzer at the cost of a lower intensity of the scattered radiation on the analyzers due to the angular dependence of the scattering cross section for horizontally polarized x rays, shown by the dotted lines (Fig. 4). The complete setup is kept at a typical vacuum level of 10−4 mbar to enable compatibility with high-intensity and high-power laser experiments

DISPERSION AND ENERGY RESOLUTION

PULSE LENGTH CONSIDERATIONS

Findings

CONCLUSION