Speckle correlation as a monitor of X-ray free electron laser induced crystal lattice deformation

TL;DR

This study demonstrates that speckle correlation analysis of X-FEL scattering patterns can effectively monitor irreversible lattice deformations in crystals caused by high-intensity X-ray pulses, revealing a threshold response.

Contribution

The paper introduces a speckle correlation method to track X-FEL induced lattice changes, providing new insights into beam-induced structural dynamics.

Findings

Irreversible lattice changes occur after high-fluence X-ray pulses.

A threshold response to X-FEL pulse intensity is identified.

Speckle correlation effectively monitors lattice rearrangements.

Abstract

X-ray free electron lasers (X-FELs) present new opportunities to study ultrafast lattice dynamics in complex materials. While the unprecedented source brilliance enables high fidelity measurement of structural dynamics, it also raises experimental challenges related to the understanding and control of beam-induced irreversible structural changes in samples that can ultimately impact the interpretation of experimental results. This is also important for designing reliable high performance X-ray optical components. In this work, we investigate X-FEL beam-induced lattice alterations by measuring the shot-to-shot evolution of near-Bragg coherent scattering from a single crystalline germanium sample. We show that X-ray photon correlation analysis of sequential speckle patterns measurements can be used to monitor the nature and extent of lattice rearrangements. Abrupt, irreversible changes are observed following intermittent high-fluence monochromatic X-ray pulses, thus revealing the existence of a threshold response to X-FEL pulse intensity.