Ultrafast energy-dispersive soft-x-ray diffraction in the water window with a laser-driven source

TL;DR

This paper introduces a novel ultrafast, energy-dispersive soft-x-ray diffraction technique using a laser-driven high-harmonic source, enabling femtosecond resolution across the water window for studying rapid structural dynamics.

Contribution

It demonstrates a new method for energy-dispersive soft-x-ray diffraction with femtosecond resolution using broadband HHG sources, expanding capabilities for ultrafast material studies.

Findings

Successfully probed laser-induced structural dynamics in a Mo/Si superlattice.

Measured strain dynamics via Bragg peak shifts at ~500 eV.

Validated the approach with soft-x-ray scattering simulations.

Abstract

Time-resolved soft-x-ray-diffraction experiments give access to microscopic processes in a broad range of solid-state materials by probing ultrafast dynamics of ordering phenomena. While laboratory-based high-harmonic generation (HHG) light sources provide the required photon energies, their limited photon flux is distributed over a wide spectral range, rendering typical monochromatic diffraction schemes challenging. Here, we present a scheme for energy-dispersive soft-x-ray diffraction with femtosecond temporal resolution and photon energies across the water window from 200 to 600 eV. The experiment utilizes the broadband nature of the HHG emission to efficiently probe large slices in reciprocal space. As a proof-of-concept, we study the laser-induced structural dynamics of a Mo/Si superlattice in an ultrafast, non-resonant soft-x-ray diffraction experiment. We extract the underlying strain dynamics from the measured shift of its first order superlattice Bragg peak in reciprocal space at photon energies around 500 eV via soft-x-ray scattering simulations.