# High-energy-resolution off-resonant spectroscopy with self-seeded x-ray free-electron laser pulses

## TL;DR

This paper introduces a new method for high-energy-resolution x-ray spectroscopy using self-seeded free-electron lasers, enabling precise and efficient material analysis.

## Contribution

The paper presents the first implementation of HEROS using self-seeded XFEL pulses for improved x-ray absorption measurements.

## Key findings

- HEROS-based spectra showed consistent line shapes regardless of sample thickness.
- HEROS enables scan-free measurements with reduced core-hole lifetime broadening and self-absorption effects.
- The method is suitable for ultrafast dynamics studies in various materials and conditions.

## Abstract

This paper presents the implementation of high-energy-resolution off-resonant spectroscopy (HEROS) measurements using self-seeded x-ray free-electron laser (XFEL) pulses. This study systematically investigated XFEL conditions, including photon energy and accumulated shot numbers, to optimize the measurement efficiency for copper foil samples near the K-edge. The x-ray absorption spectra reconstructed using HEROS were compared with those derived from fluorescence-yield measurements. The HEROS-based spectra exhibited consistent line shapes independent of the sample thickness. The potential application of HEROS to high-temperature copper was also explored. HEROS offers distinct advantages including scan-free measurement of x-ray absorption spectra with reduced core-hole lifetime broadening and self-absorption effects. Using self-seeded XFEL pulses, HEROS facilitates single-shot-based pump–probe measurements to investigate the ultrafast dynamics in various materials and diverse conditions.